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Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

ENGINEERING CONSTRUCTION STANDARD

ECS 06-0023

SECONDARY DISTRIBUTION NETWORK EARTHING
CONSTRUCTION

Network(s): EPN, LPN, SPN

Summary: This standard provides guidance for field staff on the application of earthing to the
secondary distribution HV and LV underground cable and overhead line networks.

Owner: Stephen Tucker Date: 28/07/2014

Approved By: Steve Mockford Approved Date: 04/08/2014

This document forms part of the Company’s Integrated Business System and its requirements are mandatory throughout UK
Power Networks. Departure from these requirements may only be taken with the written approval of the Director of Asset
Management. If you have any queries about this document please contact the author or owner of the current issue.

Circulation External
UK Power Networks G81 Website
Contractors
All UK Power Networks ICPs/IDNOs
Asset Management
Capital Programme Meter Operators
Connections
HSS&TT
Network Operations
UK Power Networks Services
Other

© UK Power Networks 2014 All rights reserved Page 1

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

THIS IS AN UNCONTROLLED DOCUMENT, THE READER MUST CONFIRM ITS VALIDITY BEFORE USE

© UK Power Networks 2014 All rights reserved Page 2

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

Revision Record

Version 4.0 Review Date 28/07/2019

Date 28/07/2014 Author Stephen Tucker

Revised to align and ensure consistency with EDS 06-0014, EDS 07-0102, the Overhead Line
manual and other earthing standards. Feedback from Network Operations also incorporated.
The main changes include:

• Earth bar introduced (Section 6.3.2).

• New EDS 07-0102 designs incorporated, including integral and basement substation design with
embedded mesh (Section 6.4.4).

• Lower rebar connection removed from all earthing arrangements (Section 6.4).

• Earth grate introduced as option for emergency asset replacement (Section 6.4.7).

• Preformed operator earth mat introduced for pole-mounted equipment (Section 7.2.5).

• Use of aluminium earth conductor and copper/aluminium transition shown on pole-mounted
earthing arrangement drawings (Section 7.3).

• PME earth electrodes clarified (Section 8.2.1).
• Simple rod and conductor electrode options added (Section 10).

• Materials (Section 12) and connections (Section 13) updated.
• Standard earth resistance measurement methods added (Section 15).

Version 3.0 Review Date 20/09/2017

Date 20/09/2012 Author Stephen Tucker

All sections revised. Pole, LV and NetMap sections added. Document reviewed for publishing on
G81 website

Version 2.1 Review Date 20/02/2014

Date 28/09/2011 Author Stephen Tucker

Version 2.0 Review Date 20/10/2013

Date 20/10/2010 Author Mariann Mulligan

Document rebranded

Version 1.0 Review Date 20/02/2012
Date 20/02/2009 Author Stephen Tucker
Original

© UK Power Networks 2014 All rights reserved Page 3

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

Contents

1 Introduction ................................................................................................................................................... 5
2 Scope.............................................................................................................................................................. 6
3 Abbreviations ................................................................................................................................................ 6
4 Definitions...................................................................................................................................................... 6
5 Theft of Earthing ............................................................................................................................................ 7

5.1 Use of Aluminium ......................................................................................................................................... 7
5.2 Sites where Theft has Occurred.............................................................................................................. 7
6 Secondary Distribution Substations............................................................................................................... 8
6.1 New Substations ........................................................................................................................................... 8
6.2 Substation Refurbishment and Asset Replacement/Enhancement ............................................................. 8
6.3 Installation Requirements ............................................................................................................................ 9
6.4 Typical Earthing Arrangements................................................................................................................... 17
7 Overhead Lines ......................................................................................................................................... 26
7.1 Design Overview ......................................................................................................................................... 26
7.2 Installation Requirements .......................................................................................................................... 26
7.3 Earthing Arrangements............................................................................................................................... 29
8 LV Earthing................................................................................................................................................... 39
8.1 Design Overview ......................................................................................................................................... 39
8.2 Installation Requirements .......................................................................................................................... 39
9 Customer Installations ................................................................................................................................. 43
9.1 Earth Terminal ............................................................................................................................................ 43
9.2 Connection to Supply Neutral Conductor at the Cut-out ........................................................................... 43
9.3 Connection to Cable Sheath/Armouring at the Cut-out ............................................................................. 43
9.4 Earth Fault Loop Impedance....................................................................................................................... 43
10 Earth Electrode Options............................................................................................................................... 44
11 NetMap Earthing Information System......................................................................................................... 45
12 Materials ...................................................................................................................................................... 46
13 Connection Techniques................................................................................................................................ 47
14 Warning Labels ............................................................................................................................................ 50
15 Measurements............................................................................................................................................. 51
15.1 Overview................................................................................................................................................... 51
15.2 Test Equipment......................................................................................................................................... 51
15.3 Earth Resistance Measurement using the Fall-of-Potential Method ....................................................... 51
15.4 Earth Resistance Measurement using the Comparison Method .............................................................. 53
15.5 Earth Resistance Measurement using a Clamp Meter ............................................................................. 53
16 References ....................................................................................................................................................... 54
Appendix A – Purpose of Earthing........................................................................................................................ 55
Appendix B – LV Earthing Systems ....................................................................................................................... 56

© UK Power Networks 2014 All rights reserved Page 4

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

1 Introduction

This standard provides guidance for field staff on the application of earthing for:

New secondary substations (Section 6.1).
• Asset replacement or a material alteration at secondary substations (Section 6.2).

Fencing and door replacement at secondary substations (Section 6.3.5).
Pole-mounted equipment and overhead networks (Section 7).
LV networks (Section 8).
Customer installations (Section 9).

This standard also includes information on earth electrode options (Section 10), NetMap
earthing maps (Section 11), materials (Section 12), connection techniques (Section 13),
warning notices (Section 14) and measurements (Section 15).

This standard is not a substitute for the design standards which cover the earthing design in
detail. In general the earthing design should be provided by the project designer/planning
engineer and this standard can then be used to install the design.

• The earth resistance for all new secondary substations shall be specified by the
designer/planning engineer – the generic ‘1 ohm’ rule is no longer applicable.

• The earthing system at all new secondary substations shall, as a minimum, consist of a
ring electrode around the site (except basement or integral sites where this is not
practicable), a minimum of two earth rods, connections to the rebar and bonding
between all equipment and main earth terminal, unless a site specific design has been
provided by a competent earthing specialist.

• When carrying out asset replacement, fence/door replacement or other works at a
secondary substation the earthing shall be reviewed and enhanced if required to
ensure that it complies with the latest standards.

• The ring electrode around a secondary substation shall use bare copper conductor,
buried directly in the soil; insulated or covered conductor that has previously been used
at some installations shall not be used.

• The minimum size of bonding conductor shall be 35mm2 aluminium or 16mm2 copper.

• Aluminium shall be used for all earthing and bonding above ground where practicable
and where it is vulnerable to theft. Bare aluminium shall not be used below ground.

• The use of aluminium tape around the inside walls of the substation as previously used
in London is not required unless it is specified as part of the earthing design (e.g.
embedded mesh integral and basement substation designs).

• A dedicated earth bar shall be used for marshalling all earth connections.

• Connection of lower rebar in a standard 3m x 3m plinth is no longer required.

• An LV earth terminal shall only be provided if it is appropriate and safe to do so and
should be specified within the design along with the type of earthing system to be used.

This standard supersedes all legacy documentation on earthing associated with the
HV and LV networks.

© UK Power Networks 2014 All rights reserved Page 5

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

2 Scope

This standard applies to the construction of earthing for secondary distribution substations,
11/6.6kV overhead networks and LV networks.

3 Abbreviations

Term Definition

CNE Combined Neutral Earth cable (refer to Section 0)
Ellipse UK Power Networks Asset Register
EPR Earth Potential Rise (refer to Section 0)
NetMap UK Power Networks GIS system
PME Protection Multiple Earthing (refer to Section 0)
ROEP Rise of Earth Potential (refer to Section 0)
SNE Separate Neutral Earth cable (refer to Section 0)

4 Definitions

This section defines some of the terms used in this guide. Further definitions can be found in
EDS 06-0012.

Cable - Combined Neutral Earth (CNE)
A CNE cable has a combined neutral and earth metallic outer sheath with a PVC covering
and is typically used in a PME (protective multiple earthing) LV earthing system.

Cable - Separate Neutral Earth (SNE)
An SNE cable has separate neutral and earth conductors. Generally the neutral conductor is
a fourth core and the earth conductor forms a protective sheath.

COLD Site
A COLD site is a grid, primary or secondary substation where the earth potential rise (EPR)
is less than 430V. Note: Higher limits may apply at grid or supergrid substations with fast
acting protection.

HOT Site
A HOT site is a grid, primary or secondary substation where the earth potential rise (EPR) is
greater than 430V.

Earth Potential Rise (EPR) or Rise of Earth Potential (ROEP)
EPR is the potential (or voltage) rise that occurs on any metalwork due to the current that
flows through the ground when an earth fault occurs on the HV or LV network. Note: Some
current will flow through the cable sheath back to the source and some will flow through the
ground, it is only the current that flows through the ground that causes the earth potential
rise.

Installing a buried grading electrode around the site and equipment and bonding exposed
metalwork together helps to reduce potential differences between a person's hands and
feet such that any current flowing through the body is kept to a safe level.

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Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
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Step, Touch and Transfer Potentials
The step potential is the potential difference between a person’s feet assumed to be 1m
apart. The touch potential is the potential difference between a person’s hands and feet
when standing up to 1m away from any earthed metalwork they are touching. The transfer
potential is the potential transferred by means of a conductor between an area with a
significant rise of earth potential and an area with little or no rise of earth potential, and
results in a potential difference between the conductor and earth in both locations.

Substation Earthing Database

The substation earthing database contains the classification (HOT or COLD) of all grid and
primary substations together with the details of the EPR and other relevant earthing
information. Refer to EDS 06-0002 for further details.

Protective Multiple Earthing (PME)

PME is the most common form of earthing provided at new installations. A single conductor
for neutral and earthing functions is utilised and an earth terminal is provided at the
customer’s installation. The customer’s earthing may be connected to this terminal providing
the relevant requirements in BS 7671 are satisfied. In some cases it is not appropriate to
provide a PME earth terminal, either due to the nature of the distribution system or due to
the type of installation itself.

5 Theft of Earthing

5.1 Use of Aluminium

The theft of copper earthing continues to be a significant national problem. Therefore the
earthing system shall be constructed to ensure that it is secure and not vulnerable to theft.
Aluminium shall be used wherever practicable for all new or replacement earthing above
ground at all secondary substations and pole-mounted sites.

Note:
• Aluminium shall not be used for earthing conductors that are in direct contact or buried

within the ground.
• Small sections of copper/aluminium shall be avoided as multiple joints in close proximity

may be problematic.
• In some cases it may be prudent to replace existing copper with aluminium.
• Where the use of aluminium is impractical or not suitable (e.g. connections to rebar) then

copper may be used as a last resort provided it is suitably protected from theft, e.g.
installed in tubing filled with resin, buried in concrete or pinned etc.

5.2 Sites where Theft has Occurred

When entering a site where earth connections have been stolen, safety precautions are
necessary to reduce the risk of shock – refer to EOS 09-0067 for further information.

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Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
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Date: 28/07/2014

6 Secondary Distribution Substations

6.1 New Substations

The earthing design for all new ground-mounted secondary (20kV, 11kV, 6.6kV, 3kV and
2kV) substations shall be carried out by the designer/planning engineer to ensure that the
design criteria detailed in EDS 06-0014 are fulfilled. The designer/planning engineer shall
provide the following for each project:

• An earthing design/construction form specifying the required HV earth resistance,
whether the HV and LV earths should be combined or separated and the COLD/HOT
status of the site.
An earthing drawing either based on one of the standard UK Power Networks’
arrangements in Section 6.4 or a bespoke arrangement.

Note: It is no longer acceptable to use the generic ‘1 ohm’ rule. In many situations a
substation may be acceptable with a resistance value greater than 1Ω. However, in some
situations (in particular when supplied from a solidly earthed grid/primary substation, or if
an overhead line section makes up part of the circuit), a value less than 1Ω may be
required to achieve an acceptable site.

Using the available information the installer shall:

1. Install the earthing as detailed on the provided drawing. Note: Although any additional
electrode should be specified in the earthing design it is acceptable for the installer to
use different combinations of earth rod, conductor and mats provided that the required
earth resistance is achieved and the installation satisfies the requirements detailed in this
document.

2. Apply the earthing requirements shown in Section 6.3 to the earthing arrangement.
3. Select the appropriate materials, connections and warning labels from Sections 12, 13

and 14.
4. Measure the value of the HV and LV (if required) earth resistance in accordance with

Section 15 to confirm that the required value has been achieved.
5. Commission the earthing system in accordance with ECP 11-0503.

Any queries or changes to the earthing design shall be referred back to the
designer/planning engineer.

6.2 Substation Refurbishment and Asset Replacement/Enhancement

When work is carried out at existing substations, e.g. civil refurbishment, asset replacement
or enhancement, the earthing shall be reviewed, and brought in line with current
requirements; however the earthing enhancement should be proportional to the actual work
being carried out and be practical to install.

The earthing should, where possible, be based around the standard arrangements detailed
in Section 6.4; Section 6.4.7 includes some specific examples of earthing enhancement
during asset replacement.

Metallic fences, gates and doors require particular attention to ensure they are correctly
bonded in accordance with Section 6.3.5.

© UK Power Networks 2014 All rights reserved Page 8

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3 Installation Requirements

6.3.1 General

The sections below detail the common earthing requirements that shall be applied to all
secondary substations, unless a site specific design has been provided by an earthing
specialist.

If the site is designed with separate HV and LV earths, care is required to ensure that all
earthed metalwork is more than 2m from any other metalwork and that separate HV/LV
earths are not inadvertently combined.

6.3.2 Earth Bar

All earth connections shall be labelled and connected via separate connections to a
dedicated earth bar (GRP/brick-built designs) or marshalling bar (integral/basement designs)
which in turn shall be connected to the main transformer/switchgear earth terminal to allow:

• Operational personnel to determine if the earthing is intact when entering the substation.
• The earthing to be easily identified.
• The earth resistance to be measured using a clamp meter.

Note: At new enclosed substations the HV earth bar within the LV cabinet/pillar shall not be
used to marshal the earthing connections as access, particularly at IDNO substations, to the
LV cabinet/pillar is not always available. However it is acceptable to use the HV earth bar
within the LV cabinet/pillar at existing outdoor sites for all earth connections to prevent theft.

Refer to Sections 6.3.11 and 6.3.14 for combined and separated HV/LV earth configurations.

Earth Bar Marshalling Bar

© UK Power Networks 2014 All rights reserved Page 9

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3.3 HV Earth Electrodes

Bare copper cable or tape and copper clad rods (refer to Section 12) shall be used as earth
electrodes. Section 10 provides electrode options to obtain various resistance values. The
minimum sizes of earth electrode are shown below.

Function Source Bare Stranded Hard Drawn Bare Copper Tape
HV Earth Electrode Fault Level Copper Conductor

Earth Rod Electrode Up to 8kA 70mm2 25mm x 3mm
Up to 12kA 120mm2 or 2 x 70mm2 25mm x 4mm
Up to 15kA 2 x 70mm2 25mm x 6mm
Any
1m or 1.2m Copper Clad Rods (16mm or 19mm diameter)

Note:
• Earth electrode should be installed underneath the HV cable (or LV cable) at a depth of

at least 600mm to provide physical protection and surrounded by 150mm of fine texture
non-corrosive soil which has been firmly consolidated. If the indigenous soil is hostile to
copper (i.e. known to be overly acidic or alkaline) suitable surrounding soil should be
imported.
• In areas of high soil resistivity additional earth electrodes may be specified in the design
consisting of either horizontal conductor, long vertical earth rods or a mixture of both.
Where difficult installation problems are envisaged or found (such as boulder clay
beneath the ground) vertical earth rods may need to be installed in pre-drilled holes and
backfilled with appropriate earthing compound (refer to Section 12), rather than driven in
by mechanical means.
• When laying stranded conductor, care should be taken to avoid distorting and opening
the individual strands as this increases the probability of corrosion.

6.3.4 Equipment Bonding

All current carrying items of equipment including the HV switchgear, LV pillar/cabinet/board
and LV ACB shall be bonded to the main earth terminal using an independent connection.
The minimum sizes of the bonding conductor (refer to Section 12) are shown below.

Function Source Covered Stranded Cable Tape
Any Fault Level
70mm2 Copper 25mm x 3mm Copper
Above Ground Up to 8kA 120mm2 or 2 x 70mm2 Copper 25mm x 4mm Copper
Bonding Up to 12kA 2 x 70mm2 Copper 25mm x 6mm Copper
Up to 15kA 120mm2 Aluminium 25mm x 6mm Aluminium
Up to 8kA 2 x 120mm2 Aluminium 40mm x 6mm Aluminium

Up to 15kA

All other non-current carrying items of equipment (e.g. control units, RTUs, battery chargers
etc.) shall be bonded to the main earth terminal using a minimum of 35mm2 covered
stranded aluminium cable, 16mm2 covered stranded copper cable or equivalent.

© UK Power Networks 2014 All rights reserved Page 10

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3.5 Metallic Fences and Gates

The diagrams below show typical earthing arrangements for metallic fences within 2m of
accessible earthed equipment and more than 2m away from the equipment or other earthed
metalwork.

Metallic Fence within 2m of Equipment

Duplicate connections An earth grading electrode should be:
to the HV earth or main •Installed outside the fence at a distance of 300-
earth terminal
500mm away or, if not practical, directly
underneath/just inside the fence (as shown)
•70mm2 bare stranded copper conductor or
25mm2 x 4mm bare copper tape earth
•Installed at a depth of 500mm (300mm
minimum) below ground level
•Connected to each fence post

Gate §B3u5rimedmc2oanlunmecintioiunmboertw1e6emnmg2acteopppoesrtsc:overed
stranded cable

§F3le5xmibmle2 connection between gate and gate posts:
aluminium or 16mm2 copper covered

stranded cable or 16mm2 tinned copper braid

Metallic Fence more than 2m away from Equipment or Equipment in GRP/Brick Enclosure

To eliminate stray voltages a single driven earth
rod shall be installed:
§ At each corner fence post
§ At each gate post and connected to the

fence/gate

Gate Buried connection between gate posts:
§ 35mm2 aluminium or 16mm2 copper covered

stranded cable

Flexible connection between gate and gate posts:
§ 35mm2 aluminium or 16mm2 copper covered

stranded cable or 16mm2 tinned copper braid

Note: Where the substation fence is bonded to the HV earth, no other metallic fencing or
conducting material shall be abutted to the fence or within 2 metres of it. Otherwise any
voltage rise at the substation may be transferred to a remote location far from the substation
where it will be impossible to protect against dangerous touch voltages. Insulating fence
panels or stand-off insulators can be used to achieve this requirement. Metallic third party
fences should not be within simultaneous touching distance (2m) of metalwork/fences
connected to the HV earth. If necessary a ‘floating’ (isolated) section of fence or non-
conductive barrier should be introduced outside the substation boundary (refer to

© UK Power Networks 2014 All rights reserved Page 11

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

ECS 06-0022 for further information on the use of insulated panels and insulated stand-offs).
If this is not practicable then specialist advice should be sought.

Care should be exercised when replacing wooden fencing with a metallic type (e.g.
Pallisade, Expamet, 358 etc) since its bonding requirements are more onerous, and it is
unlikely that a fence earthing system will exist. It is not sufficient simply to replace wooden
panelling with metallic, nor is it sufficient to merely bond metallic fence panels together
above ground without a buried electrode system.

Metallic fences even if painted or powder coated shall be considered as bare metal unless
covered in an approved insulated coating that will not degrade over time.

6.3.6 Metallic Doors

Generally, due to the small size of most secondary substations, metallic doors should be
bonded to the HV earth as shown below unless a site specific design is provided.

Note: The ‘grading electrode’ outside the substation doors may be omitted if specified in the
design and only if there is concrete or tarmac outside the substation and the substation is
designed with combined HV/LV earthing and is a COLD site.

Unless specified otherwise an earth 1m To HV
grading electrode shall be: Metallic Earth
Doors
• Installed outside the door at a Connection between door and door
distance of 1m in front of the door 500mm frame: 35mm2 aluminium or 16mm2
and 500mm beyond each door frame
copper covered stranded cable or
• 70mm2 bare stranded copper conductor 16mm2 tinned copper braid
or 25mm2 x 4mm bare copper tape earth
To HV Connection between door
• Installed at a depth of 300- Earth frame and HV earth: minimum
500mm below ground level 35mm2 aluminium or 16mm2
copper covered stranded cable
• Covered with a 100mm thickness of
concrete to protect against damage
or theft

• Connected to the HV earth at each end

However if metallic doors are installed more than 2m away from other earthed metalwork
and are not connected to the HV earth an independent earth electrode shall be installed and
connected to each door (refer to EDS 06-0014 for further details).

6.3.7 Ancillary Metalwork

All other exposed and normally un-energised metalwork inside the substation perimeter
boundary (e.g. ventilation ducts, staircases, louvres etc) within 2m of other earthed
metalwork shall be bonded to the HV earth using 35mm2 covered stranded aluminium cable
or 16mm2 covered stranded copper cable to avoid any potential differences between
different items of metalwork.

Note: Metal frames and other metallic parts that form part of a GRP enclosure do not need
to be bonded to the HV earth.

© UK Power Networks 2014 All rights reserved Page 12

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3.8 Ducting and Ventilation Shafts

Metallic ducts and ventilation shafts passing through indoor secondary substations provide
an electrical path between the inside and outside of the substation. If they are bonded to the
HV earth, they could transfer potential outside the substation zone and may pose a risk to
the general public. Generally it is impractical to install measures to control touch and step
potentials where these vents emerge. Therefore one of the following approaches, in order of
preference1, shall be taken to minimise risk to the public:

• Bond the ducts and ventilation shafts to the HV earth (unless the EPR is greater than
430V), and install them such that they are out of reach (i.e. 3m above ground or other
foothold) where they emerge from the substation..

• Leave the ducts and ventilation shafts un-bonded, and install them such that there is no
possibility of a simultaneous touch contact between the ducts and other earthed
metalwork. This may require the installation of insulated ducts or barriers. A warning
label can be installed as a further precaution.

6.3.9 HV Cables

All cable earth screens shall be bonded to the main earth terminal in accordance with
Section 4 of the 11kV Cable Jointing manual.

6.3.10 LV Cables

• CNE cables - the outer sheath of the cable shall be connected to the neutral bar in the
LV pillar/cabinet in accordance with Section 4 of the LV Cable Jointing manual.

• SNE cables - the outer sheath and armouring shall be bonded together and connected
to the neutral bar in the LV pillar/cabinet/board. The neutral conductor shall be connected
to the neutral bar in the LV pillar/cabinet/board in accordance with Section 4 of the LV
Cable Jointing manual.

1 The risk to the public can be reduced by leaving the ducts and ventilation shafts un-bonded. However this may

introduce a touch potential risk to staff inside the substation since the ducts and vents may act as a remote earth
and will therefore be at a different potential to HV earth during fault conditions; the risk of an HV fault happening
occurring while staff are on site and bridging a gap between the HV earth and the duct is thought to be extremely
small and is outweighed by the risk to public which may occur if the systems are bonded.,

© UK Power Networks 2014 All rights reserved Page 13

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3.11 Combined HV/LV Earths

If the EPR is less than 430V (COLD site) an LV earth is not required. The LV neutral-earth
link in the LV cabinet, pillar or board, that bonds the LV neutral to the substation HV earth,
shall be in place so that the HV and LV earths are combined.

Note: Where an LV ACB is mounted directly on to the transformer and an LV cabinet or
board is not present the transformer earth terminal shall be bonded to the neutral using the
appropriate bonding conductor from Section 6.3.4 as shown below.

HV Switchgear Transfomer LV Distribution Board Earth bonding
L1 or electrode

L2
L3

E
N

LV Cables

HV Cables HV/LV Neutral-
HV Electrode Resistance (as specified) Earth Link in
Place

Main Earth
Terminal

Transformer Earth Bar Located in Cable Pit or
Earth Stud Marshalling Bar Mounted on Wall

LV Cabinet

Neutral Earth Equipment
Bar Bar and Ancillary
Metalwork
Removable Link
Bonding

LV Board Additional HV Duplicate Connections Connection to
Earth Electrode to HV Earth Mat Reinforcement
Neutral/
Earth Bar Rebar/Mesh

Neutral – Earth link

LV Cabinet ACB

© UK Power Networks 2014 All rights reserved Page 14

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.3.12 Separate HV/LV Earth Additional Requirements

In addition to the requirements detailed in Section 6.3, the requirements detailed in this
section shall be applied at sites with separate HV and LV earths.

Note: If a supply is provided to a HOT site (e.g. grid or primary substation) or a National
Grid substation refer to EDS 08-0121 for additional earthing requirements.

6.3.13 LV Earth

The LV earth electrode shall be:

Selected from Section 10 to provide a resistance of 20Ω or less.
• Separated from any HV electrode by at least 8m.
• Installed under an LV cable in the cable trench wherever practicable to enhance its

security.
• Connected to the LV neutral bar in the LV pillar/cabinet using 70mm2 covered copper

conductor (also laid under an LV main cable) in accordance with the LV Cable Jointing
manual.

6.3.14 Neutral-Earth Link

The HV/LV neutral-earth link shall be removed for a separated HV/LV earth as shown
below.

HV Switchgear Transfomer LV Distribution Board Earth bonding or
electrode
L1
L2 PVC covered conductor
L3 within 8m of bare HV
electrode or metallic
sheathed HV cables

E
N

HV Cables HV/LV Neutral- LV Cables
HV Electrode Resistance (as specified)
Earth Link LV Electrode Resistance
Removed (not to exceed 20Ω)

Main Earth
Terminal

8m minimum

© UK Power Networks 2014 All rights reserved Page 15

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

Transformer Earth Bar Located in Cable Pit or
Earth Stud Marshalling Bar Mounted on Wall

LV Cabinet

Neutral HV Earth Equipment
Bar Bar and Ancillary
Metalwork
Link Removed HV Earth in LV
Cabinet/Board Bonding

Separate Additional HV Duplicate Connections Connection to
LV Earth Reinforcement
Earth Electrode to HV Earth Mat Rebar/Mesh

Neutral bar Neutral – Earth link
LV earth to be connected here

As Delivered Removed

6.3.15 Warning Notices for Separate HV/LV Earths

Where the HV and LV earths are separated, warning labels (EDS 07-0009.118 and EDS 07-
0009.117) as detailed in Section 14 shall be installed as required.

6.3.16 Lighting and Socket Supplies

Care shall also be taken with lighting and socket supplies to avoid operator contact between
different earthing systems. Therefore at sites with separate HV and LV earths:

• Light switches and conduits shall preferably be plastic; metallic light switches and
conduits shall not be installed within 2m of any metalwork bonded to the HV earth.

• All 13A sockets shall be disconnected or removed (for disconnection of sockets in LV
cabinets refer to Schneider instruction EM-MS-06-005-r3 and EM-MS-06-009-r0).

• RTU supplies shall be provided via a 500VA isolation transformer with a 5kV insulation
rating (refer to Schneider instruction2).

6.3.17 Street Lighting Columns and Street Furniture

New substations with separate HV and LV earths shall not be installed within 2m of street
lighting columns or other street furniture

2 The Schneider LV cabinet design is due to be modified in 2014 to enable the isolation transformer to be fitted
on-site as required.

© UK Power Networks 2014 All rights reserved Page 16

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4 Typical Earthing Arrangements

The general principles for the construction of a substation earthing system are as follows:

Bare copper clad earth electrodes using the minimum sizes specified in 6.3.3.
• A ring of bare earth electrode buried around the perimeter of the substation (or

alternatively buried around the inside of the substation) at a depth of 500-600mm (except
at integral and basement substations where this is not achievable).
• A minimum of two earth rods installed on two corners of the substation (or alternatively
internally) and connected to the ring.
• Two connections from the ring onto a dedicated earth bar or main earth terminal.
• An earth electrode passing underneath any HV switchgear or LV operating position and
connected to the other electrode or an insulated or earthed operator platform.
• Connections to the reinforcement rebar or mesh.
• Additional electrode and rods, as necessary, to enable the required earth resistance to
be achieved.
• All items of HV equipment and exposed metalwork bonded to the main earth
bar/terminal.

The section contains typical earthing arrangements based on the above principles, showing
the installation of the HV and LV (if required) earthing, for the following types of installation:

• New GRP, brick-built, compact, micro pad-mount and outdoor substations.
• Integral, basement and raft substations.
• Customer HV supplies and substations.
• Existing outdoor substations.

The standard substation design drawings contained in EDS 07-0102 (and listed below) also
include an associated earthing arrangement (on sheet 2).

Description Drawing No

GRP Unit/Package Substation with Standard Plinth EDS 07-0102.01

GRP Unit/Package Substation with Fully-bunded Plinth EDS 07-0102.02

GRP Elevated Substation with Fully-bunded Plinth EDS 07-0102.21

GRP Micro Substation with Standard Plinth EDS 07-0102.03

GRP Compact Substation with Standard Plinth EDS 07-0102.04

GRP Metering Substation with Standard Plinth EDS 07-0102.16

Freestanding Brick-built Unit/Package Substation (3.6m x 3.6m) EDS 07-0102.18

Freestanding Brick-built Substation for a Single Transformer without/with EDS 07-0102.05-06
ACB and LV Board (4m x 5m)

Integral Substation for a Single Transformer without/with ACB and LV Board EDS 07-0102.07-08

Basement Substation EDS 07-0102.09

Micro Substation EDS 07-0102.10

Compact Substation EDS 07-0102.11

Fenced Outdoor Substation with Micro and Ring Main Unit EDS 07-0102.12

Fenced Outdoor Substation with Micro and Extensible Switchgear EDS 07-0102.13

© UK Power Networks 2014 All rights reserved Page 17

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.1 GRP and Brick-Built Substations (Combined HV/LV Earths)

The general earthing arrangement for GRP or brick-built substations with a combined HV/LV
earth (COLD site) is shown below (refer to EDS 07-0102 for specific designs).

11

Combined HV/LV Earths
Neutral/Earth Link In

Transformer To LV Cable To HV
Neutral Earth
Main Earth Bar/Terminal
5 4

4 LV
3 6 RMU

Additional HV Earth 22
Electrode/Rods
Note: Not all equipment
(as required to achieve bonding is shown
earth resistance)

LV CNE Cable

HV Earth Electrode Bare Copper Conductor Bare Copper Tape
70mm2 25mm x 3mm
Primary Fault Level 120mm2 (or 2 x 70mm2) 25mm x 4mm
Up to 8kA 2 x 70mm2 25mm x 6mm
Up to 12kA
Up to 15kA

1 - 2.4m earth rods at rear corners
2 - Alternative internal 2.4m earth rods in place of external ones for brick-built substations 3
- HV electrode around the outer edge of foundation buried at a depth of 500-600mm
4 - HV electrode connecting each side of outer loop to main earth terminal 5
- Connection to reinforcement rebar/mesh
6 - Neutral/Earth link in place

© UK Power Networks 2014 All rights reserved Page 18

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.2 GRP and Brick-Built Substations (Separate HV/LV Earths)

The general earthing arrangement for GRP or brick-built substations with a separate HV/LV
earth (HOT site) is shown below (refer to EDS 07-0102 for specific designs).

11

Separate HV/LV Earths
Neutral/Earth Link Out

Transformer 7

Main Earth Bar/Terminal To LV Cable
Neutral
LV 5 To HV
RMU To LV Earth
Earth
6 4
7
4
3

2 2

Additional HV Earth Note: Not all equipment
Electrode/Rods bonding is shown

(as required to achieve
earth resistance)

LV Earth Connection (Insulated) HV/LV Separation
LV CNE Cable (8m minimum)

LV Earth Electrode/Rods
(max resistance 20Ω)

HV Earth Electrode Bare Copper Conductor Bare Copper Tape LV Earth
70mm 2 25mm x 3mm
Primary Fault Level 120mm2 (or 2 x 70mm2) LV earth connection – 70mm 2 PVC
Up to 8kA 25mm x 4mm covered stranded copper conductor
Up to 12kA 2 x 70mm 2 25mm x 6mm
Up to 15kA LV earth electrode – 70mm 2 bare
stranded copper conductor

1 - 2.4m earth rods at rear corners
2 - Alternative internal 2.4m earth rods in place of external ones for brick-built substations
3 - HV electrode around the outer edge of foundation buried at a depth of 500-600mm
4 - HV electrode connecting each side of outer loop to main earth terminal
5 - Connection to reinforcement rebar/mesh
6 - Neutral/Earth link removed
7 - Warning labels

© UK Power Networks 2014 All rights reserved Page 19

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.3 Compact (including Micro and Pad-mount) Substations

The earthing arrangement for a compact/micro substation without an enclosure is shown
below. These are generally supplied via the overhead line network and therefore the HV and
LV earths are generally separated as shown and detailed in Section 6.3.12. However if the
EPR is less than 430V, the HV and LV earths may be combined. Refer to EDS 07-0102 for
specific designs.

Note: If the compact is installed in a GRP enclosure the standard arrangements for a GRP
shown in 6.4.1 and 6.4.2 shall be used.

1 1
Separate HV/LV Earths
Separated Neutral/Earth Link Out
HV/LV Earths

7

9 LV HV

6 Neutral Earth
9

3 To HV Earth
7 Electrode

To LV Earth
Electrode
4
To LV Cable

55 Neutral and Sheath

HV/LV Separation

Additional HV Earth 2 2 (8m minimum) LV Earth Electrode/Rods

Electrode/Rods LV Earth Connection (max resistance 20Ω)
(as specified )

LV CNE Cable

1 1

Combined Combined HV/LV Earths
HV/LV Earths Neutral/Earth Link In

8

6 LV HV
Neutral Earth
8
3
4
55 To HV Earth
Electrode

Additional HV Earth 2 2
Electrode/Rods
(as specified )

HV Earth Electrode LV Earth
LV earth connection – 70mm 2 PVC
Primary Fault Level Bare Copper Conductor Bare Copper Tape covered stranded copper conductor

Up to 8kA 70mm 2 25mm x 3mm LV earth electrode – 70mm 2 bare
Up to 12kA stranded copper conductor
120mm2 (or 2 x 70mm2) 25mm x 4mm

Up to 15kA 2 x 70mm 2 25mm x 6mm

1 - 2.4m earth rods at rear corners 500mm behind plinth

2 - 2.4m earth rods at front corners 500mm in front of the plinth
3 - HV electrode in a ring around the substation, extending 500mm on all sides, buried at a depth of 500mm and
connected to the earth rods
4 - HV electrode connecting each side of outer loop to the main earth terminal
5 - HV electrode in two places between the earthing ring and the earth terminal, passing directly underneath
the positions where an operator is required to stand to open the front cover and carry out operations
6 - Connection to reinforcement rebar/mesh

7 - Neutral/Earth link removed 8 - Neutral/Earth link in place 9 - Warning labels

© UK Power Networks 2014 All rights reserved Page 20

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.4 Integral, Basement and Raft Substations

The standard arrangements shown in Section 6.4.1 and 6.4.2 should be used wherever
possible. However where the substation is situated within a building or on a raft, it is usually
impracticable to install one of these arrangements. Instead a standard approach should be
applied using earth rods installed through the substation floor or in the basement, external
electrodes underneath the HV cable, vertical piles and an embedded mesh within the floor
screed (to control the touch and step potentials). Some examples are shown below.

It is very important to consider the earthing prior to construction if a satisfactory earthing
system is to be designed. Refer to EDS 07-0102 for specific designs and EDS 06-0014 for
further information.

1b 1a Substation
2 2
(b) Earth Rod Installation through
Transformer 6 Substation Floor into Soil
Substation
Main Earth Terminal 3 Basement
4
5 (c) Earth Rod Installation through
LV RMU Basement into Soil

2 (d) Embedded Mesh within
Floor Screed
1c

2
1b 1a

(a) Overall Earthing Arrangement

1a - Main earth rods (length to be determined by calculation based
on target resistance value and soil resistivity)
1b - Optional additional earth rods to help achieve overall low resistance
1c - Optional bare earth electrode laid with incoming HV cables to
help achieve overall low resistance
2 - Connections to mesh embedded within concrete floor screed - two
per each sheet of mesh
3 - Main earth bar
4 - Wall-mounted earth ring above floor level/below door tread to
aid connections
5 - Main equipment bond (not all equipment shown)
6 - Doorframe and door bonding

© UK Power Networks 2014 All rights reserved Page 21

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.5 Customer HV Supplies and Substations

Some typical arrangements for customer substations with combined and separate HV/LV
earths are shown below. Refer to Section 7 in EDS 06-0017 for further information including
the interconnection of UK Power Networks and customer earthing systems.

Note: UK Power Networks is not responsible for the LV earth and the decision to combine or
separate the HV and LV earths is the customer’s responsibility. Care is required if LV
supplies (from the customer) are to be introduced into the UK Power Networks substation
and is generally only permissible for combined earthing systems.

Combined HV/LV Earths

UK Power Networks Customer 1
Substation Substation
8
1

Note: 3 5 Additional
3 electrode/rods
Equipment
bonding not (if required )

shown 7 LV
MU
RMU HV TX

6

Additional 4 5 43
3 2
electrode/rods 1
(if required ) 2 Customer LV SNE Cables

1

UK Power Networks Customer
Substation Substation

1 1

Note: 3 3
Equipment RMU MU
bonding not HV TX LV
6
shown

Additional 4 43 1
3 2 Customer LV SNE Cables
electrode/rods
(if required ) 2

1

1 - 2.4 m earth rods at 2 corners of substation (alternatively they can be installed internally) 2 -
HV electrode around the outer edge of foundation buried at a depth of 500-600mm
3 - HV electrode connecting outer loop to switchgear/transformer earth
terminal 4 - Connection to reinforcement rebar/mesh
5 - Interconnection via a link between UK Power Networks and Customer
substations 6 - Neutral-earth link in place
7 - HV cable screen insulated from earth
8 - Warning labels

© UK Power Networks 2014 All rights reserved Page 22

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

Separated HV/LV Earths

UK Power Networks Customer 1
Substation Substation
8
1

Note: 3 5 3
5
Equipment 7 LV
MU
bonding not 6
shown

RMU HV TX

Additional 4 43
electrode/rods 3
(if required )
1
1 2 2
HV/LV
Separation
(8m minimum)

LV Earth Cable (Insulated)

Customer LV SNE Cables

UK Power Networks Customer
Substation Substation

1 1

Note: 33
Equipment
bonding not RMU MU HV TX LV
6
shown 4
3
Additional 43 1
electrode/rods 2 2
(if required ) HV/LV
Separation
1 (8m minimum)

LV Earth Cable (Insulated)

Customer LV SNE Cables

1 - 2.4 m earth rods at 2 corners of substation (alternatively they can be installed internally)
2 - HV electrode around the outer edge of foundation buried at a depth of 500-600mm
3 - HV electrode connecting outer loop to switchgear/transformer earth terminal
4 - Connection to reinforcement rebar/mesh
5 - Interconnection via a link between UK Power Networks and Customer substations
6 - Neutral-earth link removed
7 - HV cable screen insulated from earth
8 - Warning labels

© UK Power Networks 2014 All rights reserved Page 23

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

6.4.6 Outdoor Substations

Outdoor secondary substations are no longer constructed except in Areas of Outstanding
Natural Beauty when a close boarded fence substation is required. Refer to EDS 07-
0102.12-13 for specific designs.

6.4.7 Asset Replacement

Earthing needs to be considered during asset replacement work at existing sites. The
installation of a complete earthing system based on a standard arrangement is rarely
practical. However the opportunity to enhance the earthing should be taken and the earthing
installed should seek to achieve as much of the following as possible, using the excavations
that are necessary for the remedial work:

• Buried bare electrode around the equipment at a depth of around 600mm and connected
to the main earth bar. Note: It is especially important to ensure that there is bare
electrode under the operator’s standing position – especially if metallic sheathed cables
are replaced with plastic cables (even short lengths) during a switchgear change.

• An embedded and bonded mesh or grate under the operator’s standing position if buried
electrode is not practical.

• One or two substantial earth rods connected to the buried earth electrode or the main
earth bar.

• Bonding of all equipment to the main earth bar.
• If a metallic fence and/or gates are present the requirements of Section 6.3.5 shall also

be applied.

Some typical examples for outdoor substations are shown below. If only the LV pillar is
being replaced the installation of a buried electrode system is unlikely to be practical but the
pillar shall be bonded to the main earth bar. The more equipment alterations and associated
excavations that are taking place, the more the earthing can be improved until a stage is
reached where it is close to one of the standard arrangements in the previous sections.

For basement and integral substations the standard approach outlined in Section 6.4.4 may
be used and is more likely to provide a more practical solution.

For emergency asset replacement or where the installation of buried electrode is not
practical a steel grate plate3 should be installed in front of the switchgear where the operator
would stand and connected to the main earth terminal using duplicate connections. The
grate should be securely embedded in the shingle or bolted to the concrete floor.

Some typical examples are shown overleaf.

3 The steel grate option is being trialled at the time of writing; contact the document author for further details.

© UK Power Networks 2014 All rights reserved Page 24

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

11

1 Transformer 2
Transformer RMU

3HVSwitch 3
gear
12 PillarLV

(b) Switchgear and Transformer Replacement

(a) Switchgear Replacement Only 1 - 1.2 m earth rods connected to
the buried electrode
11
2 - Buried bare copper earth electrode
Transformer 2 ring around and the switchgear and
LV RMU any other equipment

3 - Buried bare copper earth
electrode in front of the switchgear
where an operator stands when using
the switchgear

4 - Connection to equipment
earth terminal

3 HV Earth Electrode

Fault Level Bare Copper Bare Copper
Conductor Tape

(c) Switchgear, Transformer and LV Replacement Up to 8kA 70mm2 25mm x 3mm
Up to 12kA 2 x 70mm2 25mm x 4mm
Up to 15kA 2 x 70mm2 25mm x 6mm

Transformer
LV RMU

Steel Grate under
Operator Position

(d) Use of Steel Grate

© UK Power Networks 2014 All rights reserved Page 25

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7 Overhead Lines

This section provides an overview of the main overhead line and pole-mounted equipment
earthing requirements; refer to EDS 06-0015 for more detailed information. All overhead
earthing shall be constructed in accordance with the Overhead Line manual.

Note: It is particularly important during asset replacement or pole refurbishment that the
earthing is brought up to the latest standards and separated HV and LV earths are not
accidentally combined.

7.1 Design Overview

The following design criteria are used for all new and refurbished pole earthing:

• Transformers, switchgear with control units, switchgear with operating handles at low
level, cable terminations and surge arresters shall always be earthed.

• Poles with only cross-arms and hook-stick operated equipment may be left unearthed.
However where any item of equipment on the pole is connected to earth all steelwork on
the pole (including cross arms, pilot insulator pins, trussing gear, high voltage cable
boxes etc) shall be connected to the main earth.

• The maximum HV earth resistance value shall be 10Ω.
• The maximum LV earth resistance value shall be 20Ω.

7.2 Installation Requirements

7.2.1 General

The following general requirements apply to all pole earthing:

• All above ground earth conductors shall be insulated for a minimum of 3m above ground
level and mechanically protected (in accordance with the Overhead Line manual) for a
minimum of 2m above ground level.

• The HV earth electrode shall be installed at the base of the pole except at locations
where it is necessary for an operator to carry out switching operations. At these locations
the HV earth electrode shall be installed on the opposite side of the pole to the operating
position and 5m away from the operating position. Any earth conductor within 5m of the
operating position shall be insulated.

• The HV earth electrode system shall be installed at a minimum depth of 1m.
• The main earth conductor/electrode shall be insulated for a minimum of 1m below

ground level.
• Bare HV and LV earth electrodes buried in the ground shall be separated by a minimum

of 8m.
• HV and LV earthing systems on the same pole shall be segregated by a minimum of

120°and the insulation integrity maintained throug hout.
• HV and LV earth conductors buried in the ground shall be separated by a minimum

distance of 100mm.
• Earthing conductors associated with surge protection shall be kept as straight as

possible with no sharp bends.
• An earth mat shall be installed for all switchgear operated from ground level.

Note: Any deviation from these arrangements, or failure to maintain the local earthing
systems, can result in operators being placed at unacceptable risk.

© UK Power Networks 2014 All rights reserved Page 26

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.2.2 Location

The electrode system shall preferably be installed alongside hedges or in the pavement area
and the following locations shall be avoided:

• Where persons could stand whilst operating any pole-top equipment.
• Near metal fences, fence posts, buried cables, pipes.
• Near camping or caravan parks where persons may be bare foot.
• Across main farm gates.
• Near drinking troughs or areas where livestock regularly congregate.
• Across open fields where there is a risk of damage by ploughing or drainage works.

7.2.3 Earth Electrodes

The minimum earth electrodes are detailed below.

Function Network Fault Level Electrode
Earth Electrode
EPN Up to 4kA 35mm² Bare Hard Drawn Stranded Copper Cable
Rod Electrode SPN Up to 8kA 70mm² Bare Hard Drawn Stranded Copper Cable
EPN/SPN All 1m or 1.2m Copper Clad Earth Rods

7.2.4 Earthing and Bonding Conductors
The minimum size of earthing and bonding conductors are detailed below.

Function Network Fault Level Earthing and Bonding Conductors
Up to 4kA
Earth Conductor EPN 50mm2 Covered Stranded Aluminium Cable
35mm2 Covered Stranded Copper Cable
SPN Up to 8kA 120mm2 Covered Stranded Aluminium Cable
70mm2 Covered Stranded Copper Cable
Bonding EPN/SPN All 35mm2 Covered Stranded Aluminium Cable
Conductor
35mm2 Covered Stranded Copper Cable

7.2.5 Earth Mat 1000mm

A preformed earth mat (preferred and shown) or an earth mat 1000mm
constructed of bare conductor shall be:

• Approximately 1m x 1m in size.
• Installed directly below where the operator will stand when

operating the switchgear.
• Installed at a depth of 300mm below ground.
• Connected to the switch handle or control unit.
• Segregated from all other earthing conductors where possible.
• Protected above ground by a cable guard.
• Embedded below ground in earthing compound (two bags below

and above) to protect against theft (preformed mat only). Further
details will be included in the revised Overhead Line manual.

© UK Power Networks 2014 All rights reserved Page 27

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
7.2.6 Surge Arresters Date: 28/07/2014
Where surge arresters are installed:

• The main earth conductor between the surge arrester and the electrode system shall be
as short and straight as possible with no sharp bends.

• Except at locations where it is necessary for an operator to carry out switching
operations, the electrode shall be installed at the base of the pole.

• At locations where it is necessary for an operator to carry out switching operations the
earth electrode shall be installed 5m away from the pole to avoid unacceptable step
potentials close to the operator. Any earth conductor within 5m of the operating position
shall be insulated. The insulated conductor shall be installed inside a PVC duct to
provide additional mechanical protection and insulation. It also serves to maintain the
conductor in a slow bend which improves lightning performance.

• The main earth conductor shall be insulated to a depth of 1m below ground level.
• The earth electrode resistance value shall not exceed 10Ω.

7.2.7 HV Steelwork

All HV pole-top steelwork supporting live equipment e.g. cross-arms, equipment supports
etc., shall be bonded together using the bonding conductor detailed in 7.2.4. The bonded
steelwork shall only be earthed if it is necessary to earth other equipment on the pole.

7.2.8 H-Poles

Where H-poles are fitted with cross-bracing equipment, the lowest cross-brace shall be not
less than 3m above the ground; where a cross-brace is found to be less than 3m above
ground it shall be repositioned. On an earthed pole the cross-brace shall be bonded to the
pole-top steelwork and on an unearthed pole it shall remain unbonded and unearthed.

All cable supports accessible from ground shall be bonded together and to a separate earth
on the opposite side to the main HV earth.

7.2.9 LV Steelwork

LV pole-mounted equipment including voltage regulators, static balancers, metalclad
fusegear, street lighting brackets, CNE cable sheaths, SNE cable sheaths and armours shall
be bonded to the neutral earth conductor using the bonding conductor detailed in 7.2.4.

Reel insulator supports, pole bolts, D-irons and stay make-offs do not require bonding.

7.2.10 Anti-Climbing Device
The anti-climbing device shall not be bonded to any other steelwork or connected to earth.

7.2.11 Stays

All stays attached to a pole shall have a fully rated insulator or insulator(s) fitted in the stay in
accordance with the Overhead Line manual. This is to prevent the bottom of the stay
becoming live in the event of a pole-top insulation failure.

• HV stays: the pole-top make-off of all HV stays shall be bonded to the steelwork in
accordance with the Overhead Line Manual.

• LV stays: the pole top make-offs of LV stays shall not be bonded to the steelwork.

© UK Power Networks 2014 All rights reserved Page 28

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3 Earthing Arrangements

The standard earthing arrangements detailed in this section satisfy the design principles and
earthing requirements outlined in the previous sections and include the following:

• Pole-mounted transformers with LV overhead line and LV cable.
• Switches, reclosers and sectionalisers.
• Handle-operated air-break switch disconnectors.
• Hook-stick operated equipment.

Note: The arrangements demonstrate the earthing principles but should be constructed in
accordance with the Overhead Line manual.

7.3.1 Pole-Mounted Transformer with HV Overhead Line and LV Overhead Line

All Steelwork L Transformer Key:
Connected to N Earth Covered Aluminium
HV Earth Terminal Earth Conductor
L1 Covered Copper Earth
HV Earth L2 LV Network either Conductor
L3 ABC or Open Wire Bare Earth Conductor
Bi-metallic Splice N Phase Conductor
Neutral Conductor
(100mm below lowest crimp) Bare LV Overhead Line

Insulated for a Note: Anti-climbing
Minimum of 3m Guards Not Shown
Above Ground Level
Mechanical LV Earth
Protection for a
Minimum of 2m Bi-metallic Splice

Bi-metallic Splice (150-300mm above ground)

(150-300mm above ground)

Ground Level

1m Min 8m Separation
2.4m min

HV Earth Electrode LV Earth Electrode
(to achieve max 10Ω) (to achieve max 20Ω)

© UK Power Networks 2014 All rights reserved Page 29

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.2 Pole-Mounted Transformer with HV Overhead Line and LV Cable

All Steelwork L Key:
Connected to N Covered Aluminium
HV Earth Earth Conductor
Covered Copper Earth
HV Conductor
Earth Bare Earth Conductor
Bi-metallic Splice Phase Conductor
Neutral Conductor
(100mm below lowest crimp)
Note: Anti-climbing
Insulated for a Guards Not Shown
Minimum of 3m
Above Ground Level Transformer
Mechanical Earth Terminal
Protection for a
Minimum of 2m LV
Earth
Bi-metallic Splice
Bond to LV CNE
(150-300mm above ground) Cable Shealth
LV CNE Cable
(PVC Covered)

Bi-metallic Splice

(150-300mm above ground)

Ground Level

1m 2.4m min 8m Separation

HV Earth Electrode LV Earth Electrode
(to achieve max 10Ω) (to achieve max 20Ω)

Note: Where a metallic sheathed hessian served LV cable is connected to a pole-mounted
transformer the cable shall be replaced with a plastic sheathed cable for a minimum length of
8m to ensure HV/LV earth segregation is maintained..

© UK Power Networks 2014 All rights reserved Page 30

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.3 Handle-Operated Air-Break Switch Disconnector (ABSD)

HV Key:
Earth
Covered Aluminium
Earth Conductor
Covered Copper Earth
Conductor

Bare Earth Conductor

All Steelwork
Connected to
HV Earth

Bi-metallic Splice

(100mm below lowest crimp)

Operating Rod
Insulator

Switch Insulated for a Minimum of
3m Above Ground Level
Handle
Mechanical Protection for
Earth a Minimum of 2m
Mat
Bi-metallic Splice

(150-300mm above ground)

Ground Level

2.4m minPVC
1mDuct
Installe
300m m d from
Pole to
Earth
Rod

5m Separation HV Earth Electrode
Plan View (to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 31

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.4 Handle-Operated Air-Break Switch Disconnector (ABSD) with Cable Termination

HV Key:
Earth
Covered Aluminium
Earth Conductor

Covered Copper Earth
Conductor

Bare Earth Conductor

All Steelwork
Connected to
HV Earth

Bi-metallic Splice

(100mm below lowest crimp)

HV
Cable

Operating Rod

Insulator Insulated for a Minimum of 3m Above Ground Level

Switch Mechanical Protection for a
Handle Minimum of 2m

Bi-metallic Splice

(150-300mm above ground)

Ground Level

Earth 2.4m minPVC Duct
Mat 1mInstalled
from Pole to
300m m Earth Rod

5m Separation HV Earth Electrode
Plan View (to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 32

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
7.3.5 Hook-Stick Operated ABSD Date: 28/07/2014

All Steelwork
Bonded Together
Key:
Covered Copper Earth
Conductor

Ground Level

© UK Power Networks 2014 All rights reserved Page 33

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.6 Hook-Stick Operated ABSD with Cable Termination (including Surge Arresters)

HV Key:
Earth
Covered Aluminium
Earth Conductor

Covered Copper Earth
Conductor
Bare Earth Conductor

All Steelwork
Connected to HV
Earth

HV

Cable
Bi-metallic Splice

(100mm below lowest crimp)

Insulated for a Minimum
of 3m Above Ground
Level

Mechanical Protection
for a Minimum of 2m

Bi-metallic Splice

(150-300mm above ground)

Ground Level

PVC Duct Installed
from Pole to Earth Rod
2.4m min
5m Separation 1m

HV Earth Electrode
(to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 34

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.7 Hook-Stick Operated Equipment with a Pole-Mounted Transformer

Key: All Steelwork Fuses
Connected to or Links
Covered Aluminium HV Earth
Earth Conductor

Covered Copper Earth
Conductor
Bare Earth Conductor
Phase Conductor
Neutral Conductor

Note: Anti-climbing L
Guards Not Shown Transformer

HV N Earth
Earth Terminal

Bi-metallic Splice LV
Earth
(100mm below lowest crimp)

Insulated for a Minimum of Bond to LV CNE
3m Above Ground Level Cable Shealth
Mechanical Protection for a LV CNE Cable
Minimum of 2m (PVC Covered)
Bi-metallic Splice
Bi-metallic Splice
(150-300mm above ground)
(150-300mm above ground)
Ground Level
1m 2 4m. min PVC Duct Installed from
LV Earth Electrode
Pole to Earth Rod (to achieve max 20Ω)

5m Separation
min 8m Separation

HV Earth Electrode
(to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 35

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
7.3.8 Cable Termination (including Surge Arresters) Date: 28/07/2014

Key: All Steelwork
Connected to
Covered Aluminium HV Earth
Earth Conductor

Covered Copper Earth
Conductor
Bare Earth Conductor

Bi-metallic Splice HV
Cable
(100mm below lowest crimp)
Ground Level
HV
Earth

Insulated for a Minimum of
3m Above Ground Level
Mechanical Protection for a
Minimum of 2m

Bi-metallic Splice

(150-300mm above ground)

1m 2.4m min

HV Earth Electrode
(to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 36

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.9 Pole-Mounted Switches, Reclosers and Sectionalisers with Low-level Control Unit

Direction of Supply

Key:
Covered Aluminium
Earth Conductor

Covered Copper Earth
Conductor
Bare Earth Conductor

Bi-metallic Splice

(100mm below lowest crimp)

HV
Earth

30 Ground Level
0 Earth Mat
m
m

m
4m i

.2 n

HV Earth Electrode
(to achieve max 10Ω)

Plan View

© UK Power Networks 2014 All rights reserved Page 37

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

7.3.10 Pole-Mounted Switches, Reclosers and Sectionalisers with High-level Control Unit

Direction of Supply

Key: All Steelwork
Covered Aluminium Connected to
Earth Conductor HV Earth

Covered Copper Earth Note: VT Neutral
Conductor Earth Not Shown
Bare Earth Conductor

Note: Anti-climbing
Guards Not Shown

Bi-metallic Splice

(100mm below lowest crimp)

HV
Earth

Insulated for a Minimum of Ground Level
3m Above Ground Level
Mechanical Protection for a1m 4m.2 min
Minimum of 2m

Bi-metallic Splice

(150-300mm above ground)

Ground Level

PVC Duct Installed
from Pole to Earth Rod

5m Separation

HV Earth Electrode
(to achieve max 10Ω)

© UK Power Networks 2014 All rights reserved Page 38

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

8 LV Earthing

This section provides an overview of the main LV earthing requirements; refer to EDS 06-
0016 for further information. Appendix B includes the definitions of the various LV earthing
system types.

8.1 Design Overview

All new low voltage mains and services shall be constructed to PME standards using
combined neutral earth (CNE) cables and overhead lines to enable an earth terminal to be
provided. Whenever major work (e.g. refurbishment, diversion etc.) is carried out on the low
voltage distribution network it shall be brought up to PME standards where appropriate.

8.2 Installation Requirements

8.2.1 Additional PME Electrodes

In addition to the main LV neutral earth at or near the secondary substation or pole-mounted
transformer, the neutral conductor shall be connected to earth (using the electrode specified
in Section 8.2.2) as follows:

• All pot-ends on underground cable networks.
• All cut-outs above 100A for large services and multi-occupancy buildings. Note: The

earth is usually placed in the cable trench outside the building.
• Not more than every six spans on LV overhead line networks.

Note: Earth electrodes shall not be installed in any joint.

8.2.2 Earth Electrodes

The permitted earth electrodes are given below.

Note: The use of rod electrodes is preferred but due to practical difficulties, particularly in
urban areas where damage can be caused to other services, cable electrodes are
acceptable.

Cable Size Underground Cable Network Overhead Network
Up to
35mm2 1.2m earth rod connected via 35mm2 1.2m earth rod connected via 35mm2
covered copper cable or 2m of 35mm2 covered copper cable (below ground) and
> 35mm2 95mm2 covered aluminium cable (above
bare copper cable laid directly in trench ground)
underneath the LV cable 1.2m earth rod connected via 70mm2
1.2m earth rod connected via 70mm2 covered copper cable (below ground) and
covered copper cable or 2m of 70mm2 95mm2 covered aluminium cable (above
ground)
bare copper cable laid directly in trench
underneath the LV cable

© UK Power Networks 2014 All rights reserved Page 39

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

8.2.3 Bonding Conductors

The minimum size of bonding connections are given below. Below ground, i.e. buried,
earthing and bonding conductors shall be copper. Above ground bonding conductors may be
copper, aluminium or corrosion protected steel of the appropriate cross sectional area.

Connection Type Bonding Conductor

Between supply neutral conductor and PME For cable sizes up to 35mm2: 50mm2 covered
earth electrode aluminium cable or 35mm2 covered copper
cable
Between supply neutral conductor and link box For cable sizes greater than 35mm2: 95mm2
or feeder pillar steelwork covered aluminium cable or 50mm2 covered
copper cable
Between sheath of SNE cable and neutral of
CNE cable 16mm2 or half the size of the neutral meter tail,
whichever is the larger.
At customer’s premises between service neutral
and main earthing terminal Note: This is usually built into the cut-out
16mm2 or half the size of the neutral meter tail,
At customer’s premises between the main whichever is the larger
earthing terminal and the earth bar of the
consumer unit

Note: The bonding between the main earthing
terminal and the consumer unit is the
responsibility of the consumer. It is given here
for information only.

8.2.4 Earth Resistance Values

The resistance of the supply neutral conductor to the general mass of earth shall not at any
point exceed 20Ω. This can be achieved using the values below.

Electrode Resistance Value Electrode Systems
Main LV Earth 20Ω Refer to Section 10 and 11
Additional PME Earth 100Ω

© UK Power Networks 2014 All rights reserved Page 40

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

8.2.5 Converting Existing Underground Cable Networks to PME

The opportunity shall be taken wherever possible to upgrade existing networks to PME. Any
extension or modification shall use CNE cables and their typical application to existing
networks is shown below.

S/S CNE Key:
SNE
SNE S/S
SNE Secondary substation
See note 2
S/S LB
CNE See note 1 Link box

S/S CNE SNE SNE Separate neutral and earth cable
SNE
See note 2 CNE Combined neutral and earth cable
S/S Transition joint – CNE neutral
CNE SNE See note 1 connected to SNE neutral and shealth

S/S PME earth electrode
LB SNE
Meets PME requirements
New CNE Service
Notes:
S/S SNE 1. A non-insulated SNE cable in direct contact
SNE with the ground will usually provide an adequate
earth electrode.
See note 2
2. These sections of SNE cable will meet the
See note 1 PME requirements if the sheath and neutral are
bonded at the end of main and an end of main
electrode added.

All reasonable precautions shall be taken to ensure that customers supplied via SNE cables
are not adversely affected by repairs, modifications or additions to existing networks. When
a CNE cable is introduced into a SNE network, existing customers may retain a SNE service
provided:

• A continuous metallic earth return path exists to the source substation; and
• They are connected to a continuous length of non-insulated metallic sheathed cable in

direct contact with the ground with an earth resistance of 10Ω or less. The table below
specifies the length required to achieve this in different soil conditions.

If these conditions cannot be satisfied the service shall be converted to PME (provided the
installation complies with the BS 7671 bonding requirements), or a TT earthing system shall
be used.

Typical Soil Type Resistivity (Ωm) Length (m)

Loams, garden soils etc. 25 or less 8
Chalk 50 or less 15
Clay 100 or less 29
Marsh/Peat 200 or less 58
Sand/Gravel/Clay mix 300 or less 87
Slate/Shale/Rock 500 or less 115

© UK Power Networks 2014 All rights reserved Page 41

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

8.2.6 Converting Existing Customers to PME

Customers with an existing separate neutral and earth, connected to an SNE cable network
can be converted to a combined neutral and earth (PME) provided the following
requirements are satisfied:

• The customer's installation complies with BS 7671.
• A new PME cut-out is installed.

• The SNE cable is replaced with a CNE cable (or the neutral and earth are combined at
the service transition joint and at the cut-out).

• An earth electrode is required at the service transition joint. However a length of SNE
cable in direct contact with the ground will normally provide a suitable connection with
earth and satisfy this requirement.

Note: It is not permitted to simply bond the neutral and earth at the cut-out.

8.2.7 Protective Neutral Bonding (PNB)

Although PME is preferred, protective neutral bonding (PNB) may provide a better solution in
circumstances where it is not practical to install the LV earth at the transformer. In a PNB
earthing system the LV neutral conductor is connected to an earth electrode at a point
remote from the transformer at or near the customer's supply terminals. PNB arrangements
may only be used if the following criteria are satisfied:

• A maximum of four customers.
• The connection to earth shall be made as close as possible to customer's supply

terminals and no more than 40m from the furthest customer.
• The earth electrode shall have a maximum resistance of 20Ω.
• The earth electrode shall be a minimum of 8m from any HV earth or HV metallic sheath

cable.
• The metallic sheaths of any LV cables shall also be connected to the earth electrode at

the customer’s supply terminals and to the LV neutral at the transformer.
• The transformer tank and associated HV metalwork shall be connected to the HV earth

electrode.
A PNB earth terminal shall be treated as a PME earth terminal and the appropriate
labelling from Section 14 applied (EDS 07-0009.121 and EDS 07-0009.9).

Various PNB earthing arrangements are shown below.

HV : LV HV : LV

HV : LV CNE Cut-out CNE Cut-out
HV : LV HV : LV

SNE Cut-out SNE Cut-out SNE Cut-out

© UK Power Networks 2014 All rights reserved Page 42

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

9 Customer Installations

9.1 Earth Terminal

A PME earth terminal can usually be offered to customers, except in special situations,
provided their installation complies with BS 7671. Customer installations including special
situations and the provision of a PME earth terminal are covered in more detail in EDS 06-
0017. The earth terminal shall only be provided as detailed in the design and it shall have the
appropriate labelling from Section 14 applied (EDS 07-0009.130 and.9).

9.2 Connection to Supply Neutral Conductor at the Cut-out

If an earth terminal is being provided the customer's earth terminal shall be connected to the
supply neutral terminal/conductor for CNE services or the earth terminal/conductor for SNE
services at the cut-out using a copper conductor with a minimum cross-sectional area as
specified in Section 8.2.3. Any bolted link between the neutral and the earth terminal shall be
of equivalent cross-sectional area.

9.3 Connection to Cable Sheath/Armouring at the Cut-out

The metallic sheath and armouring of underground service cables shall be connected to the
earth terminal by means of a copper conductor of minimum cross-sectional area as specified
in Section 8.2.3. The connection to the cable sheath should be made by means of either an
approved earthing clamp or a substantial sweated connection in accordance with the LV
Cable Jointing manual.

Where service cables with a concentric neutral are used, the concentric neutral and any
separate earth conductor shall be connected to the earth terminal, neutral terminal or neutral
connector block, as appropriate.

9.4 Earth Fault Loop Impedance

Typical earth fault loop impedance values are shown below. For further information refer to
EDS 06-0004 which also includes a flowchart to resolve situations where these values
cannot be achieved and a dedicated form (UPN9017) to advise customers.

Earth Terminal 230V 1Ø 400V 3Ø 400V 3Ø 400V 3Ø

Up to 100A Up to 100A 200 to 300A Exceeding 300A

PME/PNB 0.35Ω 0.35Ω 0.2Ω 0.15Ω
0.8Ω
Cable Sheath/Continuous Earth Wire 0.8Ω

© UK Power Networks 2014 All rights reserved Page 43

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

10 Earth Electrode Options

The table below provides the resistance of varying lengths of earth rod based on the soil
resistivity. For example a 6m rod in 100Ωm soil will give a resistance of 18.6Ω .

If multiple rods are used and separated by the twice the rod length, the approximate
resistance can be found by dividing the resistance of a single rod by the number of rods. For
example four 6m rods spaced 6m apart will give an approximate resistance of 18.6/4 ≈ 5Ω.

No of Rod Length Resistance (Ω)

Rods (m) 25Ωm 50Ωm 100Ωm 150Ωm 200Ωm 300Ωm 400Ωm 500Ωm

1 1.2 17.9 35.8 71.6 107.4 143.2 214.7 286.3 357.9
2 2.4 10.1 20.2 40.4 60.6 80.8 121.2 161.5 201.9
3 3.6 7.2 14.4 28.7 43.1 57.4 86.1 114.9 143.6
4 4.8 5.6 11.2 22.5 33.7 45.0 67.5 90.0 112.5
5 6.0 4.6 9.3 18.6 27.9 37.2 55.8 74.3 92.9
6 7.2 4.0 7.9 15.9 23.8 31.8 47.7 63.6 79.5
7 8.4 3.5 7.0 13.9 20.9 27.8 41.7 55.6 69.6
8 9.6 3.1 6.2 12.4 18.6 24.8 37.2 49.6 62.0
9 10.8 2.8 5.6 11.2 16.8 22.4 33.6 44.8 56.0
10 12 2.6 5.1 10.2 15.3 20.4 30.6 40.8 51.1
11 13.2 2.3 4.7 9.4 14.1 18.8 28.2 37.6 47.0
12 14.4 2.2 4.4 8.7 13.1 17.4 26.1 34.8 43.6
13 15.6 1.9 3.8 7.7 11.5 15.4 23.1 30.8 38.5
14 16.8 1.8 3.6 7.2 10.9 14.5 21.7 28.9 36.2
15 18 1.8 3.6 7.2 10.7 14.3 21.5 28.7 35.8
16 19.2 1.7 3.4 6.8 10.2 13.5 20.3 27.1 33.9
17 20.4 1.6 3.2 6.4 9.6 12.8 19.3 25.7 32.1

The table below provides the resistance of varying lengths of 70mm2 copper earth conductor

buried at a depth of 0.6m and a lattice earth mat based on the soil resistivity. For example, in
100Ωm soil a 50m conductor will give a resistance of around 3.9Ω or a 1m x 1m earth mat
embedded in an earthing compound will give a resistance of around 14.66Ω.

Conductor/Mat 25Ωm Resistance (Ω)
Length 3.6 50Ωm 100Ωm 150Ωm 200Ωm 300Ωm 400Ωm 500Ωm
1.8
10m 1.0 7.3 14.6 21.9 29.2 43.8 58.3 72.9
3.5 7.0 10.5 14.0 21.0 28.0 35.0
25m 0.5 2.0 3.9 5.9 7.9 11.8 15.8 19.7

50m 0.4 1.1 2.2 3.3 4.4 6.6 8.8 11.0

Conductor 100 0.3 0.8 1.5 2.3 3.1 4.6 6.2 7.7
m
0.2 0.6 1.2 1.8 2.4 3.6 4.8 6.0
150 13.2
m 0.5 1.0 1.5 2.0 3.0 4.0 5.0
3.7 26.3 52.6 79.0 105.3 157.9 210.6 263.2
200
m 7.3 14.7 22.0 29.3 44.0 58.6 73.3

250
m

1m x 1m Lattice Mat in
Soil

1m x 1m Lattice Mat in
Earthing Compound

© UK Power Networks 2014 All rights reserved Page 44

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

11 NetMap Earthing Information System

NetMap4 includes several earthing maps showing the earthing options to achieve 1Ω, 10Ω
and 20Ω earths. Brief details are shown below. For further information refer to EDS 06-0018.

The earthing maps are selected using the
Object Control as shown. The various
maps can be displayed by clicking the
following buttons:

1 ohm earthing map.

10 ohm earthing map.

20 ohm earthing map.

An example of the 20Ω map and its associated properties (select area of map, right-click and
select Edit Selection) is shown below. The map colour and traffic light provides a quick
indication of the type of earthing installation required and the properties provide additional
details.

4 NetMap is UK Power Networks GIS system. Page 45
© UK Power Networks 2014 All rights reserved

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

12 Materials

The most common earthing materials are listed below and a more extensive list can be
found in EAS 06-0011.

Component Description Material Code5
Earth rods Earth rod extensible 1.2m x 19mm 02472U
Earth rod coupling 02475Y
Earth 02473E (standard) 02478D (special)6
mat/grate Earth rod driving stud 02479N
Earth Earth rod driving point 03100V
electrode Copper lattice earth mat 1m x 1m Not available see EAS 06-0011 7
Galvanised earth grate
70mm2 Bare stranded (7/3.55mm) hard 05823E
drawn copper cable (to BS 7884)
25mm x 3mm 25mm x 6mm
Bare copper tape (to BS EN 13601) 02998J 03008R

Bonding PVC covered stranded soft drawn copper 16mm2 35mm2 70mm2 120mm2
cable (to BS 6004) 05847L 05864Y 05865J 05867D
Bonding PVC covered stranded aluminium cable 35mm2 50mm2 95mm2 120mm2
(above
ground only) 40mm x 6mm Bare aluminium tape/bar 06209E 06210A 06211K 06212U

Tape 25m Coil Bar 4m Length
03004C 01303G

80mm aluminium lap joint 01629F
Aluminium right angle fishplate
01630B
40mm x 6mm plastic cleat self-locking
22mm2 tinned copper braid 01619W
Earth bar 6-way with M10 studs
Earth Bar Earth rod U bolt clamp 03095Q
Connectors NE13 brass connector 02477T

Brass Mechanical lug M10/M12 02476J 120mm2
02236J
Tinned copper compression lug M10/M12 02829A 70mm2 120mm2
16mm2-70mm2 01372H 01373S
02228U

35mm2 50mm2
02365H 02364X

Bimetallic splice (copper/aluminium) 01354K 01371X 08421S 09023L
35mm2 /50mm2 70mm2 /120mm2
Rebar clamp for 20-25mm rebar
2-hole earth point with 1500mm welded tail 09891N 08683E
Consumables Castrol Rustilo 431 grease
Denso tape 50mm x 10m 01351F
Marconite earthing compound 25kg bag
01353A (for use with the above)

Not available see EAS 06-0011

03452G

03132R

5 UK Power Networks logistics material code.
6 The special earth rod driving stud (02478D) is supplied as an alternative drive head where the standard earth
rod driving head (02473E) is too large to fit into existing installation tools.
7 Material currently being sourced and will be added to the stores catalogue, EAS 06-0011 will be updated when
available.

© UK Power Networks 2014 All rights reserved Page 46

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

13 Connection Techniques

The table below outlines the approved bolted, mechanical and crimped connections for
earthing; exothermic welded or brazed connections are also acceptable. Refer to ECS 06-
0022 for all other approved connection techniques not included below.

Application Connection Technique

Copper conductor to
earth rod using U-bolt
clamp

Copper conductor to
copper conductor using
NE13 connector

Earth rod 02472U and U-bolt clamp 02476J Sicame NE13 02829A

Copper conductor to
reinforcement rebar and
mesh

U-bolt clamp 02476J on Earth point with tail 01353A U-bolt clamp 02476J on
Rebar mesh

Conductor connection to
6-way Earth Bar
(02477T) using lug

Copper conductor to
aluminium conductor or
tape using a bimetallic
crimps (09891N or
08683E) and lugs
(various)

Bimetallic crimp 09891N Aluminium tape 50mm x 6mm 03005M, clip
to wall 01620S and bimetallic lug 02228U

© UK Power Networks 2014 All rights reserved Page 47

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

Application Connection Technique No Substation Earth Ring
LV Board
Substation Earth Ring Installed Connect the neutral on the LV
board to the main earth terminal
Connect the neutral on the LV using 120mm2 covered copper
board to the substation earth ring cable. A short length of 40mm x
using 40mm x 6mm aluminium bar 6mm aluminium bar may be
attached to the neutral to facilitate
the connection

Earth link in pit (for
segregation of customer
earthing systems) using
earth test pit and copper
tape (02998J or 03008R)

Fence panel/post
bonding

Tape to tape Exothermic welded or bolted connections in accordance with
ECS 06-0022
Equipment connections Mechanical lugs
HV cables Refer to the 11kV Cable Jointing manual
LV cables Refer to the LV Cable Jointing manual
Overhead Lines Refer to the Overhead Line Manual

Notes:

• All surfaces shall be cleaned before jointing.
• All connections to metalwork shall be free from paint, cleaned and have a protective

coating of neutral compound grease8 applied before and after connection.

• All below ground connections shall be completely covered in Denso tape to prevent
moisture ingress and corrosion

• All joints involving dissimilar metals (e.g. copper and steel, copper and aluminium) shall
be 100mm above ground level and completely covered in Denso tape to prevent
moisture ingress and corrosion.

© UK Power Networks 2014 All rights reserved Page 48

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023

Version: 4.0

Date: 28/07/2014

8 The use of neutral compound grease is particularly important for aluminium bolted joints to prevent surface
oxidation and corrosion.

© UK Power Networks 2014 All rights reserved Page 49

Secondary Distribution Network Earthing Construction Document Number: ECS 06-0023
Version: 4.0
Date: 28/07/2014

14 Warning Labels

Situation/Location Reference9 Specification Label

(Material Code10)

Separate HV and LV EDS 07-0009.118 100mm x 50mm

Earths adhesive label

In LV cabinet or
micro/compact

Separate HV and LV EDS 07-0009.117 170mm x 220mm
Earths (21515D) ABS sheet

Install in prominent
position inside
fence/enclosure

PME/PNB Earth EDS 07-0009.130 100mm x 50mm
Next to the cut-out
(21758H) adhesive label

PNB Earth EDS 07-0009.9 70mm x 20mm tie
on label
On the PNB earth
where it enters the EDS 07-0009.120 100mm x 50mm
cut-out adhesive label

Two Earthing
Systems

At the removal link
between connecting
two separate
earthing systems

HOT Sites Refer to EDS 06-0121 for a complete set of HOT site labels

9 Refer to EAS 07-0021 for the availability of labels without a material code. Page 50
10 UK Power Networks logistics material code.
© UK Power Networks 2014 All rights reserved