Fencing Specification for Substations

Version: 2 Date of Issue: July 2009
Author: Keith Nutter Job Title: Civil Engineer
Approver: Mark Simpson Job Title: Network Standards Manager
Specification
Fencing for Grid, Primary
and Secondary
Distribution Substations

Specification for Fencing for Grid, Primary and Secondary Substations
Version: 2.0 Date of Issue: July 2009 Page 2 of 13
The master version of the this document resides in the E.ON UK Documentum database
CAUTION – any other copy may be out of date
© Central Networks plc
Revision Log
Version:
2.0 Prepared
by:
Keith Nutter Date: July 2009
Version:
2.0
DRAFT
Prepared
by:
Keith Nutter Date: May 2009
Draft
Update
Version: 1.0
Prepared
by:
Keith Nutter Date:
November
2006
First Issue
Version: 0.2
Prepared
by:
Keith Nutter Date: May 2006
Revised draft
Version: 0.1
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Keith Nutter Date: January 2006
Draft

CONTENTS
1. INTRODUCTION 4
2. SCOPE 4
3. FENCING OPTIONS 4
3.1 GENERAL 4
3.2 GRID AND PRIMARY SUBSTATIONS 5
3.3 DISTRIBUTION SUBSTATIONS 5
3.4 PADMOUNT SUBSTATIONS 6
4. SPECIFICATION FOR FENCING 7
4.1 STEEL PALISADE FENCING 7
4.2 STEEL MESH FENCING 9
4.3 BRICKWORK WALLS 9
4.4 TIMBER FENCING 10
4.5 OTHER FENCING 11
4.6 CONSTRUCTION DETAILS 11
4.7 FENCE EARTHING 12

1. INTRODUCTION
The Electricity Supply, Quality and Control Regulations 2002, in paragraph 11, place a
requirement on every generator and distributor for every substation they own to:
(a) enclose the substation where necessary to prevent, so far as is reasonably
practicable, danger or unauthorised access;
(b) enclose any part of the substation, which is open to the air and contains live
equipment which is not encased, with a fence or wall not less than 2.4 metres in
height to prevent, so far as is reasonably practicable, danger or unauthorised
access.
This policy sets out Central Network’s methodology for complying with the above
requirements, and for provide a durable, low maintenance fencing solution at substations.
2. SCOPE
This policy applies to all Central Networks Grid, Primary and Distribution substations. In
addition this policy can be applied where fencing is needed around other operational assets
such as overhead line towers and reserved substation sites.
3. FENCING OPTIONS
3.1 GENERAL
It is important that the standard of fencing provided matches the perceived risk rating of the
site. An assessment must be made of each site to determine potential security hazards,
relating to location of the substation and adjacent land use. Particular attention must be paid
to the possibility of the storage of items immediately outside the fence, which would reduce
the effectiveness of the fence.
Following an incident in the 1980’s the Selston Report, ‘Child Trespass in Electricity
Substations (1986)’, recommended that substation boundaries should give visibility into the
substation to enable any trespassers to be seen. Where possible this requirement must be
incorporated into substation fence construction. As an example, there may be a need to use
a timber close boarded fence at a distribution substation, but the gates should if possible be
of open mesh construction to enable visibility into the substation.
In all cases the objective is to achieve a durable, low maintenance fencing that meets the
security needs of the site. In addition locking arrangements, possible footholds and climbing
aids, type of gates and hinges must be considered to maximise the security of the fencing
provided.

3.2 GRID AND PRIMARY SUBSTATIONS
Grid and Primary substations will usually include two separate fences, a Security Fence
immediately surrounding the live equipment, and a Boundary Fence to mark the extent of our
site area.
The Security Fence will generally be a 2.4 metre high Steel Palisade fence to the
specification detailed below. Where possible the security fence must be inset from the
boundary of the site to allow access around the fence for maintenance. In addition this will
also permit a boundary fence to be erected which will reduce problems from material storage
against the security fence. A minimum inset distance of two metres is required. Very
occasionally a higher palisade fence may be required to ensure satisfactory security of the
site, or alternatively additional anti climbing measures such as razor wire may be used.
When planning the layout of the security fence care should be taken to avoid external angles
of 90 degrees or less. These tight angles are considered to increase the risk of persons
gaining entry over the fence as the two adjacent panels can be used to aid climbing. If such
angles cannot be avoided then additional anti climb measures, such as barbed wire, razor
wire or spinners shall be provided at these corners.
The boundary fence construction should where possible be a steel mesh fence to the
specification detailed below. However there may be instances where factors such as
Planning Permission direct that alternative materials must be used. In these instances a
timber post and rail, timber close boarded, brickwork wall or post and wire fence may be
used. In each case the fence type must comply with the appropriate specification.
The preferred height of boundary fence is 1.8 metres, but there may be instances where 1.5
metre or 1.2 metre heights is used to meet local requirements. In a few ‘high risk’
environments the boundary fence may also be a 1.8 metre or 2.4 metre steel palisade fence.
3.3 DISTRIBUTION SUBSTATIONS
New distribution substations will normally be housed in a GRP or Masonry housing. In these
cases there is no requirement for a boundary fence, but the extent of our plot of land should
be identified with boundary markers.
There will be a few instances where new ‘outdoor’ substations are provided, and there will be
many instances where replacement fences are needed to outdoor sites. In these cases the
following rules shall apply:
The majority of outdoor distribution substations will have a single fence located on the
boundary of our property. Again consideration must be given to the appropriate risks
including adjacent land use.
The preferred fence type is a 1.8 metre high steel mesh fence with steel posts. For certain
locations such as garage block areas it will be beneficial to use a 1.8 metre steel palisade
fence. The heavier construction of steel palisade is more resistant to vehicle damage. Again
for a few ‘high risk’ sites 2.4 metre steel mesh, or 2.4 metre steel palisade may be needed.

As with Primary substations there will be some sites where Planning Permission, or issues,
prevent the use of steel mesh or steel palisade fences. In these cases a variety of solutions
are possible including brickwork walls, timber close boarded fencing or concrete panel
fencing. The exact choice will depend on either planning requirements, stated fence types in
the site legal documents, or on local environment requirements.
Of the above alternatives the preferred solution is timber close boarded fence. Where
possible, gates should be of mesh construction to allow visibility into the substation.
3.4 PADMOUNT SUBSTATIONS
In some locations Padmount substations are installed as an alternative to the standard
distribution substation. The Padmount Application Guide requires the provision of a timber
fence around the padmount in some circumstances. See the Padmount Application Guide
for full details. The timber fence used shall be a close boarded design, with timber posts,
rails and boards.
The fencing requirements can therefore be summarised as:
Substation Type ‘Normal’ Risk Installations ‘High Risk’ Installations
Grid and Primary Substations
Security Fence around live equipment 2.4m Steel Palisade Usually 2.4m Steel Palisade
Consider 3.0m Steel
Palisade or additional anti
climbing measures for
certain high risk sites
Boundary Fence 1.8m Steel Mesh Fence Usually 1.8m Steel Mesh
but consider upgrade to
1.8m or 2.4m Steel Palisade
for certain sites
Distribution Substations
Single Fence Situations – no
restrictions
1.8m Steel Mesh Fence Consider 2.4m Mesh fence,
1.8m or 2.4m Steel Palisade
for sites with higher risk of
trespass or risk of vehicle
damage
Single Fence Situations – with
restrictions
For sites where Planning,
Legal or Local Environment
conditions do not allow Steel
Mesh or Steel Palisade,
consider timber, brickwork or
concrete panel fencing. Of
these Timber Close Boarded
is preferred (with mesh gates)
Not applicable
Padmount Substations
See Padmount Application Guide Timber close boarded fence Not applicable

4. SPECIFICATION FOR FENCING
4.1 STEEL PALISADE FENCING
4.1.1 Design
General
The design specification is based on, but to a higher standard than, BS1722 Part 12: 2006
Specification for Steel Palisade Fences.
The standard security fencing for Grid and Primary substations is 2.4 metre high steel
palisade. Fencing and gates shall comply with the details shown on the drawings listed
below. The 2.4m height is measured from the top of the kerb to the top of the fence, as
shown on the drawing. Actual pale length is 2.37m In addition there should be a nominal
distance of 60mm between the top of the kerb and ground level, on the outside of the fence.
On some sites an additional electric fence will be required, fixed to the back of the normal
security fence. These sites will be individually assessed by Network Standards. Where an
electric fence is required the necessary fixings shall be incorporated into the design and
fabrication of the standard security fence.
Where large plant items such as transformers are present then removable fence posts shall
be provided to aid installation and removal of the plant.
Any items such as safety notices, substation nameplates, drawbolt handles, and locking
mechanisms, must be designed and positioned so as to prevent a foothold which would
assist in gaining access over the fence or gates. In particular, danger of death notices
should usually be positioned such that the top fixing is just above the top rail of the fence.
This positions the notice so it is not a climbing aid and prevents the notice slipping down the
fence pales.
Components and Fixings
Pales are to be nominal 3.0mm 'W’ section as shown on drawing STND/408/001. Other
types of pale are only to be used where specifically requested (generally where required to
match existing fencing). Care must be taken to ensure the pale thickness is to the
specification.
The maximum permitted spacing between adjacent pales, or between pales and posts is
85mm.
Rail to post fastenings are to be 12mm diameter galvanised, grade 8.8, cup square bolts with
grade 8, shear off ‘cone’ type nuts. Connector plates are to be welded to the posts, as
shown on the drawings. Slotted posts with ‘loose’ connector plates are not permitted.
Pale to rail fastenings are to be 8mm diameter sheradised high clench bolt and collar fixings,
or 8mm diameter shaped head bolts with shear off ‘cone’ type nuts. See drawing STND /
408 / 001 for full details. In all applications the head of the fastener should be ‘matched’ to

the pale profile to ensure a good fit, minimising any gap to the underside of the head of the
fastener. This will ensure the risk of the fastener head being chiselled off is minimised.
At junctions with lower height fences, or fences which are easily climbable, raked wing fence
panels shall be used. These panels are to be constructed strictly in accordance with drawing
STND/408/006.
If non standard length fence panels are required, then the rails must be pre-fabricated and
galvanised. Cutting or drilling of any galvanised component will not be permitted. Spacing of
posts should be carefully designed to avoid small make up panels whilst maximising the
number of standard length panels (as an example a gap of 3.5 metres is better filled with 2
panels of 1.75 metres rather than one standard panel and a small make up panel).
Rails are to be connected to posts before pales are fastened to the rails, i.e. pre-assembly
will not be permitted. Welded construction will not be permitted for fencing panels.
Foundations
Post length below ground must be as shown on drawing STND/408/001. Where the length
below ground cannot be achieved, because of cables for instance, then the foundation must
be redesigned to ensure sufficient restraint. In particularly poor ground conditions, or
locations at the top of slopes, the foundation shall be designed to suit the ground conditions.
A continuous concrete kerb, minimum size 250mm wide x 150mm deep, must be provided
beneath the line of the fence. The nominal spacing between the bottom of the pale and the
top of the kerb is 30mm, and this dimension must not exceed 50mm.
Removable post foundations shall be designed to suit the ground conditions. Typical
foundation size will be 900mm by 900mm by 350mm deep (below insitu kerb), with a
continuous 450mm wide by 150mm deep kerb between removable post foundations.
Concrete for foundations and kerbs shall have a minimum cube crushing strength of 25
N/mm2
at 28 days.
Finish
All components of the fence and gates shall be hot dip galvanised after drilling and cutting,
and before assembly. No cutting or drilling of any galvanised component will be permitted.
All sharp edges caused by drips in the galvanising process shall be carefully removed whilst
maintaining the galvanised finish.
Minor accidental damage to galvanising shall be wire brushed and made good with a ‘Zilt’
stick, or zinc rich paint of an approved type. Alternatively damaged components shall be
sent for acid stripping and re-galvanising.
Welded gates shall be thoroughly de-scaled and hot dip galvanised after fabrication. Where
a decorative paint finish is required, this shall be in addition to galvanising.

4.1.2 Drawings
The following drawings are to be used:
STND / 408 / 001A Details of High Security Palisade Fence
STND / 408 / 002 2400 High Security Palisade Double Gates
STND / 408 / 003 2400 High x 1675 Wide Security Palisade Gate Details
STND / 408 / 004 2400 High Security Palisade Double Gates - Hanging Details
STND / 408 / 005 2400 High Security Palisade Double Gates – Locking Plate Details
STND / 408 / 006 Junction of Palisade with Low Height Boundary Fence
4.2 STEEL MESH FENCING
Steel mesh fencing is used as boundary fencing at Grid and Primary substations and is also
the preferred fencing for outdoor Distribution Substations. Fencing must be manufactured in
accordance with BS1722, part 14. The specification is based on the ‘Expamet Electra’
design of fencing manufactured by Expanded Metal Products of Hartlepool using expanded
metal mesh panels. The use of steel mesh fencing is not limited to the Expamet Electra
product, but any alternative must have similar design and materials to the Expamet product.
1.8m high and 2.4m high versions are required to suit particular applications.
The basic design of the fence consists of:
• Expanded metal mesh, type 2089 (do not use other, lighter mesh types).
• Rolled hollow section steel posts at 3.0 metre centres.
• 3 No horizontal steel rails (other designs of fence with 2 rails are not acceptable).
• Mesh secured to posts with steel strips and shear off fixings.
• Concrete gravel board to be used where required to retain substation surfacing.
• Galvanised finish as standard, coloured powder coating is available where required
(RAL6005 – Dark Green).
• Standard gate sizes of 1.0m single and 2.0m double shall be used where possible. Infill
mesh panels shall be used adjacent to gates where necessary to suit existing openings.
• Gates are welded steel hollow section frame with mesh welded to frame, all to Expamet
standard design.
• Gate locking detail must be designed so it does not provide a foothold for climbing.
The Expamet brochure, installation details and specification sheet for Electra give full details
of the requirements for this type of fencing.
4.3 BRICKWORK WALLS
Walls shall be a minimum of 215mm thick, and designed to the relevant standard to meet all
imposed loading conditions, including wind loads. The design may require the use of piers at

appropriate intervals, or thicker walls in some instances. Typical height of brickwork walls
will be 1.8m, but again there may be instances where higher walls are required.
Bricks shall be frost resistant (type FL) and shall be chosen to match adjacent buildings. In
most instances the local Planning Authority will need to be approached to gain approval for
the proposed brick.
A minimum of two courses of class B Engineering bricks shall be provided as a damp proof
course. The use of sheet material DPCs is not permitted as this reduces the stability of the
wall.
A coping consisting of a brick on edge course shall also be provided. Suitable galvanised
straps shall be used to retain the end and corner units of brick on edge copings.
Alternatively a precast concrete coping can be provided for appropriate situations.
Mortar mixes shall be a minimum of class (iii) for the main body of the wall, and a minimum
of class (ii) for the dpc and coping areas. Mortars to BS EN 998-2: 2003.
4.4 TIMBER FENCING
Timber fencing will generally be 1.8m high close boarded fencing. In some instances
alternative heights of 1.2m and 1.5m may be necessary to suit existing environments. Also
there may be very occasional instances where timber post and rail or timber panel fencing
may be used.
Close Boarded Fencing
Close boarded fencing will use pressure treated boards and rails. Boards should be 125mm
wide, have a minimum thickness in the range 6-7mm, and a maximum thickness in the range
15-18mm. Boards shall be erected with a 25mm overlap. Suitable pressure treated timber
cappings shall be provided. Rails shall be 100mm deep by 50mm wide with a 30mm by
30mm chamfer to the top edge to prevent standing water (sloping top is also acceptable).
Boards are to be fixed to rails with galvanised nails.
The preferred post will be a galvanised steel section, either 102mm by 44mm by 7.44kg/m
RSJ or rectangular hollow box section. The posts shall have gusset plates for connection of
the rails. Gusset plates are to be welded to the post prior to galvanising. Existing concrete
or timber posts can be re-used during replacement of boarding or rails (assuming satisfactory
condition), but will not be accepted for new construction. Rails are to be connected to posts
using galvanised coach bolts.
Gate posts are to be box section steel posts with appropriate single gusset plates and gate
fixings as required. Again steelwork is to be galvanised after fabrication.
On some sites gravel boards may be required to retain ground either inside or outside the
substation. Gravel boards shall be Concrete with suitable galvanised fixings. Timber gravel
boards are not acceptable.

For Padmount substations, posts are to be timber. Steel or concrete posts are not to be
used. Rails and boards are to be timber, to the specification quoted above for general timber
fencing. See Padmount Application Guide for layout of the fencing.
Post and Rail Fencing
Post and Rail fences shall be designation MPR 11/4 to Table 1 of BS1722-7: 2006 with 4
rails and alternate morticed and prick posts. Morticed posts shall be spaced at 2.85 metre
centres. Prick posts shall be placed in the centre of each bay between morticed posts.
Morticed posts shall be set directly in the ground and surrounded by suitable well rammed
backfill. Concrete backfill is not required except where the backfill available is not suitable
for supporting the post.
Timber shall be suitably preserved to give a life expectancy of 15 years as stated in BS 8417.
Central Networks prefer not to use timber treated with creosote or chromated copper
arsenate (CCA) preservative and would prefer to use more environmentally friendly
alternatives such as Tanalith® E and related Copper Azole based preservatives.
4.5 OTHER FENCING
In some locations other fence types may be needed to meet local requirements. These may
include steel chain link fencing, concrete panel fencing, or other ‘architectural’ fences. In
each case the objective is to provide a secure, robust low maintenance design.
Further guidance on the design application and construction of these fence types can be
obtained from Network Standards.
4.6 CONSTRUCTION DETAILS
Locations of all cables must be determined on site prior to work commencing. The position
of the cables may determine the post positions, and therefore the panel lengths.
The fence layout should be optimised to reduce the number of non standard fence panels
where possible (see also 4.1.1 above). For sloping sites levels shall be calculated to ensure
an even gradient is achieved where possible. Care must also be taken to ensure the
effective minimum fence height is achieved on sloping sites; for slopes in excess of 1 in 10 a
higher than standard fence will be required.
Concrete for foundations and kerbs shall have a minimum cube crushing strength of 25
N/mm2
at 28 days.
Local irregularities in ground level must be graded out prior to excavating for the fence post
foundations. This will ensure the fence is erected to a reasonable level, and does not follow
every minor deviation in ground level.

4.7 FENCE EARTHING
Where metal fences or posts are used, there is a requirement to provide suitable earthing for
the fence. At all sites with steel gates then each gate leaf must be bonded to it’s respective
gate post with a 70mm2
copper earth conductor. Additionally a 70mm2
buried copper earth
conductor must be provided to connect the two gate posts together to provide earth
continuity when the gates are open.
4.7.1 Primary/Grid sites
The preferred option is to have a 3 metre separation (or absolute minimum of 2 metres)
between the fencing and any other metal item connected to the main substation earth grid.
The fencing can then be separately earthed and NOT connected to the main substation
earth. Steel support columns (& associated cables) for lighting or security cameras must not
be erected within this 2m clearance zone. Insulated support columns are permitted within this
zone. If the fence is separately earthed then any metallic pipes or cables which run under the
fence shall be insulated (e.g. ducted) in the ground for 2m either side of the fence. It is
essential that precautions are in place to ensure that third party fences are not connected to
the metal substation fence. Electric security fences shall be designed not to compromise the
integrity of any segregated fence or insulted fence sections.
If plant has been positioned within 2m of the substation fence (giving rise to possible touch
voltage hazards), there are several options available to eliminate this hazard, these options
should be considered in the following order:-
a) Moving the fence or equipment to increase the separation or replace the section of
fence with a non-metallic barrier (e.g. brick or concrete panel). This will maintain the
preferred standard earthing design option.
b) Bond the fence in the immediate vicinity of the substation plant in question to the
earth grid. Install insulated fence sections either side of this bonded fence to isolate it
from the main fence. These insulated fence sections will be mounted on insulated
bushes at fence support post. A perimeter electrode must also be installed 1m
outside the bonded section of fence, buried 0.6m deep and bonded to the earth grid.
Where only a limited section of fence is affected, it is permitted to install up to a
maximum of two adjoining insulated fence sections. This creates an isolated fence
section which will be earth free.
c) Bond the fence to the substation earth grid and install a perimeter electrode around
the entire site which is bonded to the earth grid. This is the combined earth grid/fence
design. If the substation is classified as hot it will be necessary to consider how this
arrangement would affect the hot zone.
d) Installing an insulated barrier between the plant and fence.

4.7.2 11kV Distribution sites
At cold 11kV distribution substations where the 2 metre minimum spacing cannot be
achieved, then the fencing must be bonded to the substation earth at two separate points
using 70mm2
earth conductor. In addition a perimeter electrode shall be installed 1m outside
the fence (and 0.6m deep). If this is not possible a perimeter electrode bonded to the fence
and main earth grid shall be installed 0.6m directly below the fence where this can also form
part of the plant perimeter electrode.
At ‘HOT’ distribution sites, an earthing assessment must be carried out before the steel
fencing option is agreed. At some hot distribution sites it may be necessary to use other
types of fences or walls to avoid problems with the earthing system.
If the entire fence is greater than 2m from any item of plant then the fence shall not be
bonded to the HV earth electrode. In this case any earth wires passing under the fence shall
be insulated 2m either side of the crossing.

Fencing Specification for Substations

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