S-GEN-EARTH-00.pdf

0 JAN 2022 First Issue
Rev. Date Description/issued for
Client: ADDC/ AADC
STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRICITY DISTRIBUTION WORKS
Title: EARTHING/GROUNDING SYSTEMS
DOCUMENT NO: S-GEN-EARTH-00.DOCX Rev: 0-2022 Sheet: 1 of: 24
STANDARD TECHNICAL SPECIFICATIONS FOR ELECTRIC WORKS
Earthing/Lightning
Earthing/Grounding Systems
Group: General specifications
Subject: Earthing Grounding System

Client: ADDC/ AADC
Title:
EARTHING/GROUNDING SYSTEMS
INDEX
1 SCOPE.............................................................................................................................. 4
2 APPLICATION FIELD.................................................................................................. 4
3 REFERENCE DOCUMENTS ....................................................................................... 4
3.1 ADDC/AADC specifications ............................................................................................ 5
3.2 Reference standards........................................................................................................... 5
3.3 Regulation and law............................................................................................................ 5
4 SERVICE CONDITIONS .............................................................................................. 5
5 TECHNICAL FEATURES AND RATINGS................................................................ 6
5.1 General .............................................................................................................................. 6
5.2 Grounding/earthing for safety ........................................................................................... 6
5.2.1 Protection of circuits and equipment................................................................................. 7
5.2.2 Protection of personnel...................................................................................................... 7
5.3 Grounding/earthing for lightning protection ..................................................................... 8
5.4 Grounding/earthing for electronics and telecommunication ............................................. 8
6 SIZING OF THE MAIN DISPERSION GRID ............................................................ 8
6.1 General .............................................................................................................................. 8
6.2 Sizing of the main dispersion grid................................................................................... 10
6.2.1 Soil and the ambient........................................................................................................ 10
6.2.2 Main dispersion grid........................................................................................................ 11
6.2.3 The step, touch and transfer voltages .............................................................................. 11
6.3 Equipment and material requirements............................................................................. 12
6.3.1 Conductors ...................................................................................................................... 12
6.3.2 Rods................................................................................................................................. 15
6.3.3 Connections..................................................................................................................... 15
6.3.4 Miscellaneous.................................................................................................................. 15
6.3.5 Low Resistance Shield Conductors................................................................................. 16
6.4 Earthing /Grounding Applications .................................................................................. 16
6.4.1 Overhead Line Tower...................................................................................................... 16
6.4.2 Power Transformer and Reactor...................................................................................... 16
6.4.3 MV Power Cables ........................................................................................................... 16
6.4.4 GIS .................................................................................................................................. 17
6.4.5 Fixed earthing/grounding switches.................................................................................. 17
6.4.6 Lightning arrestors .......................................................................................................... 17
6.4.7 Overhead lines wooden poles.......................................................................................... 17
6.4.8 Light poles....................................................................................................................... 17
6.4.9 Panels and cubicles.......................................................................................................... 17
6.4.10 AC and DC distribution equipment................................................................................. 17
6.4.11 Steel Structure ................................................................................................................. 18
6.4.12 Operating Handles and Switch Shafts............................................................................. 18
6.4.13 Fences and Service Areas outside of Fences................................................................... 18
6.4.14 Earth pits in basements level........................................................................................... 18

Client: ADDC/ AADC
7 TESTING AND INSPECTION.................................................................................... 19
7.1 General ............................................................................................................................ 19
7.2 Factory tests..................................................................................................................... 19
7.2.1 Type tests......................................................................................................................... 19
7.2.2 Sample tests..................................................................................................................... 20
7.2.3 Routine tests .................................................................................................................... 20
7.3 Site tests........................................................................................................................... 20
8 QUALITY AND CERTIFICATION........................................................................... 21
8.1 Documentation supplied during the tender...................................................................... 21
8.2 Document to be supplied after the order ......................................................................... 21
9 DELIVERY, HANDLING AND LOGISTIC ISSUES............................................... 21
10 EXCEPTIONS............................................................................................................... 21
ANNEX A - STEP VOLTAGE MEASUREMENT CIRCUIT CONFIGURATION................ 22
ANNEX B - TOUCH VOLTAGE MEASUREMENT CIRCUIT
CONFIGURATION...................................................................................................... 23
ANNEX C – REFERENCE DESIGN............................................................................................ 24

Client: ADDC/ AADC
1 SCOPE
The scope of this specification is to provide the technical requirements for the design,
manufacturing, inspection, factory tests, packing, shipping, delivery to site of conductors and all
accessories for the earthing/grounding systems of LV, MV Substations and any combination of
them.
2 APPLICATION FIELD
This specification refers to the earthing/grounding systems of the substations in the distribution
network of ADDC/ AADC companies.
This document specifies the features and tests that must be accomplished in the design of
substation earthing grid.
3 REFERENCE DOCUMENTS
The list of the reference documents is indicated in the following paragraphs.
In case of discrepancy between these specifications and any of the applicable Codes and Standards,
the following order of precedence shall apply:
1) ADDC/AADC specifications
2) applicable reference standards
3) other documents.
The Supplier shall note that compliance with the provision of these specifications does not relieve
him from his responsibility to supply the equipment and accessories of proper design, electrically
and mechanically suited to meet the operating guarantees at the specified service conditions.

Client: ADDC/ AADC
3.1 ADDC/AADC specifications
The following internal specifications are provided in table 1.
Table 1 List of ADDC/AADC specifications
S-GEN-SER S-GEN-COR
S-GEN-NET S-CIV-SOIL
S-GEN-ID
3.2 Reference standards
The last edition of the standards mentioned in Table 2 that shall be take in consideration.
Table 2 List of standards
Standard Description
IEEE Std 80 Guide for safety in AC substation earthing
IEEE Std 81 Guide for Measuring Earth Resistivity, Ground Impedance, and Earth Surface Potentials of
a Grounding System
IEEE Std 1048 Guide for Protective Grounding of Power Lines
IEEE Std 1100 Recommended Practice for Powering and Grounding Electronic Equipment
IEC 60228 Conductors of insulated cables
ANSI/UL 467 Grounding and Bonding Equipment
ASTM B48 Standard Specification for Soft Rectangular and Square Bare Wire for Electrical conductors
ASTM B910 /
B910M - 07
Standard Specification for Annealed Copper-Clad Steel Wire
3.3 Regulation and law
All works shall be in accordance with the following Regulation and laws:
• Regulation and Supervision Bureau Water, Wastewater and Electricity Sector Emirate of Abu Dhabi
Emirate – The Electricity Wiring Regulations – revision 2014
The prescription included in the Regulations and Law shall prevail on all other international
standards mentioned in paragraph 3.2.
4 SERVICE CONDITIONS
The service conditions are specified in S-GEN-SER, in case something is not or not properly
specified regarding the service conditions, the Reference Standards prescriptions shall be
considered.

Client: ADDC/ AADC
5 TECHNICAL FEATURES AND RATINGS
5.1 General
This specification covers the technical requirements for Earthing/Grounding Systems in
substations and/or switchyards, to protect people, equipment, to allow safe operation and
maintenance of the electrical installations and ensure a stable network.
The Earthing/Grounding System, even when designed with a very low resistance, cannot be
considered as an equal-voltage surface. Substantial system voltage differences may occur and may
directly influence through a number of factors such as system resistance, system geometry and
distribution of ground currents, ground resistivity, and frequency of the transient.
The Earthing/Grounding System shall include earthing grid, raisers, grounding rods and all
required earthing/grounding connections.
Earthing/Grounding Systems shall perform satisfactorily and reliable for the whole lifetime (50
years) of the substation and/or switching yard without deterioration due to corrosion. It should
continually maintain a low resistance to the ground, satisfy thermal stability, and be capable of
carrying maximum anticipated full fault currents without deterioration.
The Supplier shall carry out ground resistivity and aggressiveness of soil measurements of the
whole Substation plot. If a plot will be filled with a soil layer greater than 1 m to raise the level,
soil resistivity measurements–shall be done after the filling. Based on the results of these
measurements and taking into account the system parameters, the calculations and design shall be
carried out. The calculation shall indicate areas where impermissible touch and step voltage exists,
studying the convenient recovering measures to mitigate the highest voltages values, recovering
the necessary safety in all the considered areas. This shall include any place within the substation
premises and the area surrounding around the substation and/or switchyard boundary/fence
(approximately 3 m outside the boundary), where people/vehicles are likely to pass by.
Three types of grounding/earthing shall be considered:
• Connection to ground of the equipment and metallic part either for safety of personnel, equipment and
facilities,
• Connection to ground for lightning protection,
• Connection to ground for equipotential reason of electronics, calculators and telecommunication
devices.
5.2 Grounding/earthing for safety
When the safety of people, equipment and facilities against electrical hazards is considered, it is
necessary to take into account both the earthing and the overcurrent protection.
Personnel shall be protected from a direct electrocution, equipment and circuits shall be protected
against failure of insulation.

Client: ADDC/ AADC
Grounding and bonding practices are important when done properly and will protect personnel
from electrical shock hazards and ensure safe electrical system operation. Some indications to
obtain these results are:
• Keeps equipment enclosures and other normal metal parts safe to touch.
• Limits unintended voltage on the electrical system imposed by lightning, surges or unintended contacts.
• Bonds electrical equipment together to establish a low impedance path from the fault location to supply
source, facilitating the protective devices operation.
• Establishes a stable voltage to ground during operation, including short circuits.
• Keeps electromagnetic influences avoiding wrong operations.
• Prevent objectionable current.
5.2.1 Protection of circuits and equipment
Equipment and circuits are protected by circuit breakers, fuses or protective relays. Their
intervention is proportional to the current value and the time of intervention is selected in
accordance with the characteristics of the protected system. The values of the currents are defined
by the source, the impedance of the circuit up to the faulted point and the path back to the source.
Should the returning path be through a metallic conductor, this shall be correctly sized taking into
account the maximum current value and the maximum temperature accepted for the conductor
itself.
Should, on the other hand, the returning path including the soil, it will be necessary to size a
connection, usually a grid or some rods, between the system and the soil to assure the minimum
impedance of the path.
The grounded conductors shall route with ungrounded ones and shall connect to the grounding
grid all metallic parts and equipment
The sizing of this grid, group of rods or any combination of them can be done following the rules
given by the internationally accepted standards approved also by TAQA/ADDC/AADC.
5.2.2 Protection of personnel
The protection of personnel is connected to the maximum current flowing into the personnel
bodies. The human body have a resistance and when it is connected between two conductors at
different voltages a current will flow through it.
The human body react differently if crossed by AC or DC current. Different levels of current can
be identified to each of these sources:
• Perception level 0.5 mA AC2 mA DC
• Tolerable permanent level 10 mA AC200 mA DC
• Tolerable limit for 10 ms 200 mA AC300 mA DC
• Fibrillation level (200 ms) 500 mA AC500 mA DC
• Fibrillation level (500 ms) 75 mA AC400 mA DC
Taking into account a minimum internal resistance of the human body of approximately 1000 ,
the international safety standards require the safety permanent and transient level of voltage for
either the contact or step.
As mentioned above, an underground grid, including eventually a set of rods is used to assure the
maximum tolerable voltage values. The sizing of the grid shall obey to standard rules and shall be
approved by TAQA/ADDC/AADC.

Client: ADDC/ AADC
5.3 Grounding/earthing for lightning protection
The damage caused by lightning can be very significant. Lightning is of high energy. The lightning
stroke has a very fast rise in current and much of what applies to high frequencies also applies to
lightning due to the fast rise of the front of wave.
The connection to ground shall done in a very short and direct form, through conductors isolated
from the equipment. The conductors connecting the lightning attractor system to ground shall run
in a form which exclude as far as possible the contact of personnel. The conductors shall be
connected to rods driven directly in the soil at a deep greater than the dispersion grid.
The rods shall be connected to the dispersion grid in order to control the potential differences
between the equipment and to maintain the step and contact voltages at a tolerable value.
5.4 Grounding/earthing for electronics and telecommunication
The coordination between electrical and telecommunication bonding and grounding systems is
essential during design and installation. Essentially all the zero-reference points of the electronics
and telecommunication equipment shall be connected forming a network independent and isolated
from the earthing of the power equipment. This “zero grid” shall constitute the earthing of the
electronics and telecommunication system and a common reference for all these instruments.
The “zero grid” shall be connected to the main dispersion power grid in only one point, allowing
the dispersion to soil of possible unwanted little currents, but avoiding the unwanted possible
overvoltage during the transient phenomena of the power system.
6 SIZING OF THE MAIN DISPERSION GRID
6.1 General
The function of an Earthing/Grounding System for an electrical installation shall be threefold:
• To maintain the potential of any part of the installation at a definite value with respect to the ground.
• To allow current to flow in the event of a fault to ground, so that the protective equipment will operate,
and the faulty circuit thus become isolated.
• To ensure that in the event of a fault, equipment normally ‘dead’ (unenergized) does not attain a
dangerous potential above or below ground.
The earthing grid design and testing process in resumed in Figure 1.
As general indication, meshed earthing gird shall be designed for primary substation while for
indoor/outdoor distribution substation or packed units the earthing grid shall be realized by means
of rods interconnected with wires.
Annex D is reporting reference case studies to be considered as design guidelines for the purpose
of earthing grid design.

Client: ADDC/ AADC
Figure 1 - Earthing grid design and earthing process
CALCULATION OF:
- Touch voltage (Vtouch)
- Step voltage (Vstep)
SOIL INVESTIGATION RESULTS
CREATION OF MULTILAYER
EARTH-MODEL
EARTHING GRID DESIGN
CALCULATION OF MAX VOLTAGE:
- Touch voltage (Vmax_touch)
- Step voltage (Vmax_step)
NETWORK PARAMETER:
- Max. earth fault current
- Max. earth fault clearing time
Vtouch> Vmax_touch
Vstep> Vmax_step
CONSTRUCTION
SITE MEASUREMENT:
- Touch voltage (Vmt)
- Step voltage (Vms)
Vmt > Vmax_touch
Vms > Vmax_step
REDESIGN
EARTHING GRID COMPLETED
YES
NO
NO
YES

Client: ADDC/ AADC
6.2 Sizing of the main dispersion grid
6.2.1 Soil and the ambient
The sizing of the grid shall start with the measurement of:
• Soil resistivity
• Aggressiveness of the soil (such as redox potential, moisture content, pH value, presence of dissolved
salts/organic acids, etc.)
The measurements shall be performed to obtain a multilayer model of the soil with minimum of
two layers but including a third one if the lower layer is not assuring a satisfactory resistivity value,
which can assure a good and safe performance of the grid. Soil investigation methods are described
in technical specification S-CIV-SOIL.
For the determination of the resistivity of the soil it shall be taken into account the variation of the
humidity and the temperature during the years, to assure that the performance of the grid shall not
drop under a defined minimum value during the lifetime of the plant.
For the effect of corrosion, an allowance, which should not be less than 10% of the calculated
Earthing/Grounding grid size, shall be considered. The aggressiveness of both the soil and the
ambient in general shall be taken into account during the selection of the materials constituting the
grid itself as the conductors, the rods and the connectors.
Copper is essentially immune to corrosion, because of the naturally protective film that forms on
the metal’s surface. Possible corrosion, however, can be verified for elevated sulphate or chloride
concentrations. Soils containing either inorganic acids or appreciable amounts of ammonia
compounds can be unusually aggressive to copper. Very low soil resistivity may indicate a soil
that could be aggressive.
Proper counter-measures in case of aggressive soil, varies on case by case basis depending on the
specific project soil measures, specific site features and constrains. For this reason, it is possible
to include in the present specification only some general indication and practices. It is Supplier
responsibility to develop a detailed study to be submitted to TAQA/ADDD/AADC for approval.
Some indications can be taken into consideration, as improving drainage, avoiding
nonhomogeneous and cinder backfills and using of selective nonaggressive backfills. In extreme
cases, the conductors can be encased in concrete blocks. The calculation of the performance of this
particular solution may be quite complex and shall be carefully studied taking into account the
chemical and conductive characteristics of the used concrete.
For the conductors exposed to the air, in case of strong, aggressive industrial pollution, may be
possible the use of other metals, as hot dip galvanized steel or stainless steel.

Client: ADDC/ AADC
6.2.2 Main dispersion grid
The conductor to be used for the grid shall be sized to carry the full current in the worst case of
short circuit occurring in the substation, allowing the return path to the source in safe and reliable
form.
It is recommended that all the armature of the building shall be connected to the dispersion grid.
This has as a consequence the increase of the performance of the system, due to the participation
of the electrodes encased in the concrete.
The performance of the dispersion grid shall be designed using the multilayer model of soil and
with a procedure mentioned in the Reference Standard (see paragraph 3.2). Computer programs
based on those recommendations shall be used with the prescription that the same are based on the
multilayer model of the soil and/or on the finite element methodology.
It is recommended that grounding resistance of the grounding system against the ground be of less
than 1 ohm for primary substations and up to 10 ohm for distribution substations and up to 30 ohm
for line towers; lower values shall be highly recommended, while higher values because of some
areas soil resistivity must be approved by ADDC/AADC/TAQA according to Applicable
Standards.
This value shall be verified by measures and test. Should the value not reached, some additional
rod shall be installed up to reach the correct value.
6.2.3 The step, touch and transfer voltages
The design of the earthing grid shall have the final goal to obtain step and touch voltages lower
that the maximum allowed values according to IEEE 80 Standard.
Maximum step voltage
Maximum touch voltage
Where:
• Cs is is the surface layer derating factor
• ρs is the surface material resistivity in Ω·m
• ts is the duration of shock current
Step and touch voltages calculations have to be performed according to the reference standard
IEEE 80 or using dedicated software with finite element calculation method. The software shall
be approved by TAQA/ADDC/AADC.
Calculation of possibly transferred voltages induced in the metallic parts shall be performed, with
particular reference to fences, pipes, neutral conductors and other metallic elements installed in
the substation that may constitute dangerous points in case of faults or lightning strokes.
The prescription of Standard IEEE 80 shall be followed with special attention to low voltage
neutral wires. According to IEEE 80, if the LV neutral is distributed outside the substation and
ground potential rise (GPR) is higher than safety levels, it is recommended to earth separately the
LV neutral from substation earthing grid and isolate it at least to withstand GPR.

Client: ADDC/ AADC
6.3 Equipment and material requirements
6.3.1 Conductors
The conductors shall be sized to have the capacity to transport all the short circuit current from the
fault point to the source, if connected to the same grid. The sizing shall assure an allowance to take
into account possible increasing in the short circuit capacity. The material used is preferred to be
copper clad steel according to Standard ASTM B910 / B910M - 07. Copper or galvanized- or
stainless steel, should the aggressiveness of the ambient suggest this choice may be proposed as
alternative (with a proper motivation) to be submitted to TAQA/ADDC/AADC for approval.
It is a matter to consider that the underground part of the grid shall maintain a maximum
temperature below the 200°C during the flow of the current due to the fault. This can assure the
maintenance of the critical level of the humidity in the soil even after an operation of the grid with
the consequent overtemperature.
The conductors used for the zero-reference system in the electronics and telecommunication
equipment shall be insulated cables, connected to dedicated common bars in each room, cast into
the surface concrete of all building floors. The location of the bars dedicated to the potential
equalizing system shall be submitted to TAQA/ADDC/AADC for approval.
The minimum cross sections of conductors, based on copper conductivity, are reported in the data
sheet D-GEN-EARTH
It is suggested, taking into account the reliability of the connections, to install always at least two
conductors for the grounding of the panels/main equipment.
6.3.1.1 Construction and rating
Copper Clad Steel Wires minimum technical requirements for design, engineering,
manufacture, inspection, testing and performance shall be aligned with ASTM B910/B910M-
Standard
The cross section shall be defined by a calculation which shall take in to account the actual short
circuit current for the specific project.
The copper-clad steel grounding conductor and copper-clad steel ground rods shall be of
manufacturer's standard design and shall meet or exceed the requirements of this Specification in
all respects.
The copper-clad steel grounding conductor shall be made from bare round annealed copper-clad
steel wires conforming to ASTM B910/B910M. Below Table 2 is showing a set of typical
conductors normally used for the application.

Client: ADDC/ AADC
Table 3
Conductor Size Designation Nominal Diameter Nominal Total
Cross-Section
Minimum Rated
Tensile Strength
Max. DC
Resistance at 20°C
AWG Overall Single wire
mm mm mm2
N/mm2
Ohm/km
7 No. 10 7.77 2.558 36.83 9.15 1.244
7 No. 9 8.71 2.906 46.44 11.5 0.9865
7 No. 8 9.78 3.264 58.57 14.54 0.782
7 No. 7 11.00 3.665 74.87 18.34 0.6202
7 No. 6 12.34 4.115 93.1 23.13 0.492
7 No. 5 13.87 4.62 117.42 29.14 0.3903
7 No. 4 15.57 5.189 148.04 36.77 0.3094
19 No. 8 16.31 3.264 158.97 39.45 0.2892
19 No. 7 18.31 3.665 200.45 49.79 0.2294
19 No. 6 20.57 4.115 252.71 62.77 0.1819
19 No. 5 23.11 4.62 318.71 79.1 0.1443
Notes:
• The maximum DC Resistance at 20°C value is based on minimum individual wire diameter and
minimum conductivity of 39.21 % corresponding to a resistivity of 0.0440 ohm mm2
/m.
• The tensile load is taken as ninety percent (90%) of the sum of the tensile loads of the individual
wires and is based on minimum tensile strength of 276 N/mm2
as referred in ASTM B910/B910M.
During the single project design phase it is strongly suggested to round up the conductor’s cross
sections in few standardized groups, avoiding possible errors in their installation.
6.3.1.2 Materials
The copper-clad wire shall consist of a core of homogeneous open-hearth, electric-furnace, or
basic-oxygen steel with a continuous outer cladding of copper thoroughly bonded to the core
throughout. The copper-clad wire shall be free from copper discontinuities and all imperfections
not consistent with good commercial practice. The nominal conductivity of copper-clad steel Wire
shall be 40% IACS (International Annealed Copper Standard). The electrical resistivity of
copper-clad steel wire at a temperature of 20°C shall not exceed 0.0440 ohm mm2
/m. All wires
in the grounding conductor shall be of the same grade and quality.
6.3.1.3 Fabrication
The copper-clad steel grounding conductors shall be constructed in conventional concentric-lay-
stranded type. The copper-clad steel grounding conductors shall have left-hand lay and the
preferred lay is 13.5 times the diameter of that layer, but the pitch of the strand shall be neither
less than 10 nor more than 16 times this diameter. All copper-clad steel wires in the conductor
shall lie naturally in their true positions in the completed conductor. They shall remain in position
when the conductor is cut at any point and shall permit re-stranding by hand after being forcibly
unravelled at the end of the conductor. Joints or splices may be made in the finished individual
copper-clad steel wires composing concentric- lay-stranded conductor but these splices shall not
decrease the strength of the finished conductor below the minimum breaking strength specified in
Table 01. These joints or splices shall not be closer than 15 meters to any other joint in the same
layer in the conductor. The type of joints or splices in individual copper-clad steel wires shall be
of weld-annealed joints made by electric butt welding.

Client: ADDC/ AADC
6.3.1.4 Tolerances
The actual diameter of the copper-clad steel wires forming the conductor shall not vary from the
specified diameter by more than ± 1.5% expressed to the nearest 0.003 mm. The cross-sectional
area of the completed conductor shall not be less than 98% of the area specified. The cross-
sectional area of a conductor shall be considered to be the sum of the cross-sectional areas of its
component wires at any section when measured perpendicularly to their individual axis.
The minimum copper thickness due to eccentricity shall not be less than 5% of the individual wire
diameter (10% of the wire radius).
6.3.1.5 Reel Design
Reel shall be of non- returnable wood. The length of copper-clad steel grounding conductor per
reel shall be 2000 meters with a permissible variation of ±5%, unless otherwise different lengths
are required as per actual site requirements or as agreed between ADWEA/ADDC/AADC and the
manufacturer.
6.3.1.6 Markings
Each end of the copper-clad steel grounding conductor in the reel shall bear a non-corroding tag
identifying the following:
• Grade of grounding conductor
• Diameter/Size of grounding conductor
• Average Breaking Strength
• Length of grounding conductor (on the one end only)
• Stranding
Each reel shall be stencilled to show all information as specified above plus additional information
as follows:
• Manufacturer's Name and Country of Origin
• Year of Manufacture
• Serial Number
• Size of Reel
• Gross Weight
• TAQA/ADDC/AADC Purchase Order Number/Contract Number.
• Consignee Address
• Direction of Rolling
All markings shall appear on both sides of the reel.

Client: ADDC/ AADC
6.3.2 Rods
The rods shall be copper-clad steel, as usual choice, but may be also galvanized or stainless steel
if the aggressiveness of the soil should indicate this opportunity. The choice of material shall be
submitted to the approval of TAQA/ADDC/AADC.
The length of the rods shall be selected taking into account the thickness of the soil layers. The
rods shall reach the most favourable layer underground, normally rods length varies between 3 and
5 meters.
The rods shall be installed with a spacing of two times their length, as a minimum, avoiding any
possible interference of one another.
6.3.3 Connections
All medium-voltage and low voltage permanent equipment shall be connected to the
grounding/earthing grid with two conductors each sized for the full fault current.
Overhead transmission line ground wires and substation earthing/grounding systems shall be
electrically connected.
Each metallic device within the substation boundary must be equipped with an earthing/grounding
bolt/screw of sufficient diameter to connect the earthing/grounding system.
All metallic construction parts and auxiliaries, especially gantries, auxiliary structures, supports,
apparatus, fences (all posts), control/protection cubicles shall be connected to the main dispersion
grid. The gates of the fence shall be earthed, and a gateway area potential control has to be
considered.
The earthing/grounding system of buildings shall be connected to the earthing/grounding system
of the substation. If an existing earthing/grounding system is ending at the front of a substation
building, the earthing/grounding network shall be extended.
The connections of all conductors constituting the main dispersion grid shall be done with
exothermic process. The compression connectors may be acceptable if the compression is taken
up to the fusion of the conductors and connector in a common body.
Bolted connections might be used only at locations inside the buildings.
Where necessary the Supplier shall foresee the necessary bi-metallic connections/accessories for
the connection among earthing grid elements and equipment.
6.3.4 Miscellaneous
Terminal lugs shall be of one hole, socket type, rounded edge lug, cast of high strength corrosion
resistance copper alloy. Machine screws, nuts, and washers used with the lugs shall be of bronze.
All flexible copper braids shall be made of flat, extra-flexible copper braid. Both ends shall be
encased in a seamless copper ferrule drilled in accordance with NEMA Standard or equivalent.
Ferrules shall be formed under high pressure ensuring dependable contact.

Client: ADDC/ AADC
6.3.5 Low Resistance Shield Conductors
Since it is impractical to completely eliminate system voltage differences, their effect must be
neutralized. Neutralization shall be accomplished by a low resistance shield conductor parallel to,
and in proximity of, the affected control circuit. Such a conductor may be the shielded control
cable, unused conductors of an unshielded control cable, or a separate shield conductor.
In trench systems, shield conductors, connected to the substation Earthing/Grounding System,
shall be attached to the sides tops of the trench. This results in placing the shield conductors
between the transient source and the control cables. These shield conductors should have
sufficient conductivity to carry fault currents without damage.
6.4 Earthing /Grounding Applications
6.4.1 Overhead Line Tower
The connection of ground conductor/electrodes to the Stub-angle shall be made with compression
lugs, fixed to the Stub-angles by 2 bolts of the size M16.
All contact surfaces on the tower stubs, connectors, rods, strips, wire leads etc. shall be thoroughly
cleaned prior to assembly. Finished connections shall be protected with a liberal coating of an
appropriate compound. Great care shall be taken for protecting the earthing/grounding against
corrosion from aggressive soil.
All wire leads shall be properly fixed to the connectors and all bolts shall be firmly tightened to
ensure that a good electrical connection is achieved.
All wires and strips shall be handled and installed in the best possible manner, free of kinks and
damage of any kind. Backfill for strip trenches shall be sieved material and thoroughly compacted
in layers.
After installation of the earthing/grounding system, Supplier shall measure the earth resistance at
each tower structure, submitting the results to TAQA/ADDC/AADC, for approval. The stringing
of the earth wire may commence only after final approval of the resistance values by
TAQA/ADDC/AADC.
OHL earth wire shall be connect to earth at both line end inside the substations. Moreover, each
tower shall be grounded at the earthing grid at tower base and through the earth wire. With this
configuration, in case of earth fault on a tower, the earth wire shall drain a portion of the earth fault
current far from the tower.
6.4.2 Power Transformer and Reactor
The transformer and shunt reactor tank shall be connected to the earthing/grounding system
following the same principles as for steel structures.
Directly grounded power transformer/reactor neutrals shall be connected by two copper
conductors (isolated from the transformer tank) to the main dispersion grid. The copper conductors
shall be properly clamped to a supporting steel structure.
6.4.3 MV Power Cables
Three core MV cable shall have sheath earthed at both sides.
Single core MV cable shall normally have sheath earthed at one side only.

Client: ADDC/ AADC
6.4.4 GIS
GIS earthing/grounding shall meet the requirements specified in IEEE Std 80-2000.
For high-frequency earthing, CIGRE (Group 23.10, Publ. Earthing of GIS – An application Guide)
shall be considered.
The GIS manufacturer shall evaluate:
• Induced enclosure currents
• Metal to metal touch voltage during internal and external GIS faults
• Justify that specified touch voltage criteria are met and submission of special precautions for
TAQA/ADDC/AADC’s approval.
6.4.5 Fixed earthing/grounding switches
Connections between any type of earthing/grounding device, as earthing/grounding switch, and
risers from the main dispersion grid shall be arranged through two insulated copper conductors
yellow-green. These conductors shall be properly clamped to the steel structure.
Each conductor shall be sized to have the capacity of carry the full earth fault current.
6.4.6 Lightning arrestors
Lightning arrestor grounding terminal shall be connected by two copper conductors to a dedicated
rod and the main dispersion grid. Arrester ground connections shall meet requirements as
specified in IEEE Std 80-2000. The copper conductors shall be properly clamped to the lightning
arrester supporting steel structure.
In case of pole mounted surge arresters, surge arresters shall have an individual earthing through
green-yellow insulated cables connecting the surge arrester earth terminal with the earthing grid
at pole’s base.
6.4.7 Overhead lines wooden poles
Steel work in wood poles shall be earthed at all section "H" poles and other "H" poles which are
fitted with transformers, switchgear, cable boxes or other apparatus. At such "H" poles all steel
work shall be bonded and earthed. Earthing and bonding wire should be stapled to poles at
intervals smaller than 30 cm.
6.4.8 Light poles
Poles for lighting within the substation area shall be connected to the main dispersion grid with
copper cables. The connection shall be individual for each pole.
6.4.9 Panels and cubicles
Control and protection panels, marshalling cubicles and transformer control panels shall be
connected to the earthing/grounding system with two conductors, irrespective of whether the
cubicles are mounted: on an earthed steel structure or not.
6.4.10 AC and DC distribution equipment
AC distribution equipment, battery chargers and DC distribution panels shall be connected to the
earthing/grounding system with two conductors, irrespective of whether the equipment is
mounted: on an earthed steel structure or not.

Client: ADDC/ AADC
6.4.11 Steel Structure
Each steel structure that carries electrical apparatuses shall be connected to the earthing/grounding
system. To ensure a contact even if a connection fails or a cable is cut off, each structure must be
connected via two different risers to two different locations of the dispersion grid.
Steel structures underneath conductors shall be properly connected to the grounding grid to sustain
the full fault current.
Steel structures constructed as one unit, with all parts welded in a common body, can be utilized
for grounding of electrical parts installed on it, if the steel structures are earthed as follows:
• For gantries, earthing/grounding system shall be connected at two points.
• Sufficient conductive cross-sections of the gantry supporting structure.
• Electrically conductive connections at the gantry structure shall be bolted or welded.
6.4.12 Operating Handles and Switch Shafts
Operating handles and Switch Shaft groundings shall meet requirements as specified in IEEE Std
80-2000.
6.4.13 Fences and Service Areas outside of Fences
Fences and Service Areas outside of Fences groundings shall meet requirements as specified in
IEEE Std 80-2000.
6.4.14 Earth pits in basements level
Earth pits at the basement of the high-rise building shall be acceptable subject to approval of
TAQA/ADDC/AADC.

Client: ADDC/ AADC
7 TESTING AND INSPECTION
7.1 General
All earthing/grounding elements/devices shall be tested in the manufacturer’s work as far as
applicable. The Supplier may be required to carry out any one or all of the tests stated in this
specification under witness of TAQA/ADDC/AADC or his representatives.
Testing of the earthing/grounding systems shall be performed in line with this specification and
in accordance with the relevant IEC Standards and other Standards as may be approved by
TAQA/ADDC/AADC.
Acceptance by TAQA/ADDC/AADC’s representative of any equipment shall not relieve the
manufacturer from any of his performance guarantees or from any other obligations.
TAQA/ADDC/AADC reserves the right to perform checks during manufacturing process at any
time or all the times.
It shall be at the discretion of TAQA/ADDC/AADC to witness tests on 100%, or any percentage
quantity of each lot for routine tests, apart from the type tests, wherever called for.
Tests of earthing/grounding systems shall comprise factory and site tests.
7.2 Factory tests
7.2.1 Type tests
Cables, hardware and materials shall be subjected to the type tests in accordance with the
applicable IEC, ANSI Standards and/or IEEE recommendation.
Evidence shall be given that the proposed earthing/grounding systems under this specification
have been subject to all type tests at an internationally recognized testing station, like KEMA or
equivalent. If deemed necessary, TAQA/ADDC/AADC will decide whether additional tests are
necessary to be performed by the Supplier.
An internationally recognized laboratory shall certify the type test reports.
The Supplier shall submit certified copies of type test certificates covering the proposed
earthing/grounding components.
Type tests certificates/reports shall be considered acceptable if they are in compliance with the
relevant Standards and the following:
1. Type Tests conducted at an internationally recognized laboratory acceptable to
TAQA/ADDC/AADC.
2. Type Tests conducted at the Supplier’s laboratory and witnessed by representatives from an
internationally recognized third party acceptable to TAQA/ADDC/AADC.
If the presented type test reports are not in accordance with the above requirements,
TAQA/ADDC/AADC may decide to perform again the type tests in the Supplier’s premises or
other places subject to the approval of TAQA/ADDC/AADC and at no additional cost. These tests
shall be performed in the presence of an internationally recognized laboratory, which should issue
the relevant type test certificates upon successful test.

Client: ADDC/ AADC
7.2.2 Sample tests
The sample tests shall be performed in accordance with international and/or the Supplier standard
accepted by TAQA/ADDC/AADC.
Sample tests shall be performed, by selecting the samples from each lot of earthing/grounding
components/material. Sampling shall be as per the international standards.
The tests shall comprise as a minimum the following tests:
• Visual checks and measurements of dimensions
• Earthing/grounding components labeling.
7.2.3 Routine tests
Earthing/grounding systems shall be subjected to routine tests as per the applicable IEC, ANSI
Standards and/or IEEE recommendation.
Routine test certificates shall be submitted for TAQA/ADDC/AADC’s review and approval
before shipment of the earthing/grounding components.
The visual inspection of the earthing/grounding systems, in order to ensure that all components
are mechanically assembled and fixed properly and that there are no imperfections, shall be
performed.
The tests on earthing/grounding cables and conductors shall include, but not limited to, the
following general inspection as per ASTM B910 / B910M - 07:
• Stranded conductor: electrical and physical test before stranding only (no repetition after stranding).
• Tensile strength tests
• Elongation tests
• Conductor resistivity tests
• Dimension measurement
• Surface finish inspection
• Weight of conductor
• General inspection
• Measurement of dimensions.
7.3 Site tests
The following site test shall be performed:
• Earthing resistance measurement: Fall-of-Potential Method or Potential Gradient Measurement
• Step voltage measurement: Footprint-Electrode Method according to IEEE Std 80 considering a 50 kg
person – see Annex A for test circuit configuration
• Touch voltage measurement – see Annex B for test circuit configuration

Client: ADDC/ AADC
8 QUALITY AND CERTIFICATION
8.1 Documentation supplied during the tender
The documentation supplied by the Supplier during tendering stage shall contain the following
minim elements:
• Data sheet D-GEN-EARTH filled in for tendering purpose
• Preliminary layout of the earthing grid
• Preliminary list of product and material and their associated technical material
• Method stamen for earthing grid calculation
8.2 Document to be supplied after the order
The documentation supplied by the Supplier after the order shall contain the following elements:
• Data sheet D-GEN-EARTH filled in for construction purpose
• Soil investigation report
• Earthing grid design calculation
• Detailed layout of the earthing grid, with connection details
• Final list of product and material with their associated technical documentation
• Method stamen for earthing grid laying and connection
9 DELIVERY, HANDLING AND LOGISTIC ISSUES
The Supplier is responsible for all the delivery procedures and provisions for storage of the
equipment in factory after the tests and until the transport operations.
The supplier shall pack the equipment with a suitable cases and protective measures granting the
safe delivery of the good at the final place of installation.
10 EXCEPTIONS
Possible exceptions to the present prescriptions, concerning the adoption of technical and/or
manufacturing aspects different from the ones prescribed in the present document, can be
evaluated by TAQA/ADDC/AADC.
In such a case, TAQA/ADDC/AADC will take into account the opportunity to require additional
tests with regard to the technical/manufacturing proposed solutions.
Such exceptions can be approved by TAQA/ADDC/AADC.

Client: ADDC/ AADC
ANNEX A - STEP VOLTAGE MEASUREMENT CIRCUIT CONFIGURATION

Client: ADDC/ AADC
ANNEX B - TOUCH VOLTAGE MEASUREMENT CIRCUIT CONFIGURATION

Client: ADDC/ AADC
ANNEX C – REFERENCE DESIGN
The following reference design and recommendation are annexed to the present specification as
guidelines.
• D.1 “ENGINEERING STANDARD – EARTHING CONTRACT No. D-101290”
• D.2 “EARTHING DESIGN REPORT - CONTRACT No. A-6466”
• D.3 “TECHNICAL RECOMMENDATION FOR EARTHING SYSTEMS - - CONTRACT No.
A-6466”
• D.4 “Executive summary EARTHING SYSTEM DESIGN: CUSTOMER PRIVATE AND
OUTDOOR 11/0.4 KV DISTRIBUTION SUBSTATIONS”

S-GEN-EARTH-00.pdf

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