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DUBAI WORLD CENTRAL INTERNATIONAL AIRPORTPHASE I – Design of BuildingsContract No. JXB1/BLD/431- PASSENGER TERMINAL BUILDING

SECTION 16060

GROUNDING AND BONDING

CONTENTS

PART 1 - GENERAL...............................................................................................................................................21.1 RELATED DOCUMENTS.......................................................................................................................21.2 SUMMARY...............................................................................................................................................21.3 SUBMITTALS..........................................................................................................................................21.4 QUALITY ASSURANCE.........................................................................................................................31.5 DEFINITIONS OF TERMS......................................................................................................................4

PART 2 - PRODUCTS AND SYSTEMS................................................................................................................52.1 STANDARD COMMERCIAL PRODUCTS............................................................................................52.2 SOIL SURVEY AND CALCULATIONS................................................................................................52.3 FAULT CURRENT AND DURATION...................................................................................................62.4 EARTH ELECTRODE SYSTEM DESIGN.............................................................................................62.5 GENERAL REQUIREMENTS.................................................................................................................82.6 GROUNDING CONDUCTORS.............................................................................................................102.7 CONNECTOR PRODUCTS AND EARTHING ACCESSORIES........................................................112.8 GROUNDING ELECTRODES...............................................................................................................12

PART 3 - EXECUTION........................................................................................................................................123.1 TRANSFORMER SUBSTATION EARTHING.....................................................................................123.2 EARTHING OF MAIN DISTRIBUTION BOARDS, PANELBOARDS, LIGHTING INSTALLATIONS AND WIRING ACCESSORIES.......................................................................................133.3 ELECTRICAL / MECHANICAL PLANT ROOMS AND FIXED MACHINERY..............................133.4 ROAD LIGHTING..................................................................................................................................143.5 SIGNAL AND COMMUNICATION SYSTEMS..................................................................................143.6 CLEAN EARTH GROUNDING.............................................................................................................143.7 EARTHING AND BONDING MULTICORE CABLES.......................................................................143.8 EARTHING OF FENCES........................................................................................................................153.9 INSTALLATION GENERAL.................................................................................................................163.10 CONNECTIONS................................................................................................................................173.11 FIELD QUALITY CONTROL...........................................................................................................173.12 GRADING AND PLANTING............................................................................................................18

GROUNDING AND BONDING Section 16060 - /18November 2006


PART 1 - GENERAL

1.1 RELATED DOCUMENTS

A. Drawings and general provisions of the Contract, including Conditions of Contract and Division 1 Specification Sections, apply to this Section.

B. The following Sections contain special requirements that relate to this Section:

1. Division 2 Section "Underground Ducts and Utility Structures" for ground earth pits.2. Division 13 Section "Lightning Protection" for additional grounding and bonding

materials.3. Division 16 Section "Basic Electrical Materials and Methods".4. Division 16 Section "LV Conductors and Cables".

1.2 SUMMARY

A. This Section includes complete installations to earth every source of energy and to provide protective earthing and equipotential bonding, based on the TN-S system arrangement, including:

1. 11kV Switchgear and Ring Main Unit (RMU).2. Transformer neutral earthing.3. Generator sets neutral point4. LV Switchgears.5. Main earthing terminals or bars in electrical and mechanical rooms.6. Exposed conductive parts of electrical equipment (light fittings, switches and socket

outlets, etc.).7. Extraneous conductive parts.8. Fences & gate earthing.9. Separate clean earth for the ELV systems for each ELV and control room (less than 1

ohm)

Earthing requirements specified in this Section may be supplemented by special requirements of systems described in other Sections.

1.3 SUBMITTALS

A. Product Data: Prior to ordering materials, submit data for approval including, but not limited to, manufacturer’s catalogs for each type of product indicated including the following:

1. Ground rods.2. Connecting clamps.3. Earthing conductors, protective conductors, and bonding conductors.4. Connectors and other accessories.5. Exothermic welding kits and tools.

B. Qualification Data: For firms and persons specified in "Quality Assurance" Article.



C. Field Test Reports: Submit certified, numbered, written test reports to include the following:

1. Test procedures used and test conditions.2. Test results that comply with requirements.3. Results of failed tests and corrective action taken to achieve test results that comply

with requirements.

D. Shop and Construction Drawings: Submit Drawings for approval including, but not limited to, the following:

1. Overall earthing schematic indicating cross sectional area of all earthing, protective and bonding conductors.

2. Overall earthing layout indicating earthing provisions at substations, generator rooms, switchgear, distribution panel boards etc., identifying fittings used, insulation, plates and marking, passage and routing of earthing conductors, conduit, sleeves, grooves, niches etc., giving sizes and dimensions of component parts, and exact location of earth pits, rods and details of installation and connections, and exact routing of buried earthing conductors with indication of cross-section, depth of laying and covering.

E. Records: Submit the following:

1. Scaled Drawings, As-built, showing actual layout and specification of all components of earthing system, in accordance with requirements of the Specification, Division 1.

2. Nature of soil and any special earth arrangements etc.3. Date and particulars of soil conditioning method and agents if used.

F. Samples: Submit samples of conductors, as requested.

G. Final earthing design calculations for approval, clearly indicating expected maximum earth fault levels and suitable conductor sizes, before implementation.

1.4 QUALITY ASSURANCE

A. Installer Qualifications: Engage an experienced installer. Submit qualifications for approval.

B. Standards: Carry out work in accordance with the following:

1. IEC 60364-1 and 60364-4-41: Electrical Installations in Buildings.2. BS 7671 Requirements for Electrical Installations (IEE Wiring Regulations 16 th

Edition).3. Comply with BS 6651 (Protection of Structures against Lightning) when

interconnecting with lightning protection system.4. ANSI/IEEE/std 80: IEEE Guide for Safety in AC Substation Grounding.5. ANSI/IEEE/Std 81: IEEE Guide for Measuring Earth Resistivity, Ground Impedance,

and Earth Surface Potential of a Grounding System.6. BS 7430: Code of Practice for Earthing.7. DIN VDE 0141: Earthing Systems for Power Installations with Rated Voltages above 1

kV.8. BS EN 13601 Copper and copper alloys. Copper rod, bar and wire for general electrical

purposes.9. BS 1433: Specification for copper for electrical purposes. Rod and bars.10. BS EN 1057: Copper and copper alloys. Seamless round tubes for water and gas in

sanitary and heating applications.



11. BS EN 12449: Copper and copper alloys. Seamless round tubes for general purposes.12. BS EN 12451: Copper and copper alloys. Seamless, round tubes for heat exchangers.13. BS 7668: Specification for weldable structural steels. Hot finished structural hollow

sections in weather resistant steels.14. BS 6360: Specification for conductors in insulated cables and cords.15. BS EN 10029: Specification for tolerances on dimensions, shape and mass for hot

rolled steel plates 3 mm thick or above.16. BS EN 10113-1: Hot-rolled products in weldable fine grain structural steels. Delivery

conditions for thermomechanical rolled steels.17. BS EN 10113-2:1: Hot-rolled products in weldable fine grain structural steels. Delivery

conditions for normalized/normalized rolled steels.18. BS EN 10113-3: Hot-rolled products in weldable fine grain structural steels. Delivery

conditions for thermomechanical rolled sheets. 19. BS EN 10155: structural steels with improved atmospheric corrosion resistance.

Technical delivery conditions.20. BS EN 10210-1: Hot finished structural hollow sections of non-alloy and fine grain

structural steels. Technical delivery requirements.21. BS EN 10137-1: Plates and wide flats made of high yield strength structural steels in

the quenched and tempered or precipitation hardened conditions. General delivery conditions.

22. BS EN 10137-2: Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened conditions. Delivery conditions for quenched and tempered steels.

23. BS EN 10137-3: Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened condition. Delivery conditions for precipitation hardened steels.

24. BS EN 10025: Hot rolled products of non-alloy structural steels. Technical delivery conditions.

25. BS 7655-1-5: Specification for insulating and sheathing materials for cables. Elastomeric insulating compounds. Flame retardant composites.

26. BS 7655-0: Specification for insulating and sheathing materials for cables. General introduction.

27. BS 6004: Electric cables. PVC insulated, non-armoured cables for voltages up to and including 450/750 V, for electric power, lighting and internal wiring.

28. ISO 630: Structural steels.29. IEC 60502-1: Extruded solid dielectric insulated power cables for rated voltages from

1 kV to 30 kV.30. ITU: Directives concerning the protection of telecommunications lines against harmful

effects from electricity lines.

C. Comply with BS 6651 when interconnecting with lightning protection system.

D. DEWA regulations

E. Products shall be sourced either directly from manufacturer or from the manufacturer’s authorized dealer/agent.

1.5 DEFINITIONS OF TERMS

A. The following terms used on the Drawings and in the Specifications are equivalent and may be used interchangeably: "earth" and "ground"; "earthing" and "grounding".

B. Earth: Conductive mass of the Earth whose electric potential at any point is conventionally taken as zero.



C. Earth Electrode: Conductor or group of conductors in initial contact with, and providing electrical connection to, Earth.

D. Exposed Conductive Part: Any part which can be readily touched and which is not a live part, but which may become live under fault conditions.

E. Extraneous Conductive Part: Any conductive part not forming part of the electrical installation such as structural metalwork of a building, metallic gas pipes, AC ducts, water pipes, heating tubes etc. and non-electrical apparatus electrically connected to them i.e. radiators, cooking ranges, metal sinks etc. and non-insulating floors and walls.

F. Protective Conductor: Conductor used for some measure of protection against electric shock and intended for connecting together any of the following parts:

1. Exposed conductive parts.2. Extraneous conductive parts.3. Earth electrode(s).4. Main earthing terminal or bar(s).5. Earthed point of the source(s).

G. Electrically Independent Earth Electrodes: Earth electrodes located at such distance from one another that maximum current likely to flow through one of them does not significantly affect the potential of the other(s).

H. Main Earthing Terminal or Bar: The terminal or bar provided for the connection of protective conductors, including equipotential bonding and functional earthing conductors, if any, to the means of earthing.

I. Equipotential Bonding: Electrical connection to put exposed and extraneous conductive parts at a substantially equal potential.

J. Earthing Conductor: Protective conductor connecting main earthing terminal or bar of an installation to earth electrode or to other means of earthing.

PART 2 - PRODUCTS AND SYSTEMS

2.1 STANDARD COMMERCIAL PRODUCTS

A. Refer to Division 1 Section 01600, paragraph 2.1

2.2 SOIL SURVEY AND CALCULATIONS

A. The Contractor shall carry out an earth resistivity survey on each site and report in writing to the Engineer in accordance with the approved program. The report shall detail the methods and instruments used and the results of the surveys. Based on the results the Contractor shall include in the report his proposals for the resistivities to be used in the design of the earthing system.

B. The value of resistivities to be used in the design of the earthing system shall be subject to the Engineer’s approval.



C. The surveys shall show the variation of resistivity across the site and with the depth below the site. The Contractor shall consider if there is a need to model the resistivity in two layers and if there is any advantage in the use of long rods. The surveys shall also determine the depth and nature of any underlying rock, which may limit the depth for driving earth rods or if boring will be necessary for installing earth rods.

D. The weather conditions prior to and at the time of the surveys shall be recorded in the report and an assessment made of the seasonal variations in resistivity based on meteorological data for the area. The program for the project should, as far as possible, time the resistivity surveys to take place during a dry season.

E. The report should also state if there are any indications that the ground is corrosive to copper or if there is any risk of galvanic corrosion on other metal structures in the neighborhood.

F. The report shall be approved by the Engineer before proceeding with the design of the earthing system.

G. The calculations shall be submitted for approval prior to commencing the design of the earthing systems.

2.3 FAULT CURRENT AND DURATION

A. The earthing system design calculation by the Contractor shall be based on earth fault withstand current shown in DEWA General Design Criteria Standard 1.1.0.0.0.01.

B. The estimated maximum duration of the fault current shall not be less than 5.0 seconds for the 11kV system.

2.4 EARTH ELECTRODE SYSTEM DESIGN

A. Design Calculations:

1. The design of the earth electrode systems shall be based on the approved earth resistivity data and the system’s fault currents and their duration.

2. The design calculations shall be to the approval of the Engineer and shall be based on the methods given in the standards listed. The calculations shall include the following parameters:-

a. Earth resistance of the whole system of its components.b. Earth potential rise.c. Step, touch and mesh potentials inside and outside the perimeter fence.d. Requirements for a high resistance surface layer.e. Conductor ratings.

3. The earth potential rises shall not exceed the ITU limits appropriate to the classification of the system unless special precautions are taken to cater for transferred potentials.

4. Step, touch and mesh potentials shall be within the limits calculated in accordance with the standards given in IEEE 80 and BS 7430 for the proposed surface layer. The formula for allowable body current shall be used for 50 Kg body weight.

B. Earth Electrode:



1. The earth electrodes shall comprise a system of bare conductors forming a mesh buried near the surface of the ground supplemented, as necessary, by one or more of the following electrodes: a. A system of interconnected steel rods driven into the ground.b. Structural steel metalwork in direct contact with the ground.c. Reinforcing steel in buried concrete.

C. Mesh System:

1. The mesh system shall be designed in accordance with paragraph A "Design calculations" above to limit touch, step and mesh potentials taking into account the combined length of the mesh conductors, other buried conductors and rods but excluding any buried conductors outside the perimeter fence. Due regard shall be given to non-linear distribution of the fault current giving rise to the highest potentials at mesh corners.

2. The rating of the mesh conductors shall be compatible with the fault currents after allowing for parallel paths with a minimum conductor size of 300 mm2 copper.

3. The current division factors = 0.8 of given fault current shall be taken for design calculations of ground mesh.

4. If the placement of earthing mesh is designed for outside of the building, the depth of mesh shall be 2 m below the ground level or this shall be at least 1 m below the power cables of standard depth.

D. Interconnected Rods:

1. If the design calculations show that a mesh alone is unable to limit the potentials to the required values, then the mesh shall be supplemented by the use of interconnected earthing rods driven into the ground or installed in bored holes.

2. Rods shall be installed inside the perimeter fence to enclose the maximum possible area compatible with the earthing of any metallic fence. (The spacing between rods shall not be less than their length, unless rating considerations determine otherwise). The rods shall be interconnected in groups of 4 to 10 rods by yellow-green colored PVC insulated stranded copper conductors to form a ring. Each group shall be connected to the mesh by duplicate insulated copper conductor via disconnecting test links.

3. Individual rods may be connected directly to the mesh provided the conductor to the rod can be disconnected for testing the rod.

4. Rods installed in bored holes may be used to reach lower resistivity ground strata at depths beyond the reach of driven rods or where rock is encountered and it is not possible to drive rods. After installing the rod the bored hole shall be back-filled with a low resistivity liquid mixture that shall not shrink after pouring to ensure good contact between the rod and the ground for the life of the installation.

5. The resistance and rating of individual rods and the combined resistance of the groups of rods in the proposed design shall be calculated and the rating of the interconnecting conductors shall not be less than that of the main grid conductor.

6. The calculation of potentials in the design of the complete installation shall be made without the group of rods with the lowest estimated resistance to simulate the condition with the group disconnected for testing.

E. Reinforcing Steel:

1. The reinforcing steel in the foundations of buildings containing the primary electrical equipment may be used as auxiliary electrodes subject to the approval of the



Engineer. The Contractor shall show in the design calculations that the fault currents and d.c. stray currents will not damage the structure.

2. Steel reinforcing mesh in the floors of the building may also be used for the control of step and touch potentials within the building subject to the approval of the Engineer.

F. Conductors Outside Perimeter Fence:

1. If the design calculations show that the step and touch potentials outside the perimeter fence, gate or wall exceed the limits then additional bare conductors shall be buried in the ground outside the fence in the form of rings encircling the whole site.

2. The distance of the conductors from the fence and the depth shall be determined in the design to ensure that step and touch potentials are within the limits.

3. The minimum conductor size shall be 70 mm2 and shall be connected to the fence or the mesh with 70 mm2 conductors at each corner of the site and at intervals of not more than 100 m. These conductors shall not be included in the calculations called for above.

2.5 GENERAL REQUIREMENTS

A. Component parts of earthing system are to include the following:

1. Earth electrode (rods, tapes etc.)2. Main earthing terminals or bars.3. Earthing conductors.4. Protective conductors.5. Equipotential bonding conductors.6. Electrically independent earth electrodes for special systems (clean earth).7. Accessories and termination fittings, bonding, welding kits and other materials.

B. Earth electrode is to consist of one or more earth rods, interconnected by buried earthing tape or cable, which is to have a total combined resistance value, during any season of the year and before interconnection to other earthed systems or earthing means, not exceeding 1 ohm. Distance between 2 rods is not to be less than 6 meters.

C. Main ring earthing resistance should not exceed 1 ohm.

D. Ring type earth electrode is to consist of earthing conductors, in a closed loop, buried in exterior wall foundations underneath the water-proofing, or alternatively at 0.6 m around the perimeter of the building foundations, as shown on the Drawings. Connect all earthing conductors to this ring. Insulated connection flags into the building, of same material as earthing conductors, are to be located at positions of service entrance and main switchboard rooms, terminating in bolt-type earth points (studs) or test links for connection of main earth bar(s). Additional earth rods connecting with the earth ring are to be provided, as necessary, to bring down earth electrode resistance to an acceptable value.

E. Functional earth electrode is to be provided separately from, but interconnected to, other earth electrode(s) through suitably rated (470 V) spark gap. Functional earth electrodes are to be used for earthing electronic equipment (communication equipment, digital processors, computers etc.) as required by the particular Section of the Specification and recommendation of the manufacturer.

F. Alternative Earth Electrode: Other types of earth electrode may be used, after approval, including:



1. Copper plate(s)2. Tape mats (strips).

G. Main earthing bar is to be provided at point of service entrance or main distribution room, and as described in the Specification or shown on the Drawings. Connect all earthing conductors, protective conductors and bonding conductors to the main earthing bar. Provide 2 insulated main earthing conductors, 1 at each end of the bar, connected via testing joints to the earth electrode at 2 separate earth pits. Conductor is to be sized to carry maximum earth fault current of system at point of application with final conductor temperature not exceeding 160 deg. C (320 deg. F) for at least 5 seconds. Main earthing conductors are to be minimum 120 mm2 or as otherwise required by the particular Section of the Specification. Main earthing bar shall be positioned at an accessible location within the electrical room and clearly labeled.

H. The main earth bar shall be in the form of a ring or rings of bare conductors surrounding or within an area in which items to be earthed are located. Where 2 or more rings are installed they shall be interconnected by at least two conductors, which shall be widely separated.

I. Testing joints (test links) are to be provided, in an accessible position, on each main earthing conductor, between earthing terminal or bar and earth electrode.

J. Protective conductors are to be separate for each circuit.

1. Selection of sizes is to be in accordance with Table 54F of IEE Regulations.

K. Protective conductors are not to be formed by conduit, trunking, ducting or the like.

L. Continuity of Protective Conductors: Series connection of protective conductor from one piece of equipment to another is not permitted. Extraneous and exposed conductive parts of equipment are not to be used as protective conductors, but are to be connected by bolted clamp type connectors and/or brazing to continuous protective conductors which are to be insulated by molded materials.

1. Conductor sheaths shall be of yellow-green colored PVC to meet the requirements of BS 6004 or IEC 60502-1 Grade ST1 with a minimum thickness of 1.5 mm.

M. Bare strip conductors only shall be used for earth electrodes or voltage control meshes.

N. Conductors buried in the ground shall normally be laid at a depth of 1000 mm below the underground power cables in an excavated trench. The backfill in the vicinity of the conductor shall be free of stones and the whole backfill shall be well consolidated.

O. All conductors not buried in the ground shall be straightened immediately prior to installation and supported clear of the adjacent surface.

P. Earth Fault Loop Impedance: For final circuits supplying socket outlets, earth fault impedance at every socket outlet is to be such that disconnection of protective device on over-current occurs within 0.4 seconds. For final circuits supplying only fixed equipment, earth fault loop impedance at every point of utilization is to be such that disconnection occurs within 5 seconds.

1. Use appropriate tables and present same for approval by the Engineer (IEE Regulations: Tables 41A1 and 41A2, Appendix 7 and Regulation 543).



Q. Supplementary Equipotential Bonding: Connect all extraneous conductive parts of the building such as metallic water pipes, drain pipes, other service pipes and ducting, metallic conduit and raceways, cable trays and cable armor to nearest earthing terminals by equipotential bonding conductors. Cross-section of protective bonding conductor shall not be less than ½ of the protective conductor connected to respective earthing terminal with a minimum of 4 mm².

1. Individual components of metallic structures of plant shall be bonded to adjacent components to form an electrically continuous metallic path to the bonding conductor.

2. Small electrically isolated metallic components mounted on non-conducting building fabric need not be bonded to the main earth bar.

3. Bolted joints in metallic structures including pipework, which do not provide direct metallic contact shall be bridged by a bonding conductor or both sides of the joint shall be separately bonded to earth unless the joint is intended to be an insulated joint for cathodic protection or other purposes.

R. Main Equipotential Bonding: Main incoming and outgoing water pipes and any other metallic service pipes are to be connected by main equipotential bonding conductors to main earth terminal or bar. Bonding connections are to be as short as practicable between point of entry/exit of services and main earthing bar. Where meters are installed, bonding is to be made on the premise side of the meter. Cross-sections of conductors are not to be less than ½ that of the earthing conductor connected thereto, and minimum 6 mm².

S. Identification: Connection of every earthing conductor to earthing electrode and every bonding conductor to extraneous conducting parts is to be labeled as follows, in accordance with the Regulations.

T. Identification: Protective and earthing conductors are to be identified by combination of green-and-yellow colors of insulation or by painting bar conductors with these colors, as approved.

U. Identification: Source earthing conductor (or neutral earthing conductor) is to be identified along its entire length by continuous black insulation labeled 'neutral earthing'. The neutral earthing ground rod pit is to be also clearly identified.

V. Exposed external earth / grounding conductor connection joints are to be protected from corrosion with grease caps or Denso tape (bituminous tape) or approved equal.

W. The earthing and lightning protection system for any new extension shall be suitably connected to the existing system.

X. In general earthing conductor connections to structures, connections within the lightning protection system conductors, are to be exothermic copper-weld type unless stated otherwise.

2.6 GROUNDING CONDUCTORS

A. Buried Earth Conductors: PVC insulated copper strip conductors or PVC insulated stranded copper cables with cross-section min 70 mm2 or as per earthing calculation.

B. Earthing Conductors: PVC insulated copper conductor as described in the Specification for the particular application.



C. Protective Conductors: Single core stranded annealed copper, PVC insulated cables, having rated insulation grade compatible with circuit protected, or to be a conductor forming part of a multi-core cable, yellow/green color.

D. All conductor fittings shall be manufactured from high strength copper alloys with phosphor bronze nuts, bolts, washers and screws. Binary brass copper alloys will not be acceptable. All fittings shall be designed for the specific application and shall not be permanently deformed when correctly installed.

E. Protective Bonding Conductors: PVC insulated copper strip conductor, annealed stranded copper cable or flexible strap (flexible braid) of cross-sectional area as described in Article "General Requirements" hereof.

F. Main Earthing Bar: Tinned, 40 x 4 mm where formed into a closed loop, and 50 x 6 mm where open-ended. Earth bar is to be labeled 'Main Earth Bar' and is to be drilled, for connection of conductors, at a spacing not less than 75 mm, and is to be supplied with copper alloy bolts, nuts and washers and wall mounting insulators.

G. Disconnecting links shall comprise a high conductivity copper PVC insulated link supported on two insulators mounted on a galvanized steel base for bolting to the supporting structure. The two conductors shall be in direct contact with the link and shall not be disturbed by the removal of the link. Links for mounting at ground level shall be mounted on bolts embedded in a concrete base.

H. Disconnecting links mounted at ground level and the connections at the earth rods shall be enclosed in concrete inspection pits, with concrete lids, installed flush with the ground level.

2.7 CONNECTOR PRODUCTS AND EARTHING ACCESSORIES

A. Copper or copper alloy, purpose made, of approved design, compatible with points of connection, and of adequate cross-section and current carrying capacity.

B. Connections to metallic structures for earthing conductors and bonding conductors between electrically separate parts of a structure shall be either by direct exothermic welding or by bolting using a stud welded to the structure. Drilling of a structural member for a directly bolted connection shall only be carried out to the approval of the Engineer.

1. Bolted Connectors and Clamps: Bolted-pressure-type connectors and clamps, or compression type. Bolts, nuts and washers are to be high quality phosphor bronze or copper silicon alloys. Bolted connections are not permitted in run of the earthing conductors unless approved by the Engineer.

2. Welded Connectors: Exothermic-welded type, in kit forms, and selected per manufacturer's written instructions. Welded connectors are to be used only in inaccessible locations and at “T” joints, to the approval of the Engineer.

C. Bi-metallic connectors shall be used between conductors of dissimilar materials and insulating material shall be interposed between metallic fittings and structures of dissimilar materials to prevent corrosion.

D. When the reinforcing in concrete is used as a part of the earthing system the fittings used to provide a connection point at the surface of the concrete shall be exothermically welded to a reinforcing bar. This fitting shall be provided with a bolted connection for an earthing conductor. The main bars in the reinforcing shall be welded together at intervals to ensure electrical continuity throughout the reinforcing.



E. No connections shall be made to reinforcing bars and other steelwork, which do not form part of the earthing system and are completely encased in concrete.

2.8 GROUNDING ELECTRODES

A. Ground Rod: 16 mm diameter stainless steel. Driving head is to be high strength steel. Couplings are to be long length silicon bronze, internally threaded. Threads are to be rolled onto rod to ensure uniform layers of copper and strength. Earth rod is to be complete with non-corrosive couplings, head and bolted connector of sufficient size, and number of bolted clamps to connect all cables terminated thereto.

1. Minimum Length of Rod: 3.6 m, extendible as necessary to obtain required earth resistance

2. Rods, and driving caps and tips shall abut at couplings to ensure that the couplings and screw threads are not subject to driving forces. All screw threads shall be fully shrouded at the couplings.

B. Tape Mats: Where earth rods are not likely to be used, earth electrode is to consist of parallel and perpendicular copper strip, 2.4 m apart, welded together by exothermic welds to form a grid. Tape is to be 25 x 2.5 mm strip conductor.

C. Earth Pit: Precast, square or circular section concrete handhole (minimum 450 mm internal diameter), with ultra heavy-duty cover for areas where heavy vehicles cross, and extending to about 150 mm below top of earth rod. Earth pit is to be provided for each earth rod where connected to an earthing conductor. Earth pit body is to have inset stainless steel plate with inscription 'Earth Pit Nº # & Earth pit ID - Do Not Remove'.

PART 3 - EXECUTION

3.1 TRANSFORMER SUBSTATION EARTHING

A. MV switchgear and MV cables are to have separate main earthing bar connected to framework or earth bar of each item by insulated conductor and the earth-electrode by 2 insulated earthing conductors, one at each end of bar, via testing joints. Earthing conductor is to be minimum 150 mm².

B. Outdoor ring main units, which are individually mounted, are to be connected to earth by 2 insulated earthing conductors, bolted at earthing terminal.

C. LV switchgear is to have separate main earthing bar connected to framework or earth bar of each item by insulated conductor.

D. Main LV switchgear panel is connected to main LV Earth bar in electrical room which in turn connected at two ends by 2 insulated earthing conductors through testing joints to two earth pits. Earthing conductor size is to be minimum 150 mm².

E. Transformer body earthing terminal is to be connected to MV main earthing bar by insulated copper earthing conductor not less than 20 mm² per 100 kVA of transformer rating, with a minimum of 35 mm².

F. Transformer neutral (star point) is to be connected by insulated earthing conductor (colour black) directly to independent earthing electrode. Neutral earthing conductor is to be sized



for maximum earth fault current for 5 seconds with final conductor temperature not exceeding 160 deg. C or sized not less than 30 mm² per 100 kVA of transformer rating, and with a minimum of 50 mm².

G. Outdoor package substation earthing is to comprise at least 4 earth rods, each providing a connection point of an earthing conductor connected to one end of the earthing bars at MV and LV switchgear sections respectively. The 4 rods are to be interconnected together and to the earth electrode.

H. Lightning arresters are to be directly connected to the earth electrode, following the shortest path. Each lightning arrester is to be connected at a dedicated earth rod.

3.2 EARTHING OF MAIN DISTRIBUTION BOARDS, PANELBOARDS, LIGHTING INSTALLATIONS AND WIRING ACCESSORIES

A. Main earthing bar is to be provided in main distribution room and connected to earth electrode by 2 insulated conductors (minimum 150 mm²) via testing joints.

B. Earthing bars of main distribution boards are to be connected, by insulated earthing conductor, directly to main earthing bar at main distribution room.

C. Distribution, lighting and power panelboards are to be connected by protective conductors run together with incoming feeder cable, connecting earth terminals in panelboards with respective main distribution board earthing bar.

D. Socket outlets are to be earthed by protective conductor looped around with the branch circuit and connected to earth terminal within socket outlet box and to which socket outlet terminal is to be connected.

E. Final Ring Sub-circuits: Protective conductor of every final ring sub-circuit is to be in the form of a ring having both ends connected to earth terminal at origin of circuit in panel board.

F. Lighting fixtures and other exposed conductive parts of electrical installations, such as switches, heaters, air conditioning units etc. are to be connected by protective earth conductors to earthing terminals of respective panelboards.

3.3 ELECTRICAL / MECHANICAL PLANT ROOMS AND FIXED MACHINERY

A. Main earthing bar or loop is to be conveniently located in electrical/mechanical plant rooms, and connected by earthing conductors to exposed conductive parts of motor control centre at its earthing bar, and to motors, switches and other electrical equipment etc. at their earthing terminals, using 20 x 2 mm insulated copper strips or 35 mm² insulated copper conductor (minimum size) or as required to carry maximum earth fault current for 1 second with final conductor temperature not exceeding 200 deg. C (392 deg. F).

B. Conductors are to be securely fixed, recessed in floor grooves or niches, or fixed to walls by appropriate staples. Earth bar or loop is to be securely fixed to building wall with copper or brass saddles.

C. Main earthing bar or loop is to be connected at 2 extremely separate points to earth electrode, directly through 2 test joints by insulated earthing conductors, or connected to main earth bar by protective conductors.



D. Motor and other equipment earth terminals are to be connected also by protective earth conductors of each branch circuit to earth terminal/bar at motor control centre, panel or distribution unit.

3.4 ROAD LIGHTING

A. Earthing Cables: Separate protective earthing cables for lighting column circuits are to be run with power circuit, terminated at LV supply position in lighting control panel and looped into column earthing terminals. The last column is to be bonded via an earthing bolt to a single 16 mm diameter stainless steel rod, 3.6 m long, driven into ground adjacent to column. Bonding is to be 16 mm² stranded bare copper conductor.

B. Connections between rods and earthing conductors are to be made by the Cadweld process producing a fused joint. Bolted connections may be used for connection to removable items of equipment only.

3.5 SIGNAL AND COMMUNICATION SYSTEMS

A. Signal and Communication Systems: For telephone, alarm, voice and data, and other communication systems, provide 16 mm² minimum insulated grounding conductor in raceway from a separate grounding electrode clean system to each service location, terminal cabinet, wiring closet, and central equipment location.

1. Service and Central Equipment Locations and Wiring Closets: Terminate grounding conductor on a 6.4 by 50 by 300 mm grounding bus.

2. Terminal Cabinets: Terminate grounding conductor on cabinet grounding terminal.

3.6 CLEAN EARTH GROUNDING

A Clean earth grounding or low noise earth shall be provided as required, to ensure that the level of induced or conducted interference from external sources, including the facility power grounding system, does not produce incidence of malfunction of the equipment, which is unacceptable for the operating system.

B Clean earth grounding system shall not be connected to any other earthing or grounding system.

C Clean earth grounding cables shall not be run parallel with other grounding cables or power cables.

D Clean earth grounding system shall comply with IEC 60950 and BS EN 50310.

E Clean earth grounding pits shall be separated from other earthing pits by a distance of at least 1800mm.

F In general clean earth grounding shall be provided for date system, telephony and other communication systems, and UPS.

G Clean earth grounds shall have an earth impedance of less than 1 ohm.

3.7 EARTHING AND BONDING MULTICORE CABLES

A. The metallic sheath and armor of multicore cables shall be bonded together and earthed.



B. Cable earthing conductors shall be copper strip with appropriate section laid in formed cable trenches or ducts, or fixed to walls, concrete or steel work, by means of clamps or claw type cleats, appropriately secured into suitable wall plugs or tapped holes. The spacing of fixings shall not be greater than 1 m. Where earth strip is buried or laid in positions in which there is danger of corrosion it shall be provided with a corrosion-proof serving of extruded thermo-plastic or self-adhesive PVC tape which for short lengths may be hand applied on Site.

C. The Contractor shall connect, unless otherwise instructed, all cable sheaths and armor, supporting steel work and the metal enclosure of sealing boxes, joints, etc., to the main earth bar by suitable branch connections which may be of bare or insulated stranded conductor as required to suit the cable system.

D. Concentric type bonding leads of suitable impedance shall be employed where necessary . The bonding and earthing system shall be subject to the approval of the Engineer and shall be designed to meet the subsequent maintenance requirements.

3.8 EARTHING OF FENCES

A. Method: Metallic fences shall be separately earthed unless they come within 1.8 m of any equipment or structure above the surface of the ground, which is connected to the main earthing system. If the separation of 1.8 m cannot be obtained the fence shall be bonded to the earthing system.

B. Separately Earthed Fences: The earthing of a fence shall be provided by connecting certain metallic fence posts to an earth rod by a copper conductor. The earth rod shall be driven adjacent to the posts inside the fence line to a depth of not less than 3.0 m. Where no metallic posts are provided the earth rods shall be connected directly to the metal wires, mesh or other components of the fence.

C. Bonded Fences: Fences which need to be bonded to the main earthing system of the installation shall be connected by copper conductors to the nearest accessible point on the main earthing system at each point where the fence comes within 1.8 m of any electrical equipment. Bonds shall also be made to each corner post, below the outer phase conductors of overhead line connections passing over the fence, at each gate and at intervals of not more than 100 m.

D. Bonding of Fence Components:

1. Fences made up of bolted steel or other metallic components do not require bonding between components. Where such fences have non-metallic components bonds shall be installed to maintain continuity between metallic components. Reinforced concrete components shall be treated as being non-metallic.

2. Longitudinal wires for supporting other fence components or for anti-climbing guards and the wires of chain link shall be directly bonded to each fence earth electrode or to each bond to the main earthing system.

3. Metallic components on masonry, brick, concrete or similar boundary wall shall be treated in the same manner as metallic fences.

4. Wire fence components coated for anti-corrosion protection or PVC coated fence shall be earthed in accordance with this Clause.

E. Gates: The fixed metallic components on both sides of the gate shall be directly bonded together by a copper conductor installed under the surface of the access way. Flexible



conductors shall be installed to bond the moving parts of the gates to the metallic fixed parts. An earth rod or a bond to the main earthing system shall be installed at each gate.

F. Potential Control Outside Fences:

1. Where the approved design calculations show that the touch or step potentials outside the fence or boundary wall would otherwise be excessive, bare copper conductors shall be buried in the ground outside the fence or boundary wall at such depths and spacings as are shown in the approved design calculations to give acceptable touch and step potentials. The conductors shall form complete rings surrounding the installation and each ring shall be bonded to the adjacent ring and to the fence at each corner. Below the outer phase conductors of overhead line connections passing over the fence, at each gate and at intervals of not more than 100 m. In this case separate earth electrodes are not required for the fences.

2. If the boundary fence or wall is substantially non-metallic the rings of conductors shall be bonded to the main earth system at each corner of the site and at intervals of not more than 100 m. Any metallic components on such boundary fences or walls shall be bonded to the earthing system in accordance with this Specification.

3. If the boundary fence is metallic and is not within 1.8 m of any part of the main earthing system or equipment bonded thereto the fence and outer conductor rings shall not be connected to the main earthing system unless the approved design calculations show otherwise.

4. Any meshes formed by bonding the outer conductors to the main earthing system shall be sub-divided by additional conductors, if required, to give acceptable touch, step and mesh potentials.

G. Conductors: All conductors used for earthing and bonding the fences and components and for outer rings shall have a cross-sectional area of not less than 185 mm2 copper.

3.9 INSTALLATION GENERAL

A. Continuity: Ensure that complete earthing system is electrically continuous and mechanically secure.

B. Locations of main earth bars in substations, electrical rooms, mechanical rooms, hub rooms, etc., to be clearly identified by 100mm X 100mm white traffolyte labels, with red lettering, to Engineer’s approval.

C. Main earth bars to be provided in all electrical rooms, hub rooms and plant rooms, located so as to be easily accessible and protected by a 2mm thick aluminium plate against inadvertent damage.

D. Earth Rods: While siting earth rods, ensure that resistance areas associated with individual rods do not overlap. Earth rods are to be located at a distance greater than 600 mm from foundations of buildings. Where rock is encountered, a hole of sufficient size is to be drilled before lowering the rod. Conductive filler such as Marconite or Bentonite or equal filler that will not corrode is to be provided around the rod.

E. The rods shall be installed by driving into the ground with a power hammer of suitable design to ensure the minimum of distortion to the rod. Where it is not possible to drive rods to the full depth required due to the presence of a stratum of rock, then holes shall be drilled or blasted in the rock. The holes shall be filled with bentonite or other approved material prior to inserting the rod.



F. Spacing between earth rods shall not be less than that stipulated by the IEC.

G. Buried earthing conductors are to be laid at a depth not less than 0.8 m from ground surface.

H. Earthing conductors are to follow shortest path between earth rods and main earthing terminals or bars, and are to run in PVC conduit (duct) fastened to building structure by approved supports and extending 0.2 m above level, and are to be protected against mechanical damage and corrosion.

I. Protective Conductors: Separate protective conductors, which are not part of a cable, are to be fixed on same support or drawn into same conduit as circuit conductors.

J. Protective Bonding: Remove any non-conductive paint, enamel or similar coating at threads, contact points and surfaces and ensure that bonding is made by fittings designed to make secure bonds.

K. The diameter of any holes drilled in strip conductors shall not be greater than half the width of the strip.

L. Connections to electrical equipment shall be detachable and made at the earthing studs or bolts provided on the equipment by the manufacturer. When an earthing point is not provided the point and method of connection shall be agreed with the Engineer.

3.10 CONNECTIONS

A. Protection against Corrosion: Protect bolted connections against corrosion either by filling with vaseline or coating with a special anti-corrosion compound and proper capping (Denso tape / grease caps).

B. Connections: Earth connections are to be readily accessible. If inaccessible earth connection is permitted, approved exothermic welding or brazing technique is to be employed.

C. Connections: Where earth connections between dissimilar metals must be made, use bimetallic fittings and protect by coating with moisture resisting bituminous paint or compound, or by wrapping with protective tape to exclude moisture.

D. Exothermic-Welded Connections: Comply with the manufacturer's written instructions. Welds that are puffed up or that show convex surfaces indicating improper cleaning are not acceptable.

E. Tighten screws and bolts for grounding and bonding connectors and terminals according to the manufacturer's published torque-tightening values. If the manufacturer's torque values are not indicated, use those specified in applicable Standards.

F. Connection of earthing conductors to Ground pit earth rods, shall utilize multiple connectors as required. More than one cable shall not be connected through one connector clamp unless specifically permitted.

3.11 FIELD QUALITY CONTROL

A. Combined resistance of earth electrodes is to be measured during dry season and checked against specified resistance.



B. Excessive Ground Resistance: If resistance to ground exceeds specified values, notify the Engineer promptly and include recommendations to reduce ground resistance.

C. Electrical continuity of all earthing and protective conductors including main and supplementary equipotential bonding conductors is to be checked.

D. Earth fault loop impedance of all circuits is to be measured and checked against calculated impedance figures.

E. Operation of residual current protective devices is to be checked.

F. Field tests shall include all tests as per NETA.

G. All test records shall be numbered and certified.

3.12 GRADING AND PLANTING

Restore surface features, including vegetation, at areas disturbed by Work of this Section. Reestablish original grades, unless otherwise indicated. If sod has been removed, replace it as soon as possible after backfilling is completed. Restore areas disturbed by trenching, storing of dirt, cable laying, and other activities to their original condition. Include application of topsoil, fertilizer, lime, seed, sod, sprig, and mulch. Comply with Division 2 Section 02900 "Landscaping." Maintain restored surfaces. Restore disturbed paving as indicated.

END OF SECTION 16060


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