260526_Earthing_Systems_TechSpecs_JULY_2012.pdf

26 05 26: Grounding and Bonding Specification

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JULY 2012 (100% FINAL)

Grounding and Bonding

Technical Specs

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JULY 2012 (100% FINAL)

1- GENERAL

SUMMARY

A. This Section includes requirements for complete installations to provide protective earthing and equipotential bonding, based on the TN-S system arrangement, including:

1. Main earthing terminals or bars.

2. Exposed conductive parts of electrical equipment.

3. Extraneous conductive parts.

4. Separate clean earth for ELV (Extra Low Voltage) Systems and control rooms to be less than (0.5) ohm.

B. This Section also includes complexity installations to avoid electromagnetic incompatibility that can affect the operation of sensible electronic equipment.

DEFINITIONS

A. The following terms used in the Specification 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, 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.

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J. Earthing Conductor:

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

SUBMITTALS

A. Product Data:

Prior to ordering materials, submit data for approval including, but not limited to, manufacturer's catalogues 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 to demonstrate their capabilities and experience. Include lists of completed projects with project names and addresses, names and addresses of architects engineers and owners, and other information specified or required by owner.

C. Field Test Reports:

Submit 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. Exact location of earth pits, rods and details of installation and connections.

2. Exact routing of buried earthing conductors with indication of cross-section, depth of laying and covering.

3. Cross sectional area of all earthing, protective and bonding conductors.

4. Layout and details of earthing provisions at substations, generator rooms, switchgear, distribution panel boards etc., indicating fittings used, insulation, plates and marking, passage and routing of earthing conductors, conduit, sleeves, grooves, niches etc., giving sizes and dimensions of component parts.

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

E. Records:

Submit the following:

1. Scaled drawings, as-installed, showing actual layout and specification of all components of earthing system.

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.

G. Final earthing design calculations for approval.

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STANDARDS & QUALITY ASSURANCE

A. Installer Qualifications: Engage an experienced installer who has specialized in installing earthing systems similar in material, design and extent to those indicated for this Project and whose work has resulted in installations with a record of successful in-service performance.

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

1. IEC 60364- 1 and 60364-4-41: Electrical Installations in Buildings.

2. BS 7671 Requirements for Electrical Installations (IEE Wiring Regulations 17th Edition).

3. BS 7430: Code of Practice for Earthing.

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

C. Products shall be sourced either directly from manufacturer or from the manufacturer's authorized dealer agent.

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JULY 2012 (100% FINAL)

2- PRODUCTS AND SYSTEMS

MANUFACTURERS:

A. Approved Manufacturers: Subject to compliance with requirements, provide products by one of the following.

SOIL SURVEY AND CALCULATIONS

A. The Contractor shall carry out an earth resistivety survey on each site and report in writing to the owner. 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 owner’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 neighbourhood.

F. The report shall be approved by the owner 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.

FAULT CURRENT AND DURATION

A. The earthing system design calculation by the Contractor shall be based on earth fault withstand current.

B. The estimated maximum duration of the fault current shall not be less than 1 second for a three phase fault current of 40kA.

1. Furse (UK)

2. Helita (France)

3. Wallis (England)

4. ERICO (USA)

5. Thompson Lightning Protection, Inc. (USA)

6. Approved Equal EU/USA

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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. Ring (loop) earthing resistance should not exceed:

1. 1 Ohm for “Ring Main Units”

2. 2 Ohm for the “Power Earthing” (Transformer Neutral or Generator Neutral)

C. Main earthing bar is to be provided at point of service entrance, and as described in the Specification and drawings. Connect all relevant earthing conductors and bonding conductors to the main earthing bar. Provide 2 main earthing conductors (insulated where specified), 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° C for at least 1 second. Main earthing conductors are to be minimum 95 mm2 or as otherwise required by the particular Section of the Specification or as indicated on design drawings. Main earthing bar shall be positioned at an accessible location within the electrical room and clearly labelled.

D. In Electrical or equipment rooms where EMC is required, the main earth bar shall be in the form of a ring or rings of bare conductors surrounding the room, 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.

E. 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.

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

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

H. 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 (or as indicated on the design drawings).

I. Earthing conductor sheaths shall be of yellow-green coloured PVC.

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

K. 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.

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

M. 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.

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JULY 2012 (100% FINAL)

N. Identification: Protective and earthing conductors are to be identified by a combination of green-and-yellow colors.

O. Exposed external earth 1 grounding conductor connection joints are to be protected from corrosion with grease caps or Denso tape ( bituminous tape) or approved equal.

GROUNDING CONDUCTORS

A. Buried Earth Conductors: PVC insulated (or bare as per indication on design drawings) copper strip conductors or

PVC insulated (or bare as per indication on design drawings) stranded copper cables with cross-section min 95 mm2 or as per earthing calculation (after approval).

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 colour.

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 specified.

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.

6. 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.

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 (preferred) 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 form, 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 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.

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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 (rebar). 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 steel work which do not form part of the earthing system and are completely encased in concrete.

GROUNDING ELECTRODES

A. Ground Rod: at least 16 mm diameter high strength, low carbon steel core of high tensile strength (600 N/mm2), grade 43 A of BS 4360, with 99.99% pure electrolytic copper molecularly bonded in to steel core, 0.25 mm thickness. 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: 2.4 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 hand-hole (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. Hand-hole body is to have inset stainless steel plate with inscription: "Earth Pit No # & Earth Pit ID - Do Not Remove". Pit cover shall be painted in Green and Yellow colors for easy identification as an earth pit.

ELECTROMAGNETIC COMPATIBILITY

A. The "IT equipment room" shall be treated in a special way to avoid the risks of electromagnetic incompatibility.

B. the work to be delivered in this work package includes, for each room:

1. The realization of a low-level girdle around the edge of the room, at 0.20 m from the floor, in tinned copper strip, 30 x 2 mm, fixed at three points per meter.

2. The realization of a high-level girdle around the edge of the room, at 0.20 m from the ceiling (above false ceiling where applicable), in tinned copper strip, 30 x 2 mm, fixed at three points per meter.

3. The realization of a vertical interconnection between the two girdles, at each corner of the room, in tinned copper strip, 30 x 2 mm, fixed at three points per meter.

4. The supply and fixture of an equipotential bar in copper on insulating supports every 5 meters around the sides of the room at 0.20 meters above the floor and connected to the lower girdle.

5. The realization of a ground plane interconnection of the room with the rest of the grounding system by tinned copper strip, 30 x 2 mm (forming a mesh 0.6m x 0.6m), including the interconnection of the concrete reinforcement.

6. The work, apart from supplies, should also include all the implementation suggestions (the brass nuts and bolts, hard silver soldered joints etc.)

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JULY 2012 (100% FINAL)

3- EXECUTION

TRANSFORMER SUBSTATION EARTHING

A. MV Ring Main Units are to have separate main earthing bar connected to framework of the Ring Main Unit or earth bar of each item by insulated (or bare as per indication on design drawings) conductor. The main earthing bar shall be connected to the earth electrode system at two different pits by 2 insulated (or bare as per indication on design drawings) earthing conductors, one at each end of bar, via testing joints. Earthing conductor is to be minimum 70 mm2.

B. Main LV switchgear is to have separate main earthing bar connected to the earth bar of the LV switchgear by insulated

(or bare as per indication on design drawings) conductors, one at each end of bar, via testing joints. Earthing conductor is to be minimum 70 mm2.

C. Transformer body earthing terminal is to be connected to Ring Main Unit main earthing bar by insulated copper earthing conductor not less than 2 conductors each 70mm2.

(if conductor size is not indicated use no less than 20 mm2 per 100 kVA of transformer rating, with a min. of 35 mm2)

D. Transformer neutral (star point) is to have separate main earthing bar connected to the Low Voltage Neutral Terminal of the transformer by insulated (or bare as per indication on design drawings) conductor. The main earthing bar shall be connected to the earth electrode system at two different pits by 2 insulated (or bare as per indication on design drawings) earthing conductors, one at each end of bar, via testing joints. Earthing conductor is to be minimum 70 mm2.

If insulated earthing conductor is used the color of the sheath shall be Grenn/Yellow. Transformer neutral point shall be connected directly (or via dedicated main earth bar) to independent earthing electrode system. Neutral earthing conductor is to be sized for maximum earth fault current for 5 seconds with final conductor temperature not exceeding 160°C. (if earthing conductor size is not indicated, it shall be sized not less than 30 mm2 per 100 kVA of transformer rating, and with a minimum of 50 mm2).

E. Lightning arresters (where applicable) 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.

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 bar of the Main LV Switchgear by by 2 insulated conductors each 70mm2 via testing joints.

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

C. Distribution, lighting and power panel-boards are to be connected by protective conductors run together with incoming feeder cable, connecting earth bars/terminals in panel-boards 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 (to respective panel-board earth bar).

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 panel-boards. Earth conductor shall be run together with power feeder (cable).

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JULY 2012 (100% FINAL)

GENERATOR EARTHING

A. Generator neutral (star point) is to be to connected to a separate main earthing bar connected to the generator Neutral

Terminal by insulated (or bare as per indication on design drawings). The main earthing bar shall be connected to the earth electrode system at two different pits by 2 insulated (or bare as per indication on design drawings) earthing conductors, one at each end of bar, via testing joints.

Generator neutral shall be connected through the neutral earthing link or device to separate earthing bar. Neutral earthing conductor is to be suitably sized to carry maximum earth fault current for time it takes the system protection to operate with final conductor temperature not exceeding 160°C, but not less than 30 mm2 per 100 kVA of generator rating, with a minimum of 50 mm2. (Refer to design drawings for design earthing conductor size).

B. Generator earthing terminal is to be connected to main earthing bar by insulated copper conductor of cross section not less than 20 mm2 per 100 kVA of generator size, with a minimum of 35 rnm2.

C. Switchgear (ATS) and Control Gear: Earthing terminals or bars of switchgear and control gear are to be connected by separate protective conductors to respective normal and emergency main distribution board earth bars. Protective conductor shall be run with and in close proximity to the power feeder (cable).

D. Extraneous conductive parts including steel frames, battery racks, day-tank, pumps and piping are to be connected by insulated copper earthing conductors to main earth bar in compliance with bonding regulations.

MECHANICAL PLANT ROOMS AND FIXED MACHINERY

A. Frames and other conductive parts of all electrically operated equipment shall be connected to earth via an earthing conductor run with power feeder (cable) and connected at the supply end to the earth bar of the feeding panel which in turn should also be connected to the earth bar of the upstream feeding panel until eventually connected to the transformer/generator neutral which is earthed via earth electrodes. Earthing conductors of electrically operated mechanical equipment shall be sized to carry the maximum prospective ground fault current for at least 1 second.

(Earthing conductor size shall be indicated on design single line diagrams).

B. Main earthing bar or loop is to be connected at 2 extremely separate points to earth bar of the main electrical panel in the Mechanical Room directly through 2 test joints by insulated earthing conductors. This main earth bar shall only be used to earth purely mechanical equipment and other extraneous metal works in the mechanical room.

C. 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 Center (MCC), Motor Control Panel (MCP) or distribution unit.

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EARTHING OF CABLE TRAYS, RACEWAYS and CONDUIT

A. All Medium and Low Voltage feeders and branch circuits shall be grounded using supplemental grounding conductors.

Raceways will not be the sole source of grounding for feeders and branch circuits.

B. All ground wires installed in raceways other than tray, will be insulated.

C. Tray installations may use bare or insulated conductors.

D. The conductor will have green, green with yellow stripe insulation or a black insulation with green tape wrapped on all exposed surfaces in junction and pull boxes and termination points.

E. The ground wire will be appropriately bonded at each end of the raceway.

F. When voltage drop considerations require larger feeder or branch circuit conductors, the grounding conductor shall also be increased in size.

G. All raceways must be made electrically continuous from the point of origin to the termination point. Raceways include conduit, cable tray, cable bus, wiring trough or wire-way.

H. For new feeder installations that may be increased in ampacity by adding an additional parallel conductor in the future, the ground wire shall be sized for the ultimate circuit ampacity during the initial installation.

I. All cable trays will be installed with a grounding conductor. The conductor shall be bonded too each section of the tray using an approved connector or clamp. It is preferred that the grounding conductor run on the exterior of the tray.

Where conduit extends from the tray with branch or feeder wiring, the conduit and supplementary ground conductor will be bonded to the grounding conductor installed in the tray using compression devices to assure a continuous ground return path. The metallic sheath and armor of multi-core cables shall be bonded together and earthed.

J. Cable tray earthing conductors shall be bare or insulated copper conductor. The cable tray earthing conductor shall be sized to equal the earthing conductor associated with the biggest feeder cable installed inside the tray, with a maximum size of 95mm2 and a minimum size of 16mm2.

K. The cable tray earthing conductor will run the whole length of the cable tray and shall be finally terminated (or connected intermediately) to the earth bar associated with the highest rated switchboard or panel board from which cables are laid on this respective run of cable tray.

EARTHING AND BONDING MULTICORE CABLES

A. The metallic sheath and armor of multi-core 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.

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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.

INSTALLATION

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

B. Earth Rods: While sitting 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.

C. 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 strata of rock, and 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.

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

E. 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. The use of metallic conduit is strictly prohibited.

F. 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. Separate protective conductors which are not part of a cable have to be installed as close as possible (as is practicable) to the associated circuit conductors. Under no circumstances shall this separation be allowed to be greater than 200mm.

G. 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.

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

I. 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.

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.

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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.

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.

GRADING AND PLANTING

A. Restore surface features, including vegetation, at areas disturbed by Work of this Section. Re-establish 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 the original "Landscaping" requirements of the site. Maintain restored surfaces. Restore disturbed paving as indicated.

End of Specification