3.10 EARTHING SYSTEM
PART 1 GENERAL
3.10.1.1 DESCRIPTION OF WORK:
Work comprises complete installations to earth every source of energy protective earthing and bonding based on the TN-S system arrangement including:
- Transformer neutral earthing
- Main earthing terminals or bars
- Exposed conductive parts of electrical equipment
- Extraneous conductive parts
- Standby generator neutral earthing.
- Exposed conductive parts of mechanical equipment
3.10.1.2 REGULATIONS AND STANDARDS:
Carry out work in accordance with the following:
- IEC publications 364-3 and 364-4-41 - Electrical Installations in Buildings
- Latest edition of IEE Regulations for Electrical installations in Buildings - London
3.10.1. 3 DEFINITIONS OF TERMS:
-EARTH is the conductive mass of the Earth whose electric potential at any point is conventionally taken as zero
- EARTH ELECTRODE is the conductor or group of conductors in initial contact with and providing an electrical connection to EARTH
- EXPOSED CONDUCTIVE PART is any part which can be readily touched and which is not a live part but which may become live under fault conditions
- EXTRANEOUS CONDUCTIVE PART is any conductive part not forming part of the electrical installation such as structural metal work 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
-PROTECTIVE CONDUCTOR is a conductor used for some protective measures against electric shock and intended for connecting together any of the following parts:
- Exposed conductive parts
- Extraneous conductive parts
- Earth electrode(s)
- The main earthing terminal or bar(s)
- The earthed point of the source(s)
3.10.1. 4 ELECTRICALLY INDEPENDENT EARTH ELECTRODES:
Are earth electrodes located at such a distance from one another that the maximum current likely to flow through one of them does not significantly affect the potential of the other(s)
3.10.1. 5 MAIN EARTHING TERMINAL OR BAR:
Is the terminal or bar provided for the connection of protective conductors including equipotential bonding and functional earthing conductors (if required) to the means of earthing (earth electrode)
3.10.1. 6 EQUIPOTENTIAL BONDING:
Is the electrical connection to put exposed and extraneous conductive parts at a substantially equal potential
3.10.1. 7 EARTHING CONDUCTOR:
Is a protective conductor connecting a main earthing terminal or bar of an installation to an earth electrode or to other means of earthing.
3.10.1. 8 EQUIPMENT DATA:
Prior to ordering any materials submit complete data including but not limited to manufacturer's catalogues for earth rods connecting clamps earthing conductors protective conductors bonding conductors connectors and any other accessories exothermic welding kits and tools etc. and samples of conductors as requested.
3.10.1. 9 SHOP AND CONSTRUCTION DRAWINGS:
Submit shop and construction drawings including but not limited to the following:
- Exact location of earth pits rods and details of installation and connections
- Exact routing of buried earthing conductors with indication of cross-section depth of laying and covering
- Cross sectional area of all earthing protective and bonding conductors
- 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.
3.10.1. 10 APPROVED MANUFACTURERS:
Obtain materials from one of the following:
BICC (England
LECTRO (Egypt
Furse (England
or other equal and approved.
PART .2 EARTHING SYSTEM (TYPE TN-S)
3.10.2.1 GENERAL REQUIREMENTS
COMPONENT PARTS:
Of the earthing system are to include the following:
- Earth electrode (rods tapes etc.)
- Main earthing terminals or bars
- Earthing conductors
- Protective conductors
- Equipotential bonding conductors
- Electrically independent earth electrodes for special systems
- Accessories and termination fittings bonding welding and other materials.
EARTH ELECTRODE:
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 5 ohms.
RING TYPE EARTH ELECTRODE:
Provide buried earthing conductor in a closed loop in the exterior wall foundations underneath the waterproofing to which all earthing conductors are to be connected. Connection flags of same material as the earthing conductor are to be laid out a positions of service entrance and main switchboard rooms terminating in bolt-type earth points (studs) for connection of main earth bars. Additional flags are to be provided for connection of reinforcing bar down conductors at earth points as specified under lightening protective system.
FUNCTIONAL EARTH ELECTRODE:
Is to be provided separately from other earth electrode(s) but interconnected to such other earth electrode(s) through a suitably rated (470V) spark gap. Functional earth electrodes are to be used for earthing electronic equipment (communication equipment digital processors computers etc.) as required under the particular specifications and recommendation of manufacturer.
MAIN EARTHING BAR:
Provide main earthing bar at each point of service entrance or main distribution room and as described in the Specification or shown on the Drawings to which all earthing conductors protective conductors and bonding conductors are to be connected. Provide two insulated main earthing conductors one at each end of the bar connected via testing joints with the earth electrode at two points. Conductor is to be sized to carry the maximum earth fault current of the system at point of application with final conductor temperature not exceeding 160 deg. C for at least 5 seconds. Main earthing conductors are to be a minimum of 70 mm2 or as otherwise specified.
TESTING JOINTS (TEST LINKS):
Provide in an accessible position a testing joint (test link) on each main earthing conductor between earthing terminal or bar and the earth electrode.
PROTECTIVE CONDUCTORS:
Are to be separate for each circuit. Where a protective conductor is common to several circuits the cross-sectional area of the protective conductor is to be the largest conductor size. Selection of sizes is to be in accordance with table 54F of IEE Regulations and the equivalent.
PROTECTIVE CONDUCTORS:
Are not to be formed by conduit trunking ducting and the like. Cable armour where armoured cable is specified and is of steel is to be used as a protective conductor.
CONTINUITY OF PROTECTIVE CONDUCTORS:
The 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 insulating materials.
EARTH FAULT LOOP IMPEDANCE:
Ensure for final circuits supplying socket outlet that the earth fault impedance at every socket outlet is such that disconnection of protective device on over current occurs within 0.4 seconds and for final circuits supplying only fixed equipment the earth fault loop impedance at every point of utilization is such that disconnection occurs within 5 seconds. Use appropriate tables and present same for approval by the Engineer (IEE Regulations).
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, cable armour to nearest earthing terminals by means of equipotential bonding conductors. Cross-section of protective bonding conductor is not to be less than half the size of the protective conductor connected to respective earthing terminal and minimum of 4 mm2.
MAIN EQUIPOTENTIAL BONDING:
Connect, by means of main equipotential bonding conductor, the main incoming and outgoing water pipes and any other metallic service pipes with the main earth terminal or bar. Bonding connections are to be made as short as practicable between the point of entry/exit of those services and the main earthing bar. Where meters are installed bonding is to be made on the premises side of the meter. Cross-sections of conductors are not to be less than half the cross section of the earthing conductor connected thereto, and a minimum of 6 mm2.
IDENTIFICATION:
Label the connection of every earthing conductor to an earthing electrode and every bonding conductor to extraneous conducting parts in accordance with the Regulations as follows:
"SAFETY ELECTRICAL CONNECTION - DO NOT REMOVE".
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.
IDENTIFICATION:
Source earthing conductor (or neutral earthing conductor) is to be identified by continuous grey insulation along its entire length labeled 'neutral earthing'.
3.10. 2.2 UNIT TRANSFORMER SUBSTATION EARTHING
Main earthing bar is to be connected with earth electrode at its two extreme ends by means of two insulated earthing conductors through testing joints. Conductor size is to be a minimum of 120 mm2.
TRANSFORMER:
Earthing terminal is to be connected with LV main earthing bar by means of bare copper earthing conductor of not less than 20 mm2 per 100 kVA of transformer size and a minimum of 35 mm2.
TRANSFORMER NEUTRAL (STAR POINT) :
Is to be connected by means of insulated earthing conductor with low voltage side main earthing bar. A disconnecting device (bolted and tamper-proof) is to be provided at the transformer. Neutral earthing conductor is to be sized for maximum earth fault current of 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 a minimum of 50 mm2.
EARTH ELECTRODE:
Of substations is to comprise earth rods providing the connection point of an earthing conductor interconnected together and with the Earth Ring.
3.10. 2.3 EARTHING OF MAIN DISTRIBUTION BOARD PANELBOARDS
LIGHTING INSTALLATIONS AND WIRING ACCESSORIES
MAIN EARTHING BAR:
Provide main earthing bar in main distribution room(s) and connect to earth electrode by two insulated conductors (minimum 120 mm2) via testing joints.
EARTHING BARS OF MAIN DISTRIBUTION BOARDS:
Are to be connected by means of bare earthing conductor directly with main earthing bar at main distribution room and by protective conductor run with incoming feeder from respective supply point.
DISTRIBUTION LIGHTING AND POWER PANEL BOARDS:
Are to be connected by means of protective conductors run together with the incoming feeder cable, connecting earth terminals in panel boards with the respective main distribution board earthing bar.
SOCKET OUTLETS:
Are to be earthed by protective conductor looped around with the branch circuit and connected to an earth terminal within the socket outlet box and to which the socket outlet terminal is to be connected.
FINAL RING SUBCIRCUITS:
Protective conductor of every final ring sub circuit is to be in the form of a ring having both ends connected to the earth terminal at the origin of the circuit in the panel board.
LIGHTING FIXTURES AND OTHER EXPOSED CONDUCTIVE PARTS:
Of electrical installations such as switches heaters air conditioning units etc. are to be connected by means of protective earth conductors to earthing terminals of respective panel boards.
3.10. 2.4 GENERATOR PLANT EARTHING
GENERATOR NEUTRAL (STAR POINT):
Is to be connected by insulated earthing conductor through the neutral earthing device to main 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 deg. C but not less than of 50 mm2.
GENERATOR EARTHING TERMINAL:
Is to be connected with main earthing bar by means of bare copper conductor of cross section not less than of 35 mm2.
SWITCHGEAR (ATS) AND CONTROL GEAR:
Earthing terminals or bars of switchgear and control gear are to be connected by means of separate protective conductors with respective normal and emergency main distribution board earth bars.
EXTRANEOUS CONDUCTIVE PARTS:
Including steel frames battery racks, day-tank, pumps and piping are to be connected by means of bare copper earthing conductors to main earth bar in compliance with bonding regulations.
3.10.2.5 MECHANICAL PLANT ROOMS AND FIXED MACHINERY PROVIDE AND LOCATE:
Conviently in mechanical plant rooms, main earthing bar or loop and connect by means of earthing conductors with exposed conductive parts of motor control centre at its earthing bar and motors switches other electrical equipment etc. at their earthing terminals using 20 mm x 2 mm bare copper strips or 35 mm2 bare copper conductor (as a minimum size) or as necessary to carry maximum earth fault current for 1 second with final conductor temperature not exceeding 200 deg. C. Such conductors are to be securely fixed recessed in floor grooves or niches or fixed to walls by appropriate staples.
CONNECT:
Main earthing bar or loop at two extremely separate points, to earth electrode, directly through two test joints by means of insulated earthing conductors or connect to main earth bar by protective conductors.
FIX:
Earth bar or loop securely to building wall with copper or brass saddles.
MOTOR:
And other equipment earth terminals are to be connected also by the protective earth conductors of each branch circuit with the earth terminal/bar at the motor control center, panel or distribution unit.
3.10. 2.6 MATERIALS AND PRODUCTS
EARTH ROD:
Is to be copper clad steel 1.4 mm diameter 2.5 m length extendible as necessary to obtain the required earth resistance. Earth rod is to be complete with couplings head and bolted connector of sufficient size and number of bolted clamps to connect all cables terminated thereto.
BURIED EARTH CONDUCTORS:
Are to consist of bare annealed copper strip conductors 25mm x 2.5 mm or annealed stranded copper conductors of 70 mm2 cross-section.
EARTH PIT:
To be of precast, square or circular section concrete hand hole (minimum 450 mm internal diameter) provided with concrete cover and extending to about 150 mm below top of earth rod. An earth pit is to be provided for each earth rod where connection of an earth rod to an earthing conductor is to be carried out. Cover is to have an inset brass plate with inscription 'Earth pit - Do not remove'.
EARTHING CONDUCTORS:
Are to consist of insulated or bare copper conductor as described under respective application.
TESTING JOINTS (TEST LINKS):
Are to be copper or copper alloy with bolted end connections disconnectable by means of a tool and suitably sized for earthing conductors or earth bar connection. Links are to be fixed to porcelain or other approved insulating supports. Contact surfaces are to be tinned.
PROTECTIVE CONDUCTORS:
Are to be single core stranded annealed copper PVC insulated cables, having a rated insulation grade compatible with circuit protected or be a conductor forming part of a multi-core cable, color coded.
EARTHING ACCESSORIES:
Are to be of copper or copper alloy purpose made approved design compatible with points of connection and of adequate cross-section and current carrying capacity. Connectors and clamps are to be bolted type. Bolts nuts and washers are to be high quality phosphor bronze or copper silicon alloys.
PART 3 INSTALLATION AND FIELD WORK
3.10.3.1 INSTALLATION
CONTINUITY:
Ensure that complete earthing system is electrically continuous and mechanically secure.
EARTH RODS:
Ensure while sitting earth rods that resistance areas associated with individual rods do not overlap. Earth rods are to be sited at a distance greater than 600 mm from the foundation of a building. Where rock is encountered a hole of sufficient size is to be drilled before lowering the rod. Suitable surround of conductive filler such as Marconite or Bentonite are to be provided around the rod or equal filler that will not corrode the rod.
BURIED EARTHING CONDUCTORS:
Are to be laid at a depth as shown in drawings.
EARTHING CONDUCTORS:
Are to follow the shortest path between earth electrode and main earthing terminals or bars.
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.
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 a secure bond.
PROTECTION AGAINST CORROSION:
Protect bolted connections against corrosion either by filling with Vaseline or coating with a special anti-corrosion compound and proper capping.
CONNECTIONS:
Earth connections are to be readily accessible. If inaccessible earth connection is permitted approved exothermic welding or brazing technique is to be employed.
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.
3.10.3.2 TESTS ON SITE AND RECORDS
RESISTANCE:
Of earth electrode is to be measured during dry season and checked against specified resistance using an approved test method such as described in the IEE regulations Appendix 15.
ELECTRICAL CONTINUITY:
Of all earthing and protective conductors including main and supplementary equipotential bonding conductors is to be checked.
EARTH FAULT LOOP IMPEDANCE:
Of all circuits is to be measured and checked against calculated impedance figures.
OPERATION:
Of residual current protective devices is to be checked.
RECORDS:
Submit the following:
- Scaled drawings as-installed showing the actual layout and specification of all components of the earthing system
- Nature of soil and any special earth arrangements etc.
- Date and particulars of soil conditioning method and agents if used.
- Test conditions and results obtained.
- Calculation sheets.
LIGHTNING AND OVERVOLTAGE PROTECTION SYSTEM
PART 1 GENERAL
1.1 SCOPE: This section covers the furnishing and installation of lightning and overvoltage protection system of the project, complete for the indicated GRE Office Building
1.2 APPLICABLE PUBLICATIONS: The following publications of the issues listed below, but referred to thereafter by basic designation only, form a part of this Specification to the extent indicated by the reference thereto:
1.2.1 German Standards:
DIN 4801 Lightning Protection Manufacturing Standard.
DIN/VDE 0110 Part 1 Overvoltage Protection.
1.2.2 CEI/IEC Standards:
1024-1 Planning and Installation of Lightning Protection.
1.2.3 British Standards:
BS CP1013 Earthing
BS 6651 Protection of Structures Against Lightning.
1.2.4 Underwriter's Laboratories, Inc. (UL) Publications.
UL 467 Grounding and Bonding Equipment.
1.2.5 National Fire Protection Association (NFPA).
NFPA 780-1996 Lightning Protection Code.
1.3 Drawings: Indicate the extent and general arrangement of the lightning protection system. If any departures from the Drawings are deemed necessary by the Contractor, details of such departures and reasons therefore shall be submitted as soon as practicable to the Client Representative for approval. No such departures shall be made without the prior written approval of the Client Representative. Lightning protection systems for applications other than those specified herein shall conform to the NFPA Code No. 781 and BS 6651 and/or VDE/DIN 4801.
1.4 SUBMITTALS:
1.4.1 Shop Drawings: Shop drawings shall be submitted in accordance with Section 16010: Electrical General Requirements, and shall consist of a complete list of materials, including manufacturer's descriptive and technical literature, catalog cuts, drawings, and installation instructions. Shop drawings shall also contain details to demonstrate that the system has been coordinated and will function as a unit. Drawing shall show proposed layout and mounting and relationship to other parts of the work. In the event any items of material or equipment contained in the drawings and list of materials fail to comply with the Specifications, such system, items or the complete work will be rejected.
1.4.2 Proof of Compliance: Where materials or equipment are specified to comply with requirements of UL and BS, proof of such compliance shall be submitted. The label of or listing in the UL Electrical Construction Material Directory will be acceptable evidence. In lieu of the label or listing, a written certificate may be submitted from an approved nationally recognized testing organization equipped to perform such services, stating that the items have been tested and conform to the requirements and testing methods of Underwriter’s Laboratories, Inc. and British and/or Quality Assurance Standard.
PART 2 PRODUCTS
2.1 GENERAL REQUIREMENTS: No combination of materials shall be used that form an electrolytic couple of such nature that corrosion is a accelerated in the presence of moisture unless moisture is permanently excluded from the junction of such materials. Where usual conditions exist which would cause corrosion of conductors, conductors with protective coatings or oversize conductors shall be used. Where a mechanical hazard is involved, the conductor size shall be increased to compensate for the hazard of the conductors.
AIR TERMINALS AND FIXINGS: Terminals shall be in accordance with UL, BS and NFPA No. 780. Minimum size shall be 15mm diameter x 1000mm long made of molecularly bonding of 90-99% pure electrolytic copper no to a low carbon steel.
2.2 GROUND RODS: Rods shall conform to UL 467 and shall be made of copper-clad steel minimum size of 20mm diameter x 3000mm long.
2.3 BOND PLATES: UL 96, Class or as applicable.
2.4 Provide ground electrode assembly (ground/concrete pit as indicated) at the ground rod locations. Pit shall be as indicated and shall have a 10mm thick cast iron cover installed at grade level. Wells shall have low resistance and conductor connections shall be clamped or exothermically welded to the ground rod as necessary.
PART 3 EXECUTION:
3.1 GENERAL REQUIREMENTS: The lightning protection system, except as specified herein, shall consist of air terminals, roof conductors, down conductors, ground connections, and ground electrically interconnected to form the shortest distance to ground without passing through any non-conducting parts of the structures.
All conductors on the structures shall be exposed where conductors are in protective sleeves and exposed on the outside walls. Secondary conductors shall interconnect with ground metallic parts within the building.
3.2 ROOF CONDUCTORS: Roof conductors shall be connected directly to the roof parapet or ridge roll. Sharp bends or turns in conductors shall be avoided. Necessary turn shall have a radius of not less than 203mm. Conductors shall preserve a downward or horizontal course and shall be rigidly fastened every 1.2 meters along the roof and down the building using the structural rebars and to the ground. Metal ventilators shall be rigidly connected to the roof conductor at three places. All connections shall be electrically continuous. Roof conductors shall be coursed along the continuous part flat roof, ridges, parapets and edges, and where necessary, over flat surfaces, in such a way as to join each air terminal to all the rest. Roof conductors shall be connected to form a closed loop where possible.
3.3 INTERCONNECTION OF METALLIC PARTS: Metal doors, windows and gutters shall be connected directly to the grounds using not smaller than 25mm2 copper conductor, or equivalent. Conductors placed where there is probability of unusual wear, mechanical injury, or corrosion shall be greater electrical capacity than would normally be used, or shall be protected. The ground connection on metal doors and windows shall be by means of mechanical ties under pressure, or equivalent.
3.4 GROUND CONNECTIONS: Ground connections comprising continuation of columns from the structure to the grounding electrodes shall securely connect the column and ground in a manner to ensure electrical continuity between the two. All connections shall be of the
exothermic type. There shall be a ground connection of each perimeter column. Metal water pipes and other large underground metallic objects shall be bonded together with all grounding mediums. Ground connections shall be protected from mechanical injury. In making ground connections, advantage shall be taken of all permanently moist places where practicable, although such places shall be avoided if the area is wet with waste paper that contains chemical substances.
3.5 GROUND ELECTRODES: A ground electrode shall be provided as shown and indicated on the drawings. A driven ground shall extend into the ground for a distance of not less than 3.05 meters. Ground rods shall be set not less than 0.60 meter, nor more than 2.5 meters, from the structure. The complete installation shall have a total resistance to ground of not less than 5 ohms or as required in other sections of the specifications..
3.6 STEEL FRAME BUILDING
3.7 INTERCONNECTION OF METAL BODIES: Metal bodies of conductance shall be protected if not within the zone of an air terminal. All metal bodies of conductance having an area 10 square meters or greater or a volume of 25 cubic meters or greater shall be bonded to the lightning protection system using main size conductors and bonding plate having a surface contact area less than 100mm square. Provisions shall be made to guard against the corrosive effect of bonding dissimilar metals. Metal bodies of inductance shall be bonded at their closest point to the lightning protection system using secondary bonding conductors and fittings. A metal body that exceeds 2 meter in dimensions, that is situated wholly within a building, and that does not at any point come within 1.80 meters of a lightning conductor or metal connected thereto shall be independently grounded.
3.8 INSPECTION: The lightning protection and overvoltage system will be inspected by the Client Representative to determine conformance with the requirements of this Specifications. No part of the system shall be concealed unless to authorized by the Client Representative. In addition, a certificate shall be furnished to the Client Representative indicating Underwriter’s Laboratories Inc. or British Standard, for approval of all lightning protection systems provided on the buildings.
3.9 SUPERVISION: The service of a qualified engineer or technician shall be provided to supervise the installation, and perform adjustments and tests to the equipment. The engineer or technician shall be qualified by experience and training in the installation and testing of lightning protection system. The engineer or technician shall instruct designated Client Personnel in the operation, adjustment and maintenance of the system.
3.10 MANUAL: Upon completion of the installation and prior to final inspection, the Contractor shall furnish four copies of a manual giving complete instructions, including wiring diagrams, drawings for the operation, inspection, testing and maintenance of the lightning and overvoltage protection system. Manual shall be both in English and Arabic languages where necessary or as required by the Client Representative.
END OF THIS SECTION
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