earthing system 26 05 26.pdf

Main Works Contract Project No. DU1222 Electrical Specifications Lotus Towers- Business Bay, Dubai

PART

PART

PART

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SECTION 26 05 26

EARTHING SYSTEM (UNDER MAIN CONTRACTOR'S SCOPE OF WORK)

1 GENERAL

1.1 General Instructions

1.2 Scope

1.3 Codes and Standards

2 PRODUCTS

2.1 Materials

2.2 Protective Conductors

2.3 Earthing Pit


3 EXECUTION

3.1 Earthing Installation

3.2 System Earthing

3.3 Service Equipment Earthing

3.4 Equipment Earthing of the Electrical Works

3.5 Structural Steelwork Bonding

Khatib & Alami (CEC) Section 26 05 26 Earthing System

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SECTION 26 05 26

EARTHING SYSTEM (UNDER MAIN CONTRACTOR'S SCOPE OF WORK)

PART 1 GENERAL

1.1 General Instructions

1.1.1 Works under this section shall be governed by Conditions of Contract and Section of Division 1.

1.2 Scope

1.2.1 Provide earthing system(s) for all Buildings as indicated on Electrical drawings, schedules and specified herein.

1.3 Codes and Standards

1.3.1 The Earthing system shall be in full compliance with the requirements of the lEE Wiring Regulations, Local Authorities Practices and the Specifications.

1.3.2 Any modification required by Local authorities shall be done at no extra cost.

1.3.3 The impedance of equipment (earth loop) shall comply the requirements of lEE wiring regulation.

1.3.4 The earthing resistance shall be in accordance with BS 7430 and in compliance with requirements of Local Power Authorities.

1.3.5 All earthing and bonding installation and equipment, shall comply with the requirements of the BS 7671 and BS 7430.

1.3.6 Deleted.

1.3.7 All Equipment earthing of the Electrical Works through a removable link at the Main Distribution Switchboard connecting the main earthing bus to the neutral bus. If no main switchboard is included in the works, a peripheral earth bus shall be provided in the Meters Room to which all the equipment earthing shall be bonded. The earthing bus shall in turn be bonded to the Local Authorities Low Tension Pillar neutral.

PART 2 PRODUCTS

2.1 Materials

2.1.1 Unless otherwise specified all materials used for earthing shall be of copper or approved copper alloys, and shall be specially manufactured for the purpose.

2.1.2 The complete earthing system shall be electrically and mechanically continuous to provide an independent fault current return path to the earthing source.


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2.1.3 Bolted connections shall be of the multiple bolt type. Bolts, washers and stop nuts shall be of high copper alloy. Ferrous hardware wi ll not be accepted.

2.1 .4 The impedance of equipment (earth loop) at any point in the electrical wiring system shall be sufficiently low to limit the voltage to earth and to facil itate the operation of the circuit protective devices in the circuits. Otherwise earth leakage circuit breakers shall be used.

2.1.5 Locations where the electrode is above water table, in rock or where there is soil is chloride free. 5/8" or%" diameter copper-bonded steel rod, the copper shall be 99.9% pure electrolytic molecularly bonded onto a low carbon steel core to BS 970 with a high tensile strength of at least 600 N/mm2 , the copper th ickness shall at least 0.25 mm. the rod shall be complete with driving stud, high strength copper alloy connectors and screw in spike.

2.1 .6 Earthing systems for sub-stations shall be in accordance with BS 7430 and the Local Electricity Authority regulations.

2.1.7 The earth system shall be tested in accordance with BS 7430.


2.2.1 Earthing wires (protective conductors) are not shown on the Drawings. All circuits running in conduits or in flexible conduits shall have earthing insulated conductors of minimum sizes as follows:

Current carrying conductor s

(mm2) Earthing Wire

(protective conductor) SP

(mm2) s less than or equal to 16 s s greater than or equal to 16 But less than or equal to 35

16

S greater than 35 0.5 s

2.2.2 If more than one circuit is included in a conduit, one protective conductor per neutral or per three phase circuit with no neutral shall be provided.

2.3 Earthing Pit

2.3.1 The earthing rod shall be constructed from copper clad steel rod. Copper sheath shall be 99.9% pure electrolytic copper. The steel core shall be of carbon steel, with tensile strength min 97,000 psi yield strength at 0.2% offset 85,000 psi, proportional limit 57,000 psi, percent of elongation 13%. Rod shall be cold drawn.

2.3.2 Earth pits shall be installed at least 2 meters away from build ing fagade.


2.4.1 Protective conductors shall be supplied and installed to in accordance with BS 7671.

PART 3 EXECUTION

3.1 Earthing Installation

3.1.1 Two separate earthing installations shall be provided. One installation shall be the System earthing and the other shall be the Authorities Service Equipment Earthing.


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Main Works Contract Project No. DU 1222 Electrical Specifications Lotus Towers- Business Bay, Dubai

3.1.2 Where earthing terminals are brazed to equipment, the metal shall be thoroughly cleaned prior to brazing and the impaired surface repainted to prevent corrosion .

3.2 System Earthing

3.2.1 The System Earthing shall consist of earthing pits connected in parallel if practicable, or shall consist of 95 mm2 ring (counterpoise) buried under ground at a depth of 1 meter minimum around the periphery of the building or substation if the latter is a separate structure. The specified system shall be in accordance with the project layout and location as indicated on the drawings.

3.2.2 The main earth ing bus of the main switchboard(s) if any shall be connected to the system earth ing by a 95 mm2 bare copper cable via a 40 x 5 mm main earthing busbar fixed on the wall in an approved location.

3.3 Service Equipment Earthing

3.3.1 The service equipment earthing shall be a separate earthing installation consisting of earthing pits connected in parallel. These pits shall be at least 8 meters away from the system earthing if practicable otherwise the service equipment earthing shall be bonded to the system earthing and the combined resistance shall be less than 1 Ohm.

3.3.2 To th is installation will be connected: the ring main unit earthing bar, the transformer(s) and HT switchgears, HT cable sheaths, all exposed structural metal works including metal cable trays when the substation is situated above a basement.

3.3.3 Connection material and sizes shall be as approved by the Local Authorities.

3.4 Equipment Earthing of the Electrical Works

3.4.1 Equipment earthing of the Electrical Works shall consist of bonding all non-current carrying metal parts of the Electrical installation to the System earth (TN-S system as per I EE Wiring Regulations, latest edition).

3.4.2 Non-current carrying metal parts of the electrical installation shall include such items as cabinets, exposed metal parts of apparatus as well as enclosures, doors, grill, etc., protecting or shielding electrical equipment from direct access to unauthorized personnel.

3.4.3 The series earthing of one piece of equipment to another will not be permitted. equipment earthing connections shall be tapped from the applicable earth source.

All

3.4.4 The cable armouring will not be accepted as equipment earth ing conductor.

3.4.5 All socket outlets, power apparatus, lighting fixtures and switches shall be earthed.

3.4.6 No point on the neutral shall be connected to the earth system except as described under "System Earthing".

3.4.7 Additional earthing pits may be shown on the drawings at different locations. These pits shall be bonded to the earthing bus of the relevant switchboards or panelboards as applicable in order to reduce the earthing resistance. Neutral at such points shall not be bonded to the earthing system.

3.4.8 Shells of all water heaters corresponding circuit.

shall be connected to the neutral and earthing of the

3.4.9 Bonding connections to gas and water pipes as required by the BS 7671 shall be made as near as practicable to the point of entry. These connections shall be made with solid


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3.4.10

3.4.11

3.5

3.5.1

3.5.1 .1

3.5.1.2

3.5.1.3

3.5.1.4

3.5.1.5

3.5.1.6

copper conductors of minimum cross section in accordance with BS 7671. These bonds shall be installed as inconspicuously and nearly as possible. The connections shall be visible after installation.

Bonding conductors shall comply with BS 7671.

Tests of individual and combined LV system earthing electrodes shall be carried out and the results recorded for presentation in accordance with BS 7671.

Structural Steelwork Bonding

Steelwork bonding shall be installed utilizing bolted or (thermic process) welded connections. Close coordination shall be made with other trades to ensure the timely installation of bonding conductors during the construction program. Bonding of structural steelwork shall be carried out in accordance with the BS 7671 and shall include but not be limited to the following examples:

Exposed Main Structural Columns & Beams.

Metallic Louvres and Grilles.

Crane Runway Beams

Steel Door and Frames

Reinforcing Steelwork Bars and Mesh

Mechanical and HVAC Plant

End of Section 26 05 26.


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Khatib Alami CEC_186: Section 26 05 26: Khatib Alami CEC_187: Section 26 05 26_2: Current carrying conductor s mm2: s less than or equal to 16: 16: S greater than 35: Khatib Alami CEC_188: Section 26 05 26_3: near as practicable to the point of entry These connections shall be made with solid: Khatib Alami CEC_189: Section 26 05 26_4:

earthing system 26 05 26.pdf

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