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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
2.4 Protective Conductors
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
26 05 26- 1
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Main Works Contract Project No. DU1222 Electrical Specifications
Lotus Towers- Business Bay, Dubai
**
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.
Khatib & Alami (CEC) Section 26 05 26 Earthing System
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Main Works Contract Project No. DU1222 Electrical Specifications
Lotus Towers- Business Bay, Dubai
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 Protective Conductors
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 Protective Conductors
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.
Khatib & Alami (CEC) Section 26 05 26 Earthing System
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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
Khatib & Alami (CEC) Section 26 05 26 Earthing System
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Main Works Contract Project No. DU1222 Electrical Specifications
Lotus Towers- Business Bay, Dubai
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.
Khatib & Alami (CEC) Section 26 05 26 Earthing System
26 05 26-5
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: