electrical works specifications (acmv)

AECOM Mechanical Works – Technical Specification MVAC/ELECT/1 Mechanical Ventilation and Air-conditioning Installation

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Section 12 – Electrical

1.0 General 1.1 This section covers the electrical equipment and services necessary for the efficient, safe and satisfactory

operation of the various systems detailed elsewhere in the Specification, including

a) All motors, starters, isolating switches and fuse switches for this Sub-Contract.

b) Local Control Panels (LCPs) complete with remote push buttons, selector switches, indicator lights, relays, electrical circuit breakers etc.

c) All electrical power panels – Switchboards, Motor Control Centres (MCCs), Local Control Panels (LCPs), and Distribution Bards – shall be type-tested to Form 3 of IEC 60439-1 complete with remote push buttons, selector switches, indicator lights, relays, MCCBs etc suitable for 400 Volt, 50 Hertz for three-phase loads and 230 Volt for single-phase loads with an operating ambient temperature of up to 40 C with 100% R.H. at maximum continuous rating without exceeding the maximum temperature permitted by the relevant British Standard or Singapore Standard. The Contractor shall guarantee all boards are constructed in accordance the type tested requirements of Singapore Standards SS 293 Form 3.

d) All control equipment, control wiring and associated conduit works.

e) Conduit, cable tray, cabling and control wiring between the Control Panels and all equipment and control elements, unless otherwise stated.

f) Cables between electrical isolators or electrical control boards and equipment or control elements. 2.0 Rules and Regulations 2.1 All electrical works, material and equipment shall comply with the following:

a) SS CP 5:1998 and Amendments (2008) - Code of Practice for Electrical Installations

b) SS CP 551:2009 - Code of Practice on Earthing c) SS 530: 2006 - Code of Practice for Energy Efficiency Standard For Building Services And Equipment.

d) All relevant Singapore Standards or British Standards Specifications for Equipment

e) The Electricity Regulations (Public Utilities Act)

f) The Public Utilities (Electricity Supply) Regulations (Public Utilities Act)

g) The Public Utilities (license to use or operate Electrical or Supply Installation) Regulations (Public

Utilities Act)

h) The Electrical Works and Contractors Licensing Regulations i) Any other Rules and Regulations in operation


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2.2 All electrical installation shall be certified by the Sub-Contractor’s Licensed Electrical Worker (LEW) and the power supply diagram shall be endorsed by the Sub-Contractor’s LEW.

3.0 Power Supply

3.1 The power supply shall be 400 Volts, three-phase, 50 Hertz and 230 Volts single-phase, 50 Hertz. 3.2 The wire system shall comprise of live, neutral and CPC (Circuit Protection Conductor) terminated into suitable

isolators (by others unless specified otherwise) as shown on the Drawings. The 3.3 Contractor shall provide all subsequent power and control wiring as well as the main control panel and sub-panels

for each system. Layout drawings shall be submitted for approval before fabrication.

3.4 Generally, cabling shall be XLPE insulated cables run in galvanised steel electrical conduits or trunking, except for:

a) services essential to fire safety, these shall be Fire Rated type, b) services subject to external mechanical damages, these shall be Armoured type; c) services installed over confined spaces, these shall be Low Smoke Zero-Halogen;

These shall be according to single line drawing and other sections of this Specification. 3.5 The wiring for all safety cut-out controls shall be incorporated with the compressor starter as mentioned above. All

automatic temperature controls shall be energised via which relays operate when the respective fan or other motor starts. The circuit indicator lights shall be taken from the out going side of the respective starters.

3.6 The Contractor shall ensure that the running power factor for all motors shall not be less than 0.85 for those under

14.7kW and 0.9 for those it. Power Factor correction may be provided if necessary, subject to the approval of the S.O.

4.0 Drawings 4.1 The Contractor shall submit detailed construction drawings of all switchboards and power supply layout for the

approval of the S.O. before construction commences. 4.2 Such drawings shall show construction details and shall incorporate a full list of proposed materials, equipment,

meters and accessories to be used, and the method of supporting equipment and busbars. 5.0 Standards 5.1 The equipment and materials used and the method of construction as applicable shall conform to the following

British Standard (B.S.) or International Electrotechnical Commission (I.E.C.) or National Electrical Manufacturers Association (NEMA) standard. a) Busbars and Busbar connection, arrangements and markings, and grade of copper - B.S. 158, 159,

1433 and 1977.

b) Heavy duty air circuit breakers for A.C. system - B.S. 4752.

c) Moulded case circuit breakers - B.S. 3871 Part 2

d) Indicating Instruments - B.S. 89 1st Grade.


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e) Integrating meters - B.S. 37 Parts 1 and 2.

f) Integrating meters with cyclometer registers - B.S. 37 Part 4.

g) Protection relays - B.S. 142. h) Fuses - B.S. 88.

i) Contactors - B.S. 775 or IEC 158.

6.0 Local Authorities Requirements 6.1 All electrical works, installations and materials supplied shall comply strictly to the requirements and standard of the

following local Authorities: a) Public Utilities Board, Singapore

b) Code of Practice for Fire Precautions in Buildings 2013, SCDF, Singapore

c) The Factory Inspectorate (Ministry of Manpower)

d) The latest edition of SS CP 5:1996 (Code of Practice for wiring of electrical equipment of buildings)

including CP5 Amendments No.1: 2008

e) SS 530: 2006 - Code of Practice for Energy Efficiency Standard For Building Services And Equipment.

f) The latest edition of SS 551: 2009 - Code of Practice on earthing 7.0 Electrical Earthing The power supply shall be 400 Volts, three-phase, 50 Hertz and 230 Volts single-phase, 50 Hertz. 7.1 General

a) The metal parts of all switch gears, metal conductors and all metal work liable to become alive in the event of failure of insulation and the earth connection of all electrical fittings and appliances shall be effectively earthed by means of earth continuity conductor of adequate size. The entire earthing installation shall fully comply with all relevant clauses of the latest edition of Singapore Standard CP5 and latest edition of SS 551.

b) The earth continuity conductor shall be of high -conductivity copper continuous throughout its length and approval must be made known to the S.O. prior to any jointing by mechanical clamps.

7.2 Earth Connections

Earth continuity conductors from all exposed metal parts of equipment required to be earthed including earth connections to plug sockets shall be connected by one of the following appropriate methods:

To earth connection at the distribution board supplying the equipment of plug socket.

To any point on the sub-main or main earth continuity conductor supplying the relevant distribution board.


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To earth leakage circuit breaker installed in accordance with PUB's requirement.

The Contractor shall ensure that there is earth continuity in all trunkings, pipes, ducts, etc. Earth links of minimum size of 6 mm², in the form of flexible cables, shall be used to ensure continuity.

The end of earthing lead shall be labelled with 4.75 mm lettering "SAFETY ELECTRICAL EARTH DO NOT REMOVE" stamped onto an aluminium plate.

7.3 Size and Type of Copper Earth Conductor

The size of copper earth conductor shall be conformed to Singapore Standard CP 5 latest version. But, the minimum size of 6 mm² green/yellow PVC insulated copper cable shall be used.

Each earth conductor shall be clearly labelled.

8.0 Motor Control Centre/Local Control Panels 8.1 The Contractor shall supply, deliver, install, test and commission Motor Control Centres (MCC), Local Control

Panels (LCP) of a type specified hereafter complete with suitable doors that allow easy access to all components installed therein.

8.2 All components shall be so arranged as to facilitate inspection and maintenance. 8.3 Surface mounted circuit breaker shall be supplied to control all components together with associated starter

contactor etc. mounted on the panel inside the cubicle. Associated components shall be grouped. Flush mounted push button and neon pilot light shall be fitted on the front fascia of the cubicle.

8.4 Appropriate relays shall be incorporated to protect all 3-phase motors from overload, undervoltage, single-

phasing and wrong sequence of connection.

8.5 All single phase motors shall be protected by thermal overload of a type with a tripping current adjustable in steps of 0.1 amperes.

8.6 All MCCs and LCPs shall be provided with a separate interfacing compartment containing the terminal strips for

connections to the Building Automation System. 8.7 All MCCs and LCPs shall be provided with voltage free contacts and all necessary relays (including 4 spare

contacts) for remote indication and control by the BMS. 8.8 All breakers to be used for the starting/running of motors shall be motor load protection type. 9.0 Local Control Board (LCP)/Starters Panels 9.1 The MCC shall be designed, fabricated, assembled and tested in accordance with the requirements, standards

and specifications. 9.2 All cabinets of the control/starter panels shall be of metal clad front type and manufactured from minimum 2.0

mm (14 SWG) gauge hot dipped galvanised sheet steel using folded sections or angle iron bracing for rigidity of construction. Floor mounted control panel shall be of metal clad flush fronted, totally enclosed cubicle type of similar construction as wall mounted type.


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9.3 The LCP with main incoming circuit protectors rated below 100 Amp Trip shall be of the wall mounting type, and shall employ power distribution panel boards for branch circuits together with starters, protective devices and indicating instruments.

9.4 The cabinet shall be adequately ventilated and be dust, drip and vermin proof. Unless specified otherwise, the degree of protection of the enclosure shall be IP 44 in accordance with IEC Publication 144.

9.5 The construction shall be such that it allows for ready access to the interior of the cubicles for operation and maintenance purposes.

9.6 Where they are installed exposed to weather and at areas of high humidity, they shall be of weatherproof

construction to the approval of the S.O. 9.7 All cubicles and panels shall wherever practicable be of standard pattern and dimensions.

9.8 All steel work for the cubicles and panels shall be new and free from rust and scale. The finish shall be baked

enamel of colour to S.O. for approval. 9.9 All fixings, screw, bolts and nuts, latches and locks shall be cadmium-plated and chromed. 9.10 All cubicles and panels shall have hinged doors (concealed hinge type). Rubber gaskets shall be provided

between all doors, covers and cubicles. 9.11 Switches and isolators supplied shall be of the totally enclosed, heavy duty, air break and quick action type with

a short circuit capacity suitable for the rating of the equipment to be connected. Positive indication of switch position shall be given by a mechanical "on" or "off" device.

9.12 Interface barrier shall be provided for the fuse cartridges compartment to safeguard flashover. 9.13 All fuses shall be HRC Cartridge type, having fusing factor of less than 1.5 and complying with BS 88 Class Q1. 9.14 Instruments, indicating lights, rotary switches, etc. shall be mounted directly on a fixed fascia panel suitably

stiffened to hold such items firmly under all conditions or operation. 9.15 The LCP shall be provided with all wiring and accessories for the indicating and controlling devices in the

supervisory control and equipment status panel. 9.16 The LCP centres shall comprise of but not limited to the following components and accessories:

Main Incoming Circuit Breaker with protective, indicating and metering devices. Branch circuit protectors with safety devices indicating and metering instruments.

Motor contactors (starters) of types and capacities as specified complete with protective and safety

devices, instrumentation and control accessories. A separate compartment to housed the DDC sub-station and all interfacing cabling connectors.

All interlocking relays for fire protection control.

9.17 No-volt release shall be of the manual reset type such that on restoration of the supply, the motor cannot restart

automatically. 9.18 Overload relays shall be factory calibrated and sealed with integral heaters. They shall be incorporated with

stop switch/manual reset control. The range for setting of overload shall be suitably selected for the equipment to be connected. They shall be of approved type and manufacture.


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9.19 Indicating lights shall be provided for all starter and control panel to indicate power incoming mains available, mains turned on, motor run and stop status, motor overload trip, alarm, etc. Indicating lamps used shall be of heavy duty type and shall be submitted for approval prior to order. Lamp provided shall be of long life type with a minimum guaranteed lift of 10,000 hours continuous operation.

9.20 Push buttons shall be provided for manual starting and stopping on all starter panels. All push buttons shall be designed for switching of control circuits up to 500 V AC and shall be of heavy duty type and approved manufacture.

9.21 Contactors shall be double break non-stick and chatter-free and of approved manufacture. Thermal protection

and no-volt release shall be provided for each contactor. Contactors shall satisfactorily close at a minimum of 80% nominal volts.

9.22 Small wirings shall comply with BS 6346 of 600/1000 V grade and PVC insulated. They shall be neatly cleated

and bunched accordingly to their function that easy identification can be maintained.

9.23 The branch circuit protectors and the main circuit protectors shall be moulded case circuit breakers of reputed manufacture, and shall have adequate current carrying capacities.

9.24 Moulded Case Circuit Breakers shall comply with BS 871 : Part 2. The current ratings, frame sizes and

minimum interrupting capacities of the MCCB shall be specified in the Drawings.

9.25 All moulded case current breakers shall have interrupting capacities in excess of 43 KA (symmetrical) or where the short circuit rating of the Motor Control is lower, the breaker interrupting capacity shall correspond to the short circuit rating of the LCP.

9.26 All relays and timers supplied shall be of make and type to the S.O.'s approval. 9.27 Ammeter shall be suitable for flush mounting and shall be square or rectangular type with moulded plastic

escutcheons. Range of Ammeter shall be suitable for the service intended.

9.28 All terminal blocks shall be of adequate rating and shall be of approved maker. Sufficient terminals shall be made available for easy terminations and in no case shall more than 2 cores be allowed to be terminated at any terminal.

9.29 All wiring shall be properly labelled and identified with approved type feruled numbers which shall correspond

exactly to the numbering system as shown in the wiring and connection drawings for the switchboards or starter panels. All terminals blocks shall also be similarly labelled for identification. All wire termination shall be done with approved type lugs.

9.30 Name-plates shall be provided for each circuit, equipment and instrument for identification and designation in

accordance with its function. Name-plates shall be of black plastic material with engraved white lettering and shall be fixed to the panel by brass screws.

9.31 All power cables shall be of copper conductors and phase conductors shall follow the acceptable colour code. 9.32 RCCB shall be provided in all control/starter panels below 100 Amps and earth leakage relay (with time delay)

and overcurrent relay shall be provided in panel/board 100 Amps and above. Earth fault protection of IDMTL type (earth leakage) and DTL type (overcurrent) shall be provided for multiple equipment panel/board.

9.33 Where earth fault protection is specified for motor branch circuits, earth fault relays shall be incorporated into

the motor starters. The fault level setting of these earth fault relays shall be field adjustable.


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9.34 The following indicating, measuring, controlling and alarming devices shall be incorporated into the LCP : One (1) ammeter 4½" (113 mm) and one (1) voltmeter 4½" (113 mm) dial with selector switches for the

indication of current and voltage between phases, and between each phase and neutral for the mains incoming power supply, together with indicating pilot lights.

One (1) rotary selector switch "BMS/REMOTE-OFF-LOCAL" operation of the motor or equipment.

One (1) ammeter with selector switch for measurement of line voltage and phase current for each motor on each starter panel. The selector switch shall be marked with "Blue-Red-Yellow" indicating the phases.

One (1) set start/stop push buttons colour coded for each motor on each starter panel.

One (1) set pilot lights for the indication of “RUN-STOP-TRIP” condition of each motor on each starter

panel.

One (1) pilot light, which shall mark "DIRTY", to indicate each bank of AHU filter's resistance status. The light shall come on when the filter's resistance reaches the specified level.

One (1) 20 ampere spare MCCB circuit breaker.

All necessary MCBs complete with outgoing cabling for auxiliary and associated equipment power supplies.

9.35 The "BMS/REMOTE-OFF-LOCAL" operations at the LCP shall be interpreted as follows:

"BMS/REMOTE" means the starting of motor or equipment can be started at the BMS console or at the

supervisory control panel through IMSS.

"OFF" means the complete power cut-off of motors.

"LOCAL" means the starting of motor or equipment shall be started at Local Control Board and it could not be started at the BMS console or the supervisory control panel of IMSS.

10.0 Motor Control Centres (MCCs)/ A/C Switchboard 10.1 The MCC shall be designed, fabricated, assembled and tested in accordance with the requirements, standards

and specifications.

10.2 The MCC shall be of the self-contained, floor mounting, extensible, metal clad, flush-fronted, front and rear access cubicle type, built up from completely enclosed units housing all the circuit breakers, meters, selector switches, indicating lamps and protection relays, current transformers, protection transformers, contactors, busbars, fuses, anti-condensation heaters complete with indicating lamps and switches, and etc.

10.3 Switches and isolators supplied shall be of the totally enclosed, heavy duty, air break and quick action type with

a short circuit capacity suitable for the rating of the equipment to be connected. Positive indication of switch position shall be given by a mechanical "on" or "off" device.

10.4 Interface barrier shall be provided for the fuse cartridges compartment to safeguard flashover. 10.5 All fuses shall be HRC Cartridge type, having fusing factor of less than 1.5 and complying with BS 88 Class Q1.


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10.6 Instruments, indicating lights, rotary switches, etc. shall be mounted directly on a fixed fascia panel suitably stiffened to hold such items firmly under all conditions or operation.

10.7 The MCC shall be provided with all wiring and accessories for the indicating and controlling devices in the

supervisory control and equipment status panel. 10.8 Motor control centres shall comprise of but not limited to the following components and accessories:

Main Incoming Circuit Breaker with protective, indicating and metering devices.

Main bus sections and vertical bus sections as applicable with full neutral bus and ground bus

sections.

Branch circuit protectors with safety devices, indicating and metering instruments.

Motor contactors (starters) of types and capacities as specified complete with protective and safety devices, instrumentation and control accessories.

10.9 The bus sections shall have adequate current carrying capacity and be of all copper and electro-tinned. The

bus sections shall be adequately protected and supported and shall have a short circuit rating not less than 43 KA (symmetrical) at 400 volts for 3 seconds.

10.10 The branch circuit protectors and the main circuit protectors or all motor control centres shall be moulded case circuit breakers (MCCB) of reputable manufacture, and shall have adequate current carrying capacities.

10.11 All moulded case current breakers shall have interrupting capacities in excess of 43 KA (symmetrical) or where

the short circuit rating of the Motor Control is lower, the breaker interrupting capacity shall correspond to the short circuit rating of the motor control centre.

10.12 RCCB shall be provided in all MCC of 100 Amps and below. Earth leakage relay (with time delay) and overcurrent relay shall be provided in MCC of 100 Amps and above. Earth fault protection of IDMTL type (earth leakage) and DTL type (overcurrent) shall be provided for multiple equipment panel/board.

10.13 MCCs with main incoming circuit protectors rated below 100 Amp Trip shall be of the wall mounting type, and shall employ power distribution panel boards for branch circuits together with starters, protective devices and indicating instruments.

10.14 Motor control centres with current or voltage operated earth leakage circuit breakers for protection of branch

circuits feeding motors or other air conditioning and mechanical ventilation equipment will not be accepted. However, where earth fault protection is specified for motor branch circuits earth fault relays shall be incorporated into the motor starters. The fault level setting of these earth fault relays shall be field adjustable.

10.15 The following indicating, measuring controlling and alarming devices shall be incorporated into the MCC: One (1) ammeter 4½" (113 mm) dial and one (1) voltmeter 4½" (113 mm) dial with selector switches

for the indication of current and voltage between phases, and between each phase and neutral for the mains incoming power supply, together with indicating pilot lights.

One (1) digital power meter to read the voltage, line current, power factor, power (kVA, kVAr, kW), and energy (kVA-hr, kVAr-hr, kW-hr)at the main incoming feeder and every circuit feeders. The meter shall be revenue collection class.

One (1) rotary selector switch "REMOTE-OFF-LOCAL" operation of the motor or equipment.


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One (1) ammeter only with selector switch for measurement of line voltage and phase current of each motor on each starter panel. The selector switch shall be marked with "Blue-Red-Yellow" indicating the phases.

One (1) set start/stop push buttons colour coded for each motor on each starter panel.

One (1) set pilot lights for the indication of "RUN-STOP-TRIP" condition of each motor on each starter panel.

One (1) set of rotary selector switch for pumps operation, on each of the condenser and chilled water

pumps starter panel.

20% spare space with MCCBs of 20% spare shall be provided for each main incomer feeder.

10.16 The "BMS/REMOTE-OFF-LOCAL" operations at the MCC shall be interpreted as follows: "BMS/REMOTE" means the starting of motor or equipment can be started at the BMS console or the

supervisory control panel through IMSS.

"OFF" means the complete power cut-off of motors.

"LOCAL" means the starting of motor or equipment shall be started at the Motor Control Centre and it could not be started at the BMS console or the supervisory control panel of IMSS.

11.0 MCC Tests 11.1 Delivery Test

After the equipment has been erected on site, and before final connection to supply, the Contractor shall at his own expenses : to arrange with the independent Licensed Electrical Tester to carry out the necessary testing and

commissioning. The test shall be witnessed and certified by the Electrical Installation Licensed Electrical Worker and result submitted to the S.O. as record.

to carry out all necessary adjustments and/or tests necessary to demonstrate that the equipment complies with the requirements of this Specification with his own equipment, in the presence of and to the satisfaction of the S.O. Such tests shall include:

Demonstration that all equipment are installed and all wiring connected, so that the board functions as required.

Tests of accuracy of all measuring instruments.

Insulation resistances between phases, between each phase and neutral, and between each

phase, neutral and earth with circuit breakers closed.

Insulation resistance across breaks in all circuit breakers, with the breaker open and with all equipment installed.

Power - frequency voltage tests, in accordance with clause 63 of B.S. 116.

Copies of test sheets, showing the results of all test carried out in accordance with this section of the Specification, shall be submitted in Triplicate, to the S.O.


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11.2 Routine Tests

The Contractor shall submit certified test sheets showing details of all routing tests applied, during manufacture, to the switchboards and the individual components thereof. Without in any way affecting the generality of this Clause such test shall include the following clauses relating to switchgear: Operating test, consisting of fifty operations of the operating mechanisms performed with the closing

device. Millivolt drop test, or resistance test at the rated current of the equipment across all contacts

individually, and as a complete unit as a check against temperature rise type test if applicable. The record taken on the type test shall be taken as datum if applicable.

Tests on each switching unit to determine the satisfactory operation of trip coil or coils at the minimum and the normal tripping voltage.

11.3 Type Tests

The switchboards, ie MCCs, shall be capable as a whole of withstanding without damage the electrical, mechanical and thermal stresses produced under short circuit conditions equivalent to the interrupting capacities of RMS Symmetrical Amperes at 400 Volts A.C. of the incoming breakers for 3 sec. and shall comply with all requirements of B.S. 162. In addition to details of type tests for making and breaking capacity, as required under this Clause of the Specification, the Contractor shall submit certified details of type tests for mechanical endurance and temperature rise from each type of switching equipment included in the Contract, such test to be carried out in accordance with the requirements of their relevant British Standard Specifications. Switchboard manufacturer shall be required to submit two (2) sets of detail switchboard construction drawings approved and endorsed by his principal to ensure the switchboards are constructed and manufactured according to the type test requirements and a letter of undertaking for each type tested switchboard. All parts of the MCC shall be subjected to type tests to verify compliance with the relevant BS standard. The type test shall include verification of temperature rise limit, dielectric properties, short circuit strength, continuity of protective circuit, clearance and creepage distances, mechanical operation and degree of protection. The Contractor shall submit type test certificates issued by independent testing authority which shall be a member of the Associated of Short Circuit Testing Authority (ASTA).

11.4 Frame Construction

MCC/Main switchboard frame shall be fabricated from not less than 12 B.G. (2.5 mm thick) steel sheet pressed or rolled to shape. All joints shall be neatly welded and finished flush with the adjacent surfaces by grinding and/or machining. No joints shall be located on a corner and all base edges shall be lipped. Structural members and bracing where necessary shall be welded or bolted to the frame. Each cubicle shall be of standard size, uniform in height, width and depth. Each cubicle shall be adequately ventilated and the interior of each cubicle shall be dust, insect and vermin proof. The Entire Construction and individual compartment and cubicle shall be rated IP42 for indoor application. For outdoor applications, IP54 enclosure shall be provided.

11.5 Doors and Panels


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Doors and instrument panels shall be constructed with not less than 12 SWG (2.5 mm thick) steel

sheet pressed or rolled so that edges are given a neat round finish and shall be reinforced with a suitable frame welded to the inside folded edge of the door. An approved stiffener shall be welded to the inside of each door and/or panel.

The side, back and top panels as well as the front panel shall be removable to provide access.

The doors and panels shall be seated on a neoprene gasket cemented to the frame. Doors shall hang

on substantially concealed type hinges and fitted with nickel or chrome plated automobile type door handles which shall be fitted with suitable toggle to operate the rods so as to latch with suitable slots on both the top and bottom of the switchboards. Minimum size of the latching rods shall be 9.5 mm diameter or 19 mm x 4.8 mm flat and they shall be adequately guided by brackets space not more than 450 mm centres. The latching rods and associated brackets shall be cadmium plated. The instrument panel compartments of the switchboards shall have hinged doors and countersunk cadmium plated fixing screws.

All front side and top panels shall be constructed in a manner similar to that specified for doors

mentioned above. They shall be fitted from the inside of the switchboards by means of studs and cadmium plated washers and nuts.

11.6 Base Plate and Insulation Panels

The MCC/switchboard shall be of the front access type with removable panels that can be easily secured. Each panel shall have safety hinges to fix onto the switchboard and should not be larger in 1250mm width for easy removal.

All equipment shall be mounted on rigid base plates made of not less than 12 B.G. (2.5 mm thick)

sheet steel with folded edges and welded stiffeners wherever necessary. Whenever insulating panels are required to mount special equipment they shall be of high quality black bakelite, polished on the front and sprayed with four (4) coats of matt white on the back. All edges must be cut straight and squared and shall be chamfered on the front edge with 3.2 mm chamfer. Any defective or damaged panel shall be rejected and the Contractor shall replace it at his own expense.

11.7 Finishing and Metal Work

Panel work of the MCC/switchboards shall be finished smooth. All metal work shall be rust inhibited and have baked enamel finish of dark admiralty grey, externally and white internally.

The interior of the MCC/switchboard shall be illuminated by low voltage lamps, which will be switched

on when any portion of the cubicle is opened to provide adequate lighting on all equipment to which access has been gained.

After erection on site and after all inspection and tests have been carried out, the Contractor shall

thoroughly clean all parts, apply an additional coat of anti-corrosive structural priming paint to any part of the originally painted surfaces that have been scratched or otherwise marked and also apply at least one additional finishing coat as specified.

11.8 Busbar


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The design of the air-insulated busbar shall comply with B.S. 159, B.S. 1432 and/or B.S. 1433. They

shall be of tinned hard drawn high conductivity copper of adequate rectangular cross-section as determined in accordance with Singapore Standard CP5 : latest vension or IEE regulations for the electrical equipment of buildings to carry continuously the currents required or as detailed elsewhere in this Specification or accompanying Drawings. In any case, a current density of 155 amperes per sq. m (1,000 amperes per sq. in.) of cross sectional area shall not be exceeded.

Busbars and links shall be covered with plastic sheathing, coded to comply with the standard colour

code.

All joints in busbars shall be bolted or clamped with contact surfaces suitably prepared to prevent oxidation in service. Joints in copper busbar shall have tinned surfaces. They shall be rigidly supported to as to withstand any mechanical forces to which they may be subjected both during transport, erection and normal operation.

Busbar shall be supported on glass fibre reinforced polyester blocks or epoxy-resin blocks or resin

bounded paper or resin bonded laminated-wood or other approved insulating materials. The busbar supports shall be securely bolted to the structural frame of the cubicle. A neutral busbar shall be of the same cross-section as that for the phases. All bolts connections shall be secured by lock nuts.

The minimum busbar clearances between phases and between phases and earth shall not be less

than 38 mm and 32 mm respectively.

Busbars to MCCBs or other apparatus shall be made of circular busbars covered with Nylex tubing or rectangular section busbars covered with plastic sheathing in corresponding phase colour and terminated in core grip cable sockets or other approved termination.

All screws, bolts, washer and similar securing materials used for the construction of the switchboard

shall be cadmium plated.

All contact parts of the busbars and connections shall be sanded and coated with thin coat of chemically inert petroleum jelly.

11.9 Insulation

The clearance and insulation shall be such as to withstand the standard high voltage test on the switchgear.

All insulation used shall be of the best quality and sufficiently strong to withstand all stresses which

may be imposed on it in the ordinary erection and operation of the plant. Test results shall be submitted.

Where insulators are cemented or jointed to metal parts, such jointing shall be of such a nature that no

dangerous stresses are set up on the insulators by the unequal expansion or contraction of the insulation and the metal through range of temperature up to 40oC.

Attention is drawn to the possibility of bakelised paper being damaged by arching if unprotected with

consequent cracking, and unless arc controls are fitted, such bakelised paper shall be protected by a porcelain shroud or other approved means. The Tenderer shall state the protective means for protection.

Arrangements must be made to ensure that metal parts attached to bushings are maintained at fixed

potential under all conditions of operation.


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11.10 Phasing

Phase rotations shall be strictly maintained throughout the project, and shall comply with the requirements of B.S. 158.

Phase distinguishing colours shall be RED, YELLOW and BLUE.

11.11 Earthing

All metal parts of the switchboard and associated equipment shall be bonded and connected to a main earthing bar running throughout the entire length of the switchboard.

All earthing conductors shall be permanently connected to the main earthing bar.

All earthing provisions shall be made strictly in accordance with the requirements of PowerGrid and it

shall be the Contractor's responsibility to fully acquaint himself of all such requirements. 11.12 Neutral Links

Neutral links of incoming breakers shall be easily accessible and removable. Neutral links of all outgoing moulded case circuit breakers shall be removable and accessible from the

front. 11.13 Cable Entries

The switchboards shall house all necessary boxes, glands, etc. mounted vertically and arranged for front and rear access and connections. Provision for busbar connection to be done by Contractor.

Paper insulated lead-sheathed steel tape wire armoured or PVC/SWA/PVC cables shall be bottom

entries unless otherwise stated, whereas PVC/PVC and MICC cables shall be top entries. Cable boxes for termination of paper insulated lead-sheathed steel tape wire armoured cables shall be

mounted at base of the split type manufactured from good quality cast iron free from blow-holes complete with filling orifice, drain plugs, expansion dome, brass-cone shaped wiping gland of appropriate size, armour clamp and of such design as is suitable for attachment to the equipment served and such as to permit cable conductors to be formed into equipment terminals without undue bending.

Connections from switchboards gears to the busbar trunking shall be top entries and switchboard

stubs shall be included in the switchboard design.

11.14 Terminal Strips and Wiring

All incoming and outgoing and control circuits shall be wired to an approved centralized terminal strip, and the equipment at the inside of the cubicle shall be run via wiring channels and wiring outside the channels shall be run neatly and taped to the approval of the S.O. All wires shall be terminated with approved cable lugs, and separate cable lugs shall be used for each individual wire.

All wires shall be colour coded and shall have numbered ferrules at both ends. The ferrules shall be of white insulating materials having a glossy finished with the characters indelibly marked in black. Additional red ferrules marked "Trip" shall be fitted to the wires inter-connecting the relay trip contacts


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and the shunt release coils. All fuses and links shall be of the bakelite HRC type category 440/AC 4 class Q to B.S. 88

All wiring shall be arranged in a regular manner with bends set at 90 C and securely held in position

with suitable clips and where convenient shall be installed in the uprights and/or backstays, insulating bushes being used where necessary. They shall be formed in a neat and systematic manner.

Meter wiring of the switchboard shall be carried out in PVC insulated flame-proof switchboard cables of size not less than 1.5 sq. mm and enclosed in flexible plastic conduit. All meter wiring shall be of similar colours to those of the respective busbars etc., to which connections are made.

12.0 Cabling, Trunkings, Cable Trays and Conduits 12.1 Unless otherwise stated in the Drawings or Specification, all power cables between starters and motors shall be

in copper of 600/1000 V voltage grade, PVC insulated pvc sheathed cables to BS 6004 or SS 50. They shall be installed on galvanised cable tray, or in galvanised steel conduit. Where the cables on trays are installed less than 1.2m above floor level they shall be protected with galvanised steel cover. All cabling inside Chiller Plant Rooms for pumps, fans and other equipments shall be PVC/PVC insulated cables except for chillers, it shall be XLPE/PVC insulated cables. All cabling for equipments with emergency power supply shall be Fire Resistant cables.

12.2 Where PVC/SWA/PVC cables are indicated in the drawings, they shall be of copper and comply with BS 6346 (600/1000 V grade). All underground cables shall be PVC/SWA/PVC cables and terminated with BICC gland.

12.3 Where mineral insulated copper sheather (MICS) cables are indicated in the drawings they shall comply with

BS 6207: Part 1. MICS cables shall be installed in accordance with the manufacturer's instruction using proprietary fittings and accessories.

12.4 All power cabling sizes shall unless otherwise indicated in the drawings be adequately sized to cater for the

normal current rating and starting current of the equipment without undue overheating and stress. 12.5 Termination of power cable into motors or panel shall be through approved type of cast metal boxes with pvc or

brass glands and proper cable sockets. 12.6 All power cables shall be fixed on cable tray with approved pvc or brass saddles and clips at not more than 300

mm intervals.

12.7 All fire resistance type multi-core cables used shall conform to IEC 331 and BS 4066. 12.8 All underground cables shall be PVC/SWA/PVC cables and terminated with BICC gland. 12.9 All cabling for pumps, and other equipments shall be PVC/PVC insulated cables. All cabling for equipments with

emergency power supply shall be MICS/PVC insulated cables. 12.10 All cables shall be properly labelled by means of cable markers and cable ties shall be used to identify each set

of cables.


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12.11 All trunkings and cable trays shall be electro-galvanised and the thickness of trunkings and cable trays shall be

as follows:

Size of Trunking Thickness of Trunking

50 x 50 mm 1.219 mm (18 SWG)

50 x 75 mm 1.219 mm (18 SWG)

50 x 100 mm 1.219 mm (18 SWG)

50 x 125 mm 1.422 mm (17 SWG)

50 x 150 mm 1.422 mm (17 SWG)

50 x 200 mm and above 1.626 mm (16 SWG)

Size of Cable Tray Thickness of Cable Tray

50 mm 0.914 mm (20 SWG)

100 mm 0.914 mm (20 SWG)

150 mm 0.914 mm (20 SWG)

200 mm 1.219 mm (18 SWG)

250 mm 1.219 mm (18 SWG)

300 mm 1.219 mm (18 SWG)

375 mm and above 1.626 mm (16 SWG)

12.12 All metal parts, piping, etc, should be bonded to the earthing point by means of minimum 6 mm² PVC insulated

earth cable. 12.13 All metal conduits shall be galvanised steel manufactured and tested in accordance with SS 100. Minimum size

of conduit shall be 20 mm diameter. Space factor for cable in conduits shall not exceed 0.4 (40%). All metal conduits shall be of heavy-gauge type. All conduits shall be run neatly, concealed where possible, with runs truly horizontal or vertical or parallel to walls where conduits run in floors. Conduits shall be securely fixed with saddles and round head screws. Powered type of fittings will not be permitted. From outlet to outlet there shall be not more than four (4) normal bends or their equivalent. Inspection type conduit accessories shall be used throughout. Conduits shall be fixed in position before cables are drawn into them. The entire length of all cables shall be enclosed in conduit. Junction boxes shall be used at bends and "t" junctions. Elbows and tees will not be accepted.

12.14 All flexible conduits shall be metallic type. Flexible conduits which are exposed to weather or dampness shall

be of water-proof type with proper seals at connections to GI conduit and motor terminal box. Ordinary flexible conduit wrapped with PVC tape will not be accepted.

12.15 All circular junction boxes, pull boxes, inspection elbows, solid elbows shall be of malleable iron type and of

standard pattern with spout to BS 4568. All access covers for these accessories shall be provided with gaskets and lids.

12.16 Connections to all equipment subject to movement shall be in flexible conduit. Where they are exposed to water, oil or to the weather, the flexible conduit shall be of extruded pvc sheathed. Normal galvanised steel flexible conduit will not be acceptable.

12.17 Connections to the water tank's electrodes shall be of extruded pvc sheathed metallic type flexible conduit.


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12.18 All conduit and trunking shall be provided with saddles and bracket at not more than 1 m interval. 12.19 All conduit and trunking shall be finally painted to approval. 13.0 Outdoor Equipment 13.1 All outdoor equipment shall be provided with suitable weatherproof local start/stop control panel which shall be

mounted in close proximity to the equipment for servicing purposes and marked accordingly. Exact location of the local control panel shall be decided on site if not indicated.

13.2 All wiring to this equipment shall be PVC/PVC insulated and sheathed cables run in conduit/trunking. 14.0 Motors and Starters 14.1 All motor and starters shall be suitably tropicalised and the starters shall be incorporated with over current

release in each phase and a device to prevent single phasing as well as under voltage release. 14.2 All motors and starters shall comply with the current regulations of the SPPG. 14.3 All motors and starts shall be of approved make, and designed for operation in 400 V / 3 Phase / 50 Hz supply. 14.4 The following types shall be used (unless otherwise specified) :

Rating (kW)

V / Phase / Hz

Chiller Pump AHU FCU Cooling Tower

AHU (VAV)

Below 1.1 230/1/50 - - - - Split phase or capacity

VSD+DOL

Below 2.2 230/1/50 - - - - Split phase or capacity

VSD+DOL

2.2 - 11 400/3/50 - E/S+Y/D Y/D Y/D Y/D VSD+Y/D

11 & Above

400/3/50 E/S+A/T

E/S+A/T A/T A/T VSD+A/T VSD+A/T

D/L = Direct On Line A/T = Auto-Transformer Y/D = Star (Wye) Delta E/S = Electronic (Soft) Starter VSD = Variable Speed Drive

14.5 All starters shall be of uniform make irrespective of method of starting and shall be rated same as the motor

KW.


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14.6 Unless otherwise stated elsewhere in the specification and in the drawings, all motors shall comply with the

following: Three-Phase Motor: 400 Volts +/- 5% 50 Hz operation;

Single-Phase Motor: 230 V +/- 5% 50 Hz operation;

RPM: Not more than 1500 rpm unless otherwise approved

They shall be of squirrel cage induction type with totally-enclosed fan cooled enclosure.

They shall be continuously rated and designed to operate at the highest standard possible power

factor (min. 0.85) and efficiency (See SS 530) under all conditions of loading. They shall be of Class F insulation with a Class B permissible temperature rise.

They shall be equipped with cast iron made frames and brackets.

They shall be equipped with enclosed cast iron terminal to allow drilling and tapping to accept cables.

They shall be fitted with roller or deep groove ball bearings at the driving end and deep groove ball

bearing at the non-driving end. Motor driving equipment giving rise to end thrust shall be equipped with bearings designed to counter unbalanced end thrust. Bearings shall be selected for the duty in accordance with ISO recommendations and shall have a minimum life of 20,000 hours.

Motors shall be tested in accordance with the requirements of BS 2613 and BS 4999.

Where they are installed outdoor or exposed to the weather, they shall be of minimum IP 55. Submersible Motor Pumps shall be IP66 or IP67.

15.0 Terminal Strips and Wiring 15.1 All incoming and outgoing and control circuits shall be wired to an approved centralized terminal strip, and the

equipment at the inside of the cubicle shall be run via wiring channels and wiring outside the channels shall be run neatly and taped to the approval of the S.O. All wires shall be terminated with approved cable lugs, and separate cable lugs shall be used for each individual wire.

15.2 All wires shall be colour coded and shall have numbered ferrules at both ends. The ferrules shall be of white

insulating materials having a glossy finished with the characters indelibly marked in black. Additional red ferrules marked "Trip" shall be fitted to the wires inter-connecting the relay trip contacts and the shunt release coils.

15.3 All fuses and links shall be of the bakelite HRC type category 440/AC 4 class Q to B.S. 88. 15.4 All wiring shall be arranged in a regular manner with bends set at 90 C and securely held in position with

suitable clips and where convenient shall be installed in the uprights and/or backstays, insulating bushes being used where necessary. They shall be formed in a neat and systematic manner.


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15.5 Meter wiring of the switchboard shall be carried out in PVC insulated flame-proof switchboard cables of size not

less than 1.5 sq. mm and enclosed in flexible plastic conduit. All meter wiring shall be of similar colours to those of the respective busbars etc., to which connections are made.

15.6 All terminals shall be fitted with brass washers and securely fixed with lock nuts to an approved type of terminal

block placed in an easily accessible position for testing at site. 15.7 No connectors or soldered joints shall be permitted in the wiring. 15.8 Power cable and control cable shall be installed in separate conduit/trunking. 16.0 Moulded Case Circuit Breakers (MCCB) 16.1 General

Moulded case circuit breakers shall conform to the latest British Standard BS 3871 part 2 or NEMA Standard AB1 and U/L listed.

All MCCB shall have minimum interrupting capacities of R.M.S. symmetrical amperes at 400 Volts A.C.

for 3 sec. All MCCBs in switchboard or distribution panel board shall be of the same make.

All MCCBs of 600 AF and above shall be provided with easy operating handles.

All MCCBs feeding to feeder/plug in bus-ways shall be of the current limiting type.

16.2 Operation

Moulded case circuit breakers shall be operated by a toggle type handle and shall have a quick-make over-centre switching mechanism that is mechanically trip free from the handle so that the contacts cannot be held-closed against short circuits and abnormal currents. Tripping due to overload or short circuit shall be clearly indicated by the handle automatically assuming a position midway between the manual "ON" and "OFF" positions. All latch surfaces shall be as constructed that they open, closed and trip simultaneously.

16.3 Construction

Each of these breakers shall provide inverse time delay and instantaneous circuit protection by means of thermal magnetic element. Ambient compensation shall be accomplished by a secondary bi-metal that will allow the breaker to carry rated current between 25°C and 50°C with tripping characteristics that are approximately the same throughout this temperature range.

Breakers shall be completely enclosed in a moulded case. Non-interchangeable trip breaker shall have

their cover sealed; whereas interchangeable trip breaker shall have the trip unit sealed to prevent tampering. Contacts for circuit breaker shall be of non-welding silver or silver alloy.

Manual trip button and front-adjustable magnetic trip device shall be incorporated in the moulded case

circuit breaker. Arcing shall be extinguished rapidly and effectively by Arc-extinguishing device, in normal switching as

well as protective tripping, to minimise deterioration of contacts and adjacent insulating materials.


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Terminals shall be constructed to assure electrical efficiency and reliability, with minimised possibility

of localised heating. Trip indication shall be by handle position mid-way between 'ON' and 'OFF'. To reset the trip

mechanism, the handle shall be moved to extreme 'OFF' and 'ON' position. For current limiting (CL) moulded case circuit breakers, the current limiting breakers shall be fuseless

type and shall have the same operation as specified above. They shall meet the IEC requirements and shall be UL listed. All three phases shall be opened simultaneously under fault conditions. The breakers shall have interrupting ratings as low as 10KA rms, sym. on systems capable of delivering fault currents as high as 200KA, rms, sym. The contact opening and are extinguishing shall be less than ¼ cycle to reduce and limit peak let-through current and let-through energy.

17.0 Low Voltage Air Circuit Breakers 17.1 General

Low voltage air-circuit breaker shall be of metal-clad, flush mounted horizontal draw-out isolation type. They shall comply fully with B.S. 4752 and applicable part of B.S. 116 and B.S. 936 and shall have a rupturing capacity of not less than 43KA at volts A.C. 50 HZ for 3 sec. in accordance with the above specifications certified by ASTA or KEMA or other recognised testing authority. Low voltage air-circuit breaker shall incorporate direct acting tripping device which shall operate at 15% or 200% of the rated current.

17.2 Construction

Each air circuit breaker shall be self-contained with specifically designed rollers, runner rails and interlocks and housed in a separate completely zoned "Enclosed Ventilated" metal clad switchboard compartment. The circuit shall comprise fixed and moving main arcing contacts of adequate rating to ensure that no overheating, damage or deterioration will arise when carrying continuously full rated current. The contacts shall be individually spring loaded and hard silver plated, so arranged that electro-magnetic forces arising from under fault conditions do not tend to reduce contact pressure. The main contacts shall be arranged to give a double break in each pole. Auxiliary arcing contacts shall be provided with renewable arc resisting alloy tips arranged to close before and open after the main contacts. Each pole of the breaker shall be equipped with individual arc chutes with specially designed baffles and splitter to provide effective and efficient electro-magnetic arc control at all values of load current. Any arc caused by the opening of the breaker under maximum fault conditions shall be completely contained in the chute with no possibility of a "Flashover" between phases or between any phase and neutral or between adjacent earthed metal. The complete chute assembly shall be easily removed for routine inspection and maintenance of the chute and contacts. Safety screening shutters of insulation materials to prevent access to live connections shall be actuated automatically with the circuit breaker isolated and withdrawn. Provisions shall be made for padlocking the safety screening shutters when the breaker is completely withdrawn.


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Auxiliary switches, relay isolating plugs and sockets, and contactors as necessary for the proper operation of the circuit breaker, trip coils, electrical interlocks, and "operation status' indication shall be provided. In addition to those required for the functions covered in this specification, provision shall be made for extending the number of auxiliary switches on each circuit breaker to cover possible future alarm or signalling circuit requirements. Auxiliary switches shall be of robust double breaker design, easily accessible for maintenance, having adequate current ratings to carry the connected loads. Earth terminals shall be provided at the rear of the withdrawable breaker housing. This connects to a plug and socket contact to provide an earth connection to the moving breaker portion. Contact shall be maintained in the breaker isolated position. Mechanical interlocking shall be provided to prevent: opening of cubicle door until breaker is fully isolated

withdrawal of plugging of the circuit breaker in the closed position

plugging until the cubicle door has been closed and locked

closure unless either fully plugged or fully isolated

17.3 Operation

The circuit breaker of stored energy spring manually charged type with manual release of the spring by means of the "Close" push button. It shall incorporate an interlock which prevent a close operation until spring is fully charged. Tripping shall be carried out means of a 'trip' button, operation of overcurrent trip and shunt trip release. The speed of closing and opening of the circuit breaker shall be independent of the operation. Breaker 'ON' - 'OFF' and spring 'Charged' -'Discharged' indications shall be provided. The shunt trips coils for operating the release mechanism of the circuit breakers shall be controlled by push-button and/or circuit closing relays. They shall be designed for operation from a supply source. The mechanism shall be stable and not capable of being opened by shocks or jam. The design of the trip coil shall be such that the trip plunger shall be operated immediately there being no delay due to the building up of the coil field to maximum value. The use of fibre in the construction of the trip coils will not be acceptable, being preferred that the trip coils be wound on a high grade bakelite on mica former. The operation mechanism and the carriage or hinged panel shall be so interlocked that it is not possible to withdraw or replace the circuit breaker while the breaker is in the closed position, so that it is not possible to close the breaker while the carriage or hinged panel is in any position between "fully isolated' and "full home" or vice versa. Provision shall be made so that it is possible to operate the breaker mechanism, if required for inspection and testing purposes, when the breaker is fully isolated. Provision shall also be made to prevent the breaker being accidentally pulled completely off the guide rails.

18.0 Colour Codes and Labels 18.1 Corners and bases shall be coloured in accordance with the following code:

Colour Function

White 5A fuse

Blue 15A fuse

Yellow 20 fuse


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Red link

18.2 Descriptive labels shall be fitted, adjacent to all fuses and links. 18.3 The terminal strip shall be numbered and schedule so as to identify the particular circuits without difficulty. The

same numbers and reference letters identifying circuits and/or components of the equipment shall be shown on the wiring diagram which is to be supplied by the Contractor.

18.4 The interior of each piece of equipment shall be clearly marked to show the phases and to this end either coloured plastic discs screwed to fixed components or identification by means of colour plastic sleeving shall be employed. Plastic tape will not be permitted.

19.0 Labels 19.1 All equipment shall be clearly labelled in accordance with regulations, and to indicate its functions by means of

engraved traffolyte ivorine labels (Block in white lettering for normal supply, Red in white lettering for emergency supply).

19.2 Each circuit breaker, switch, switch-fuse, fuse, selector switch, indicating light, push button, instrument, etc.

shall be labelled indicating its rating, function, designation. In addition warning signs marked "400 volts Danger" manufactured to standard design and colour shall be suitably mounted and fixed on the back of the incoming cubicles on the front of each switchboard and on the door of the switchroom. The marking shall be in accordance with BS 171 clause 79.

20.0 Current Transformers (C.T.) 20.1 Current transformers necessary for the operation of instruments and meters shall be of "straight through" type,

with accuracy not less than class 'C' for measuring, class 'CM' for metering and class 'S' for protection as per CP 5:latest version.

20.2 Current transformers shall be adequately rated in V.A. to carry the summation of all V.A. burdens of connected

loads, and shall be capable of carrying currents of the corresponding circuit breakers and fuses. They shall be capable of operation, without damage, with open circuited secondary and full load current flowing in the primary. They shall comply with the latest PUB requirements.

20.3 Current transformers shall be adequately supported and installed as to permit easy access and to be readily

replaceable, if necessary, without dismantling of adjacent equipment. 21.0 Instruments and Meters 21.1 Instruments and meters for external panel mounting shall be flush mounting, square or rectangular type with

moulded plastic escutcheons and shall conform to the requirements. 21.2 Reading scales in kilo-watt hour meters shall be in multiple of ten (10). 21.3 All instruments shall be to B.S. 89 1st grade, moving iron spring controlled with 100 mm diameter dials (240°

scale) with external zero adjustment. Integrating meters shall be to B.S. 37 part 1 and 2 : latest version and part 4 : latest version with cyclometer registers and shall be calibrated for use with their respective current transformers. They shall be fully tropicalised.

21.4 Voltmeters shall incorporate selector switches to enable phase to phase and phase to neutral voltage to be read. Ammeters shall have selector switches to read all the line currents. Selector switches shall be of approved rotary type.


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22.0 Overcurrent Relays 22.1 The over current relays shall be IDMTL adjustable current setting between 50% to 200% of rated values and

adjustable time lag settings of 0 to 3.0 seconds; instantaneous high set elements shall be provided for each main circuit breaker.

22.2 The relays shall be of the surface mounted and housed in a totally enclosed dust-proof switchboard module. 22.3 The operating coils and contacts shall be adequately rated to carry the necessary load. Operation indicator and

reset facilities shall be provided. 22.4 The relays shall be heavy pattern, unaffected by external vibration, fully tropicalised and capable of operation in

any position. 23.0 Earth Fault Relays 23.1 The relays shall be heavy pattern, unaffected by external vibration, fully tropicalised and capable of operation in

any position. 23.2 The earth fault relays shall incorporate adjustable current setting between 5% to 40% in steps of 5% and

adjustable time lag 0 to 1 sec. 23.3 The relays shall be of the flush pattern and housed in removable dust-proof sheet metal casings provided with

viewing glass or clean plastic. 23.4 The operating coils and contacts shall be adequately rated to carry the necessary load. Operation indicator and

reset facilities shall be provided to show a fault condition. 23.5 The relays shall be heavy pattern, unaffected by external vibration, fully tropicalised and capable of operation in

any position. 24.0 Indicating Lamps

Indicating lamps shall be the durable LED type (5-years full replacement warranty). The lamp shall be easily removed or replaced from the front of the panel without using extractors and shall be adequately ventilated.

25.0 Moulded Case Circuit Breakers (MCCB), Contactors, Isolators, etc.

Moulded case circuit breakers, contactors, isolators and other items where applicable and necessary shall be provided to comply with the relevant clauses specified elsewhere in the Specification.

26.0 Miniature Circuit Breakers (MCB) 26.1 General

Miniature circuit breakers shall comply with the latest British Standard BS 3871 with latest amendments. Unless otherwise stated, miniature circuit breakers and distribution boards shall have minimum short-circuit capacities of R.M.S. symmetrical amperes of 10 KA for power circuit distribution boards at 240/415 Volt A.C.


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All miniature circuit breakers (MCB) shall have tripping characteristic type "3" curve. Irrespective to the mounting positions, the miniature circuit breakers shall be operated in accordance with the factory calibrated characteristic. All miniature circuit breakers shall be of positive plug-on or bolted-on, no error connection type. Miniature circuit breaker must have positive contact position indicator.

26.2 Operation

Miniature circuit breakers shall be operated by a toggle-type handle and shall have a quick-made, positive quick-break over centre switching mechanism that is mechanically trip free from the handle so that the contacts cannot be held close against short circuits and over current conditions. When the circuit breaks and over current conditions. When the circuit breakers automatically trip, the operating handle shall be assured a position between "ON" and "OFF" positions. The contacts shall also be of positive quick-make and quick-break on manual and automatic operation. Contact position indicator (coloured) linking physically to the contacts for the positive indication of isolation shall be provided. Two and three pole circuit breakers shall be commonly trip with individual spring pressure on each contact.

26.3 Construction

Each pole of the circuit breakers shall have a factory calibrated thermal bi-metal overcurrent element with inverse time delay characteristic and a factory calibrated instantaneous magnetic tripping device for short circuit condition. Ambient temperature compensation shall be accomplished by a secondary bi-metal that shall allow the circuit breaker to carry rated current between 25 C to 50 C with tripping characteristics that are the same throughout this temperature range, and that shall not cause nuisance tripping. Circuit breakers shall be completely enclosed in a high dielectric strength casing. The properties of the dielectric strength casing shall not deteriorate with time. Contacts of circuit breaker shall be non-welding silver-tungsten. The high pressure plug-on busbar connector shall assure a solid positive contacts without screw to tighten and no chance of error. Load terminals shall be constructed to assure electrical efficiency and reliability, with minimized possibility of localised heating, and for straight in wiring. Arcing shall be extinguished rapidly and effectively by arc chute barrier, in normal switching as well as protective tripping, to minimize deterioration of contacts and adjacent insulating materials. Trip indication shall be by means of the handle position lying between "ON" and "OFF". To reset the trip mechanism, the handle shall be moved to extreme "OFF" position.


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27.0 Distribution Boards for VAV Boxes Power Circuits 27.1 General

A distribution board shall be incorporated within the Air Handling Unit's local control board for the VAV boxes power circuits. One number of minimum 13A switched socket outlet (SSO) or higher rating (appropriate for the VAV wattage) shall be provided for each VAV box and the electricity supply shall be connected from this distribution board. A maximum of four (4) 13 Amp switched socket outlets can be connected to each outgoing circuit. Circuit Breaker Distribution Boards shall be of the dead-front safety type equipped with thermal magnetic miniature circuit breakers of the frame sizes, types and ampere trip ratings specified on the accompanied distribution board drawings. All distribution boards shall be rated at 240 Volt A.C. 50 Hz 2 wire supply and shall comply with the latest British Standard BS 5486 part 12 for distribution boards or British Standard BS 5486 part 13 for consumer units. All miniature circuit breakers (MCBs) and circuit breaker distribution boards shall be from the same manufacturer. All circuit breaker distribution boards shall be of the approved type. The minimum short-circuit capacities of R.M.S. symmetrical amperes of circuit breaker distribution boards and incoming circuit breakers, if applicable, shall be of the same KA rating of the specified short-circuit capacities of the miniature circuit breaker. The interior assembly for the connection and mounting of MCB must be of good quality, type tested and approved type. Original blanking plates shall be used for space(s) (i.e. outgoing way(s) without miniature circuit breaker(s)) as indicated in the Drawings.

27.2 Construction

The distribution boards shall conform to the following construction to form a single or group of boards as indicated on the Drawings. Bussing Assembly and Temperature Rise Distribution board bus structure shall have the same current rating of the incoming breakers as shown on the accompanied distribution boards drawings. In any case, a current density of min. 155 Amperes per sq. cm (1,000 amperes per sq. in.) of cross-sectional area shall be maintained. However, the ratings shall also be established by heat riser tests with maximum hot spot temperature on any connector or busbar not exceeding 50°C rise above ambient temperature. Adequate conductor dimension will not be accepted as an excuse for foregoing actual heat tests. Busbars shall be of tinned hard drawn copper. Pre-drilled copper neutral bar of full current rating and pre-drilled copper earth bar of size equal to incoming feeder earth cable shall be provided and neatly arranged. Neutral and earth bars shall be of solder-less mechanical type connectors. The neutral bars shall be mounted to the distribution boards by non-hygroscopic insulators. The insulation of resistance for neutral bars to the metal enclosure shall be infinity and for earth bars to the metal enclosure shall be zero. The number of connector holes in the neutral and earth bars shall be equal to the number of branch circuit breakers ways plus one for incoming feeder neutral or earth cable. Phase bussing shall be full length without reduction. Busbar taps for distribution boards with single pole branches shall be arranged for sequence phase connection of the branch circuit devices which allows complete flexibility of circuit arrangement.


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Miniature Circuit Breakers (MCBs) Miniature circuit breakers shall be equipped with individually insulated, braced and protected connectors. The front face of all miniature circuit breakers shall be flush with each other. Space provisions for additional circuit breakers shall be so designed that additional breakers shall be plugged-on to the bus-tap by pressure without using additional connectors, cable or copper bar links, modification or alteration to the distribution board. Integrated Equipment Rating Each distribution board, as a complete unit, shall have a rating equal to or greater than the integrated equipment rating shown on the drawings. Such rating shall be established by test with the circuit breakers mounted on the distribution boards. The short-circuit tests on the circuit breaker and on the distribution structure shall be made simultaneously by connecting the fault to each distribution board circuit breaker with the distribution board connected to its rated voltage source. The method of testing shall be as per proposed British Standard (B.S.) pertaining to listing of miniature circuit breakers for high-short circuit capacity ratings. The source shall be capable of supplying the specified distribution board short-circuit current or greater.

Safety Barriers The distribution board interior assembly shall be dead front with distribution board front removed. Also, it shall be possible to change branch circuit load connections without personal exposure to any live side bussing on live terminals. Spaces for future installation of circuit breakers shall be covered by clip-on type of non-metallic plates. Main lugs or main circuit breaker shall be barricaded on live sides. The barrier in front of the main lugs shall be hinged to a fixed part of the interior. The end of the bus structure opposite the mains shall be barricaded. All distribution board shall also be designed for bottom incoming and top outgoing circuitry unless otherwise stated.

27.3 Labelling

Large permanent individual number shall be affixed permanently to each branch miniature circuit breaker and main incoming circuit breaker in a uniform position. Each individual cable shall be numbered with numbered ferrules or approved equal according to the 'As Built' distribution board drawings and the Contractor shall in addition hang a good quality plastic bag with a copy of floor plan or portion of the floor plan which is served by the associated distribution board, and type-written table showing the circuit numbers and designations in approved arrangement according to the 'As Built' circuit breakers layout of each distribution board, beside the distribution board. All neutral and earth continuity conductor shall be installed in sequence and numbered with grafoplast cable marking system according to the circuit numbers of the "As-Built" distribution boards drawings. All neutral and earth bar connectors shall have clear permanent numbers for easy identification. The numbers shall be in sequence. All distribution boards shall be clearly, permanently labelled according to the "As-Built" distribution boards drawings by grafoplast cable marking system and self-adhesive label holders.


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28.0 Testing 28.1 All electrical installation works shall be tested in accordance with the requirements of SS CP 5 and the local

authorities. All test results shall be submitted to the S.O. for approval before turn-on of power. 28.2 The Contractor shall be responsible for all Electrical tests at the site and shall be represented by a capable

during the whole of the period required for the tests. 28.3 All materials and equipment supplied or erected under this Sub-Contract which fail the tests shall be replaced or

rectified at once by the Contractor without cost to the Employer and the tests shall be repeated. 28.4 All tests shall be conducted in the presence of and to the satisfaction of the S.O. The Contractor shall supply all

necessary instruments, apparatus, connections, skilled and unskilled labour required for the tests to the satisfaction of the S.O. and the cost of doing so shall be included in the Sub-Contract price.

28.5 The Contractor shall make accurate records of all tests and shall furnish test certificates and a schedule of the results in an approved form. Four copies of such schedules and of each test certificate will be required.

28.6 Any circuit or section of the installation failing to reach the required standard for acceptance shall be made good

by the Contractor without cost to the S.O.

28.7 The minimum of site tests to be carried out on each completed section of the electrical installation shall be as follows:

28.7.1 Insulation resistance tests. Continuity Tests.

Tests to prove correct operation of interlocks, tripping and closing circuits, indications, etc.

Protective gear timing tests as may be necessary.

Test operation of alarm devices.

Rational tests on all motors.

Polarity tests to verify that single pole switches are installed in the phased or live conductor of each

circuit and not in the neutral conductor. A test to verify the continuity of all conductors in every ring circuit, correct connections to terminals or

all socket outlets and effective bending to earth of each terminal and socket. Insulation resistance tests to earth and between conductors before and after fitting of lamps. The

standard of acceptance for electrical insulation tests shall be as recommended in the latest Edition of the IEE Regulations for the Electrical Equipment of the Building.

Insulation resistance tests on any electrical apparatus supplied and/or erected under this contracts

before and after connecting such apparatus to the supply. Earth continuity tests for each final sub-circuit and the completed installation to ensure that the

impedance of the earth fault loop is such as to permit compliance with the requirements of Section D and E of the latest Edition of the IEE Regulations for the Electrical Equipment of Buildings.


13119BM

29.0 Certification by Contractor (Under Contractor)

Before any turning-on of power can be made to the Installations, the -Contractor shall certify in writing to the S.O. that his electrical installation is in full compliance with the PUB Regulations and that it is safe for turn-on. The certificate shall be signed by a PowerGrid licensed electrical worker, employed by the Contractor and qualified to sign for the capacity of the installation involved. Test results shall accompany this certification.

30.0 Safety Notices

The Contractor shall provide and install the following notices and equipment in the A/C Chiller Plant Room.

30.1 A varnished and mounted on suitable hard backing and framed (in glass panel) copy of the main single line diagram showing clearly the full details, dimensions, layout of the switchboards as supplied and installed.

30.2 Solid rubber insulated mats of 1 meter wide and 9.5 mm thick complying with B.S. 921 to the full length in front of every switchboard.

electrical works specifications (acmv)

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