The installation of self contained emergency lights is a statutory requirement in most countries. They need to be provided at strategic places throughout the building in order to aid the evacuation of the building occupants out of the building in the event of failure o the mains supply.
The need for these emergency lighting is real even during daytime because some internal corridors inside the building are actually too dark without some form of lighting. The emergency lights are meant to provide the minimum illuminance needed for a safe and orderly movement of the people.
The self contained emergency light fittings are usually installed at all exit routes and at all places where uninterrupted lighting is required. In the second situation this lights serve the dual functions of a fire related equipment and a normal lighting (with much reduced lighting level).
The emergency light fittings are connected to the essential supply of the building electrical system. This way the rechargeable storage battery is charged even during normal power failure (i.e. when the standby electrical generator is running).
The exact quantity and the exact locations of these emergency light fittings are usually recommended by the Fire Department. In practice, a licensed architect is required by law to submit the building design plans to the Fire Department for approval before the building construction commences.
The architect would need to incorporate these lighting into their fire protection design schemes in order to obtain the Fire Department’s approval.
This layout is part of what is normally called the “static fire protection”. Those services like the wet risers, etc are called active fire protection and they will need to be submitted by licensed professional mechanical engineers to the Fire Department after the passive fire protection schemes (submitted by the architects) have been approved.
Prior to the submission by the architect, the electrical engineer’s input may be requested by the architect with respect to the quantities and locations of the emergency lights. However this task has become so routine that the engineer’s advice on this aspect is rarely necessary.
After the approval has been obtained, the approved layout of the emergency lighting is binding and it has become an input and a minimum design requirement for the electrical engineer. She can add more of the emergency light fittings into the design, but she cannot omit or change what has been approved in the submitted drawings.
That is basically the principle.
In addition to the self contained emergency lights that are required by the fire department, some of the general lighting luminaries are also connected to the essential supply that has been backed by the standby generator. This is sometimes done to supplement the lighting provided by the self contained emergency lights.
More often, however, this is done to provide some level of general lighting that can allow normal work to continue even in the event of normal power failure. Of course power failures caused by fire conditions demand a different course of actions immediately from all the building occupants.
There is one more lighting component that is closely related to the self contained emergency lights, that is the “EXIT” sign.
The Exit signs are also required by law similar to the emergency lights. They must be provided at all exit doors of all buildings and all floors, and at each location where the fire emergency exit routes change direction.
Similar to the emergency lights, these components are included in the proposed static fire protection submitted by the architects to the Fire Department.
An approved layout of this fire component will become a minimum design requirement to the electrical engineer. She can add more of the lighted Exit signs, but she cannot reduce them or change them.
Like the emergency lights also, the Exit signs are self-contained, battery operated. The difference between the two is that the Exit signs are always on.
See pictures of electrical installations by visiting this post, Free electric installation pictures.
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Showing posts with label Main switchboard. Show all posts
Showing posts with label Main switchboard. Show all posts
Friday, December 18, 2009
Thursday, December 17, 2009
Electrical MCCB installation
This section lays out the major performance requirements for the MCCB (moulded-case electrical circuit breakers) installation inside switchboards.
All moulded-case circuit breakers shall comply with IEC 60947-2.
All electrical MCCB shall be of moulded insulating material of good mechanical strength and non-tracking properties. The tripping mechanisms shall be calibrated in compliance with IEC standards at the factory and the breaker shall be sealed to prevent tampering.
The MCCB shall be so designed that when on tripped condition, the circuit breaker cannot be switched on unless it has been reset by switching it to the OFF position first. The operating condition (i.e. ON, OFF or TRIP) of the circuit breaker shall be clearly indicated. The construction and operation of the MCCB installation shall be such that if a fault occurs, all the poles of the breaker shall operate simultaneously to isolate and clear the fault efficiently and safely without any possible risk to the operator or to the installation.
Each MCCB shall incorporate a ‘trip-free’ mechanism to ensure the breaker cannot be held closed under fault conditions. The operating mechanism of the circuit breaker shall be hermetically sealed at the factory and all metallic parts associated with the operating mechanism shall be treated against rust and corrosion.
Bolt-in type solid neutral links shall be provided and fitted in the same compartment together with the phase poles.
Means shall be provided to padlock the MCCB in the ‘OFF’ position. Mechanical ‘ON/ OFF’ indicator operating in conjunction with the rotary type operating handle of the circuit breaker must be provided.
MCCBs supplying loads from switchboards connected to the emergency power system shall be provided with facilities for remote operation (OPEN and CLOSE) and auxiliary contacts for remote indication.
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All moulded-case circuit breakers shall comply with IEC 60947-2.
All electrical MCCB shall be of moulded insulating material of good mechanical strength and non-tracking properties. The tripping mechanisms shall be calibrated in compliance with IEC standards at the factory and the breaker shall be sealed to prevent tampering.
The MCCB shall be so designed that when on tripped condition, the circuit breaker cannot be switched on unless it has been reset by switching it to the OFF position first. The operating condition (i.e. ON, OFF or TRIP) of the circuit breaker shall be clearly indicated. The construction and operation of the MCCB installation shall be such that if a fault occurs, all the poles of the breaker shall operate simultaneously to isolate and clear the fault efficiently and safely without any possible risk to the operator or to the installation.
Each MCCB shall incorporate a ‘trip-free’ mechanism to ensure the breaker cannot be held closed under fault conditions. The operating mechanism of the circuit breaker shall be hermetically sealed at the factory and all metallic parts associated with the operating mechanism shall be treated against rust and corrosion.
Bolt-in type solid neutral links shall be provided and fitted in the same compartment together with the phase poles.
Means shall be provided to padlock the MCCB in the ‘OFF’ position. Mechanical ‘ON/ OFF’ indicator operating in conjunction with the rotary type operating handle of the circuit breaker must be provided.
MCCBs supplying loads from switchboards connected to the emergency power system shall be provided with facilities for remote operation (OPEN and CLOSE) and auxiliary contacts for remote indication.
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Electrical busbars
The electrical busbars inside the switchboards shall be of plain hard-drawn, high conductivity, electrolytic copper bars in accordance with BS EN 13601: 2002, and of adequate rectangular cross-section to carry continuously the specified current without overheating and shall be rigidly mounted on non-hygroscopic insulators so as to withstand any mechanical forces to which they may be subjected under maximum fault condition.
Busbars shall be colored red, yellow, blue and black at appropriate points to distinguish the phases and neutral. No tapes shall be used. The main busbars shall be arranged in a horizontal plane and in the order of red, yellow, blue and neutral phases from back to front. On each panel connections shall be red, yellow, blue and neutral phases from left to right viewed from the front of the panel.
The phase and neutral busbars should be located in the top compartments of the switchboard.
The busbar system shall be readily accessible for inspection, construction and maintenance duties without the requirement of additional equipment. In case of a busbar short circuit, it shall be possible to clean or to replace the busbars and the support system without stripping the assembly.
In the busbar compartment the phase busbars may not be fully insulated. However, each phase busbar shall be able to withstand at least an applied AC test voltage of 2.5 kV for a period of 60 seconds.
The droppers shall have full segregation by insulated materials. The insulation of the busbar jointing and branching points shall be of equal quality to that of the main bars and shall be removable and easily replaceable for inspection.
The neutral bar may be not insulated in the busbar compartment but shall be insulated at all other compartments with the same insulation level as the phase busbars.
The earth bar shall be located in the top or bottom compartment and in all cable riser compartment of the switchboard and shall be easily accessible. Sufficient connection points with adequate terminating facilities shall be provided for terminating the cable earth leads. The earth bar shall be sized complying with IEC 60439-1.
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Busbars shall be colored red, yellow, blue and black at appropriate points to distinguish the phases and neutral. No tapes shall be used. The main busbars shall be arranged in a horizontal plane and in the order of red, yellow, blue and neutral phases from back to front. On each panel connections shall be red, yellow, blue and neutral phases from left to right viewed from the front of the panel.
The phase and neutral busbars should be located in the top compartments of the switchboard.
The busbar system shall be readily accessible for inspection, construction and maintenance duties without the requirement of additional equipment. In case of a busbar short circuit, it shall be possible to clean or to replace the busbars and the support system without stripping the assembly.
In the busbar compartment the phase busbars may not be fully insulated. However, each phase busbar shall be able to withstand at least an applied AC test voltage of 2.5 kV for a period of 60 seconds.
The droppers shall have full segregation by insulated materials. The insulation of the busbar jointing and branching points shall be of equal quality to that of the main bars and shall be removable and easily replaceable for inspection.
The neutral bar may be not insulated in the busbar compartment but shall be insulated at all other compartments with the same insulation level as the phase busbars.
The earth bar shall be located in the top or bottom compartment and in all cable riser compartment of the switchboard and shall be easily accessible. Sufficient connection points with adequate terminating facilities shall be provided for terminating the cable earth leads. The earth bar shall be sized complying with IEC 60439-1.
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Wednesday, December 16, 2009
Switchboard electrical earthing
Following is a picture showing the earthing busbar of a main switchboard. Below the picture is a simple performance specifications for the grounding of the switchboard.
The are also two more posts on switchboard installation check and switchboard electrical tests. The latter is a general list of tests and inspections that are usually required of a major switchboard such as main switchboards and large subswitchboards.
Photo 1 - Earthing busbar of a main switchboard (MSB)
The earthing of an electrical switchboard shall be in accordance with BS 7430, and the color coding of protective conductors shall be in accordance with IEC 60646.
Switchboard earthing busbar
The switchboard earthing busbar shall be installed internally along the full length of the switchboard. The material of the busbar shall be the same as the material of the phase busbars. (See more photos: Switchboard earthing busbar.)
Equipment earth bar
Where the substation consists of 11 kV switchgears, transformers and LV switchboards, earthing copper tape shall be installed continuously along the full length of the substation.
It shall be connected to the main system earth bar at both ends using appropriate size earthing bolts with nuts and spring washers.
The earthing copper tape shall be made of hard-drawn high conductivity copper.
The cross-section of the earth bar shall be sufficient to carry the rated short-time withstand current of the switchgear for the allowable temperature rise and the time specified.
Internal branch earth connections
The branch earth connections made from the switchboard earthing busbar to the individual switchboard components shall consist of adequately sized copper strips, or green/ yellow striped PVC sheathed stranded copper conductor.
The termination lugs shall be of the compression type.
Earthing of metal parts
All metal parts of a switchboard where live components (such as relays, instruments, indicating lights etc) are mounted shall be earthed through branch connections to the switchboard earthing busbar.
Doors of the switchboard shall also be similarly earthed.
Frames of the draw-out circuit breakers shall be connected to the earthing busbar through a substantial plug type earthing contact.
Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.
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The are also two more posts on switchboard installation check and switchboard electrical tests. The latter is a general list of tests and inspections that are usually required of a major switchboard such as main switchboards and large subswitchboards.
Photo 1 - Earthing busbar of a main switchboard (MSB)
The earthing of an electrical switchboard shall be in accordance with BS 7430, and the color coding of protective conductors shall be in accordance with IEC 60646.
Switchboard earthing busbar
The switchboard earthing busbar shall be installed internally along the full length of the switchboard. The material of the busbar shall be the same as the material of the phase busbars. (See more photos: Switchboard earthing busbar.)
Equipment earth bar
Where the substation consists of 11 kV switchgears, transformers and LV switchboards, earthing copper tape shall be installed continuously along the full length of the substation.
It shall be connected to the main system earth bar at both ends using appropriate size earthing bolts with nuts and spring washers.
The earthing copper tape shall be made of hard-drawn high conductivity copper.
The cross-section of the earth bar shall be sufficient to carry the rated short-time withstand current of the switchgear for the allowable temperature rise and the time specified.
Internal branch earth connections
The branch earth connections made from the switchboard earthing busbar to the individual switchboard components shall consist of adequately sized copper strips, or green/ yellow striped PVC sheathed stranded copper conductor.
The termination lugs shall be of the compression type.
Earthing of metal parts
All metal parts of a switchboard where live components (such as relays, instruments, indicating lights etc) are mounted shall be earthed through branch connections to the switchboard earthing busbar.
Doors of the switchboard shall also be similarly earthed.
Frames of the draw-out circuit breakers shall be connected to the earthing busbar through a substantial plug type earthing contact.
Note: This anchor post, Free electric installation pictures , may contain a summary of the materials you are looking for. It can be faster than clicking through each post title at the Blog Archive. I started it long ago but never actually got around to finish it.
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Switchboard electrical tests
The following electrical tests must be carried to all switchboards, sub-switchboards, main distribution boards and motor starter panels.
A. Full type tests
1) Full type tests shall be carried out in accordance with IEC 60439-1, IEC 60947-1, and IEC 60947-6-1. Certificates issued by approved independent testing laboratories shall be submitted to the Employer’s Representative.
The type tests shall include the following:
a) Verification of temperature-rise limits
b) Verification of the dielectric properties
c) Verification of the short-circuit withstand strength
d) Verification of the effectiveness of the prospective circuit
e) Verification of the clearances and creepage distances
f) Verification of mechanical operations
g) Verification of the degree of protection
B. Routine tests
Before the product leaves the works, the manufacturer shall carry out the relevant routine tests in accordance with IEC 60439-1 on the total assembly, and the IEC 60947-1 and IEC 60947-6-1 parts thereof when delivered with time intervals, and the results shall be recorded in a test report.
C. Special tests
Carry out the special tests recommended in IEC 1641 Guide for Testing Under Conditions of Arcing Due to Internal Fault, the result shall be recorded in a test report.
D. Acceptance Tests at Manufacturer’s Work
a) Acceptance tests shall be carried out on the completely assembled switchboards and motor starter panels. Transportable units can be wired together for the purpose of the tests instead of completing the busbar joints.
b) The tests and checks shall include, but not limited to, the following.
c) All the switchboards and motor starter panels shall be visually inspected for technical execution and conformity with the latest issue of approved drawings and the latest issue of the relevant standards. Spot checks shall be made to verify the following:
1) Dimensions
2) The degree of protection of enclosures
3) The degree of protection within compartments
4) The effectiveness and reliability of safety shutters, partitions and shrouds
5) The effectiveness and reliability of operating mechanisms, locks and interlock systems
6) The insulation of the busbar system
7) The creepage distances and clearances
8) The proper mounting of components
9) The internal wiring and cabling system
10) The correct wiring of main and auxiliary circuits
11) The suitability of clamping, earthing and terminating arrangements
12) The correct labeling of functional units
13) The completeness of the data on the nameplate
14) The availability of the earthing system throughout the switchgears
15) The interchangeability of electrically identical components
d) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltage shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac, with a minimum of 1500 Vac for 1 second.
e) Testing of the mechanical and electrical operation of a number of functional units on random basis, including their control and protective devices.
f) CT polarity, magnetization, ratio and burden measurements
g) Secondary injection tests
h) Primary injection tests
i) Painting and finishing tests:
1) Measurement of paint thickness.
2) Humidity (cyclic condensation) tests to BS 3900 Pt. F2. Painted panel shall withstand 1000 hours under test with no blistering of film and corrosion of base metal.
3) Adhesion test to ASTM D3359-02. Test tape shall not expose more than one 3 mm.sq of bare metal or underlying coating.
4) Impact resistance test to BS 3900 Pt. E7. Paint shall not chip off.
j) The manufacturer test shall be verified and witnessed by the Employer’s Representative or his representatives.
E. Site Tests
At the completion of the installation at site, each switchboard and motor starter panels shall be field tested by a representative of the manufacturer. A report recording each item of the tests shall be certified by the manufacturer and submitted to the Employer’s Representative.
a) Visual inspection
1) Correctness of location and mounting
2) Labeling, nameplates and markings.
3) Verification of torque for all nuts and bolts on busway.
4) Observation of cable bracing, both incoming and outgoing, certifying that it is in accordance with the manufacturer’s recommendations.
5) Safety shutters, partitions and shrouds.
6) Functional units, operating mechanisms, locks and interlock systems.
7) Mounting of components.
8) Internal wiring and cabling system.
9) Clamping, earthing and terminating arrangement.
10) Earthing system.
b) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltages shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac with a minimum of 1500V for 1 second.
c) Power frequency withstand voltage test.
d) CT polarity, magnetization, ratio and burden measurements.
e) Secondary injection test
f) Primary injection test
g) Functional / sequence test
i) Operation of each disconnecting means under load
ii) Operation of each automatic transfer switch
iii) Operation of all alarm devices
h) Mechanical operation test
i) Operation of each disconnecting means under load
ii) Operation of each auto transfer switch
iii) Operation of all interlocks
i) Calibration and setting of protection devices
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A. Full type tests
1) Full type tests shall be carried out in accordance with IEC 60439-1, IEC 60947-1, and IEC 60947-6-1. Certificates issued by approved independent testing laboratories shall be submitted to the Employer’s Representative.
The type tests shall include the following:
a) Verification of temperature-rise limits
b) Verification of the dielectric properties
c) Verification of the short-circuit withstand strength
d) Verification of the effectiveness of the prospective circuit
e) Verification of the clearances and creepage distances
f) Verification of mechanical operations
g) Verification of the degree of protection
B. Routine tests
Before the product leaves the works, the manufacturer shall carry out the relevant routine tests in accordance with IEC 60439-1 on the total assembly, and the IEC 60947-1 and IEC 60947-6-1 parts thereof when delivered with time intervals, and the results shall be recorded in a test report.
C. Special tests
Carry out the special tests recommended in IEC 1641 Guide for Testing Under Conditions of Arcing Due to Internal Fault, the result shall be recorded in a test report.
D. Acceptance Tests at Manufacturer’s Work
a) Acceptance tests shall be carried out on the completely assembled switchboards and motor starter panels. Transportable units can be wired together for the purpose of the tests instead of completing the busbar joints.
b) The tests and checks shall include, but not limited to, the following.
c) All the switchboards and motor starter panels shall be visually inspected for technical execution and conformity with the latest issue of approved drawings and the latest issue of the relevant standards. Spot checks shall be made to verify the following:
1) Dimensions
2) The degree of protection of enclosures
3) The degree of protection within compartments
4) The effectiveness and reliability of safety shutters, partitions and shrouds
5) The effectiveness and reliability of operating mechanisms, locks and interlock systems
6) The insulation of the busbar system
7) The creepage distances and clearances
8) The proper mounting of components
9) The internal wiring and cabling system
10) The correct wiring of main and auxiliary circuits
11) The suitability of clamping, earthing and terminating arrangements
12) The correct labeling of functional units
13) The completeness of the data on the nameplate
14) The availability of the earthing system throughout the switchgears
15) The interchangeability of electrically identical components
d) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltage shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac, with a minimum of 1500 Vac for 1 second.
e) Testing of the mechanical and electrical operation of a number of functional units on random basis, including their control and protective devices.
f) CT polarity, magnetization, ratio and burden measurements
g) Secondary injection tests
h) Primary injection tests
i) Painting and finishing tests:
1) Measurement of paint thickness.
2) Humidity (cyclic condensation) tests to BS 3900 Pt. F2. Painted panel shall withstand 1000 hours under test with no blistering of film and corrosion of base metal.
3) Adhesion test to ASTM D3359-02. Test tape shall not expose more than one 3 mm.sq of bare metal or underlying coating.
4) Impact resistance test to BS 3900 Pt. E7. Paint shall not chip off.
j) The manufacturer test shall be verified and witnessed by the Employer’s Representative or his representatives.
E. Site Tests
At the completion of the installation at site, each switchboard and motor starter panels shall be field tested by a representative of the manufacturer. A report recording each item of the tests shall be certified by the manufacturer and submitted to the Employer’s Representative.
a) Visual inspection
1) Correctness of location and mounting
2) Labeling, nameplates and markings.
3) Verification of torque for all nuts and bolts on busway.
4) Observation of cable bracing, both incoming and outgoing, certifying that it is in accordance with the manufacturer’s recommendations.
5) Safety shutters, partitions and shrouds.
6) Functional units, operating mechanisms, locks and interlock systems.
7) Mounting of components.
8) Internal wiring and cabling system.
9) Clamping, earthing and terminating arrangement.
10) Earthing system.
b) Dielectric tests shall be carried out in accordance with IEC 60439-1. The test voltages shall be at least:
1) For main circuits, 2500 Vac for 1 minute.
2) For control and auxiliary circuits, 2 x Un + 1000 Vac with a minimum of 1500V for 1 second.
c) Power frequency withstand voltage test.
d) CT polarity, magnetization, ratio and burden measurements.
e) Secondary injection test
f) Primary injection test
g) Functional / sequence test
i) Operation of each disconnecting means under load
ii) Operation of each automatic transfer switch
iii) Operation of all alarm devices
h) Mechanical operation test
i) Operation of each disconnecting means under load
ii) Operation of each auto transfer switch
iii) Operation of all interlocks
i) Calibration and setting of protection devices
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Friday, November 13, 2009
Electrical switchboard installation
The following is a sample perfomance specifications for the assembly and installation of switchboards in an electrical contract for a new multi-storey office building.
Scope
The scope of this section is to set down briefly the requirements, methods, materials, workmanship, standards and regulations in connection with the complete assembly of switches, starters, and/ or control devices as used in an electrical installation.
Standard of manufacture
The equipment shall comply in every respect with the requirements of the latest edition of B.S. and M.S. specifications and be approved by the Director General, Office of Energy Commission. Switchboards, distribution boards and feeder pillars fabricated by manufacturers unauthorized or unregistered with the Director General, Electricity Supply Board, will not be accepted.
Copies of Type Tested Certificate issued by A.S.T.A. or other approved testing authorities shall be submitted together with the tender.
Electrical system
All switchgear under this section is for use on 415/240 volts, 3 phase 4 wire, 50 Hz alternating current system with solidly earth neutral.
Rupturing capacity
The switchboard shall be capable as a whole of withstanding without damage the electrical, mechanical and thermal stress produced under short circuit conditions, equivalent to 31 MVA at 415 volts for 1 second as defined in BS 5486.
Construction of switchboards
The switchboard shall be modular, cubicle metalclad, self contained, extensible, flush mounted, floor or wall mounted as specified, easily accessible and suitable for housing the individual switchgear and other necessary electrical accessories as specified hereinafter or on the drawings.
The switchboard is to be adequately ventilated and be designed to prevent ingress of all vermin, accidental contact with live parts and to minimize the ingress of dust and dirt. Precaution shall be taken to prevent overheating through hysteresis and eddy current loss.
Extensive labeling and marking shall be used in internally and externally in each switchboard in accordance with the drawings indicating the rating function, designation, number and/ or code letter of the equipment, switches, circuit breakers, fuses, indicating lights etc.
All switchboards must be rested on 100 mm high plinths.
Framework of switchboards
The framework of the switchboard cubicle shall be fabricated from rolled steel angle sections and shall be self-supporting when assembled. The switchboard shall be of rigid construction designed to withstand without any sag, deformation or warping, the loads likely to be experienced during normal operation, maintenance, transportation or maximum fault conditions. All structural members shall be folded on 12 SWG sheet steel. The front door and instrument panels shall be constructed of 12 SWG sheet steel pressed or rolled so that the edges are given a neat round finish. The doors and panels seated on a rubber gasket cemented to the frame. The sides, rear and top panels shall be constructed of 14 SWG sheet steel.
Paint finish and anti corrosion protection
The cubicle framework and sheet steel panels shall be chemically cleaned, degreased and lithoform etched prior electrostatically power sprayed with epoxy paint and oven baked to a touch and smooth finish coating.
All screws, bolts, nuts, washers and similar materials used shall be chromium plated.
Distribution boards
All distribution boards shall be completely enclosed in dust, splash, insect and vermin proof metalclad cubicles and their lids secured with knurled thumb screw. Fuse switches, isolators, contactors, busbar, meters, fuses, or miniature circuit breakers shall be provided as specified on the drawings. Earth terminal blocks, phase barriers, labels and charts for outgoing circuit identification shall be provided.
The distribution boards shall be designed for operation on a 415/ 240 volts, 50 Hz, A.C. system and generally comply with B.S. 214 and suitable for wall, floor or flush mounting as shown on the drawings.
The general construction of frame and panel shall be as specified under clause 5 and 6 but the panels shall be constructed of 16 SWG sheet steel.
The finishing of the metalwork shall be as specified under Clause 7.
The lids shall be designed and installed to ensure that they can be turned through 90 degrees for easy maintenance. All insulating boards provided shall be of hig quality and adequately supported.
Unless otherwise stated, all distribution boards shall be mounted such that their isolating switches are at least 1500 mm above the floor level.
Distribution feeder pillar
Distribution feeder pillar shall be suitable for outdoor service and weather proof type and be equipped with the number of incoming and outgoing circuits as specified in the drawings. It shall be designed with two lockable, hinged doors and removable back panels and provides easy access to cables and terminations.
The general construction of frame and panel shall be as specified under Clause 5 and 6.
The finishing metal work shall be as specified under Clause 7.
All feeder pillars shall be mounted on plinths, which should be at least 460 mm above the ground. They shall be separately earthed and labeled.
Adequate ventilation, insulating phase barriers for connections, cable boxes, end glands for all the incoming and outgoing ways stated in the drawings (including spare ways) shall be provided for each feeder pillar.
The feeder pillars shall be designed to prevent the entry of water during heavy torrential rain. Unless otherwise stated, barriers of railings shall be provided around each feeder pillar to provide some mechanical protection as necessary.
Busbars
Busbars shall be of hard drawn high conductivity electro-tinned copper conductor with rectangular cross section capable to carry continuously the specified current without overheating. They shall be rigidly mounted on non-hygroscopic insulators to withstand any mechanical forces to which they may be subjected under the maximum fault conditions of 31 MVA. The busbars shall be arranged in a horizontal plane and be painted with red, yellow, blue and black colors at appropriate points to distinguish the phases and neutral. Size of neutral busbar shall be of the same as that of the phases.
An earthing busbar of appropriate cross section shall be run at the base of the switchboard.
Air circuit breakers (ACB)
Air circuit breakers shall be of the air break, metalclad, cubicle, horizontal withdrawable and dead front construction of the specified rating and supplied complete with all the necessary instruments, current transformers, trip fuses, trip devices and protective instruments as called for on the accompanying drawings. The breakers shall be suitable for operating on 415 volts 3 phase, 50 Hz, A.C. system and be certified by A.S.T.A. or KEMA for short circuit breaking and making capacity for 31 MVA or lower in accordance with B.S. 4752. The closing mechanism shall be of toggle action trip free type incorporated with mechanical “ON/OFF” and “ISOLATED/ PLUGGED” indicators shall be fitted with manual solenoid operated closing tripping coils allowing remote closing and tripping as specified.
A mechanical trip pushbutton shall be provided and electrical tripping of the circuit shall be accomplished by A.C. trip coils or if shunt D.C. trip coils are offered, a suitable trickle battery charger and nickel cadmium batteries shall be supplied and installed by the contractor.
All trip units are to be current transformer operated and current transformers shall be of suitable ratio, output type and class of accuracy for their function and shall comply in all respects with BS 3938.
Locking facilities shall be provided so that circuit breakers can be prevented from being opened or closed accidentally by means of padlocks, mechanical and electrical lockouts shall be also be provided to prevent closing of the circuit breaker after an over-current trip.
All circuit breakers shall be tested and set to the requirements of the S.O. by approved and licensed testing contractor. The expenses involved in testing the circuit breakers shall be borne by the contractor.
Busbar coupler
Where ACB is used as a coupler, electrical and mechanical interlocks shall be provided for the two incoming ACBs and the coupler cannot be “close” if both the two incoming ACBs are “close”.
Meters
Meters for the external panel mounting shall be of the flush pattern, with square escutcheon plates finished matt black and pressed steel cases. Indicating instruments shall be to B.S. 89 1-st grade, moving iron spring controlled (M.I.S.C) with 100 mm diameter dials (240 deg. Scale) with external zero adjustment, integrating meters shall be to B.S. 37 Parts 1 and 2 and Part 4 with cyclometric registers and protective relays to B.S. 142.
Voltmeters
Each voltmeters shall be of the M.I.S.C. type, be of suitable voltage range to suit the circuit concerned and of a high degree of accuracy. The voltmeter shall be connected in circuit with a 6-position selector switch and protective cutouts fitted with HRC fuse links.
Ammeter
Every ammeter shall be of the M.I.S.C. type, be of suitable range to suit the current rating of the circuit. It is meant to operate through current transformers. It shall have a high degree of accuracy and be connected to three (3) busbar connected current transformers of the correct ratio, burden and class as stated on the relevant schematic diagram. Unless otherwise specified, ammeter shall also be connected in circuit with a 4 position selector switch.
Power factor indicator
Each power factor indicator shall be of the M.I.S.C. type and be suitable for measurement of 3 phase, 4 wire, unbalanced loads through current transformers (for the voltage coil circuit protection, HRC fuse-links shall be used). The indicator shall be scaled to read from 0.5 capacitive to 1 and from 1 to 0.5 inductive circuits.
Frequency meters
Each frequency meter shall be of moving coil type of range 40 cycles to 60 cycles operating in a frequency sensitive rectifier operated bridge network.
Protection relays
Relays shall confirm to BS 142 and shall be heavy-duty pattern, unaffected by vibration or external magnetic fields and be fully tropicalized.
Relay contacts shall be adequately rated and separate contacts shall be provided for alarms and tripping functions.
Relays shall be provided with phase colored flat indicators, which shall be of the hand-reset pattern and shall be capable of being reset without opening the case. Where two or more elements are included in one case, separate indicators shall be provided for each element.
Relays shall be provided with clearly inscribed labels describing their application and rating. Means shall be provided on the relay panels for testing of protective relays and associated circuits.
Overcurrent and earth fault inverse time protection
Relays shall be of the induction disc/ static, inverse time, overcurrent type. Overcurrent elements shall be supplied with adjustable settings for both operating current and time, the adjustment being possible on load. The range of current setting for phase fault elements shall be 50 to 200 % of rated full load with tapping at 25 % intervals and the time setting adjustment shall be 0 to 3 seconds at 10 times the normal operating current. Inverse time earth fault elements shall comply with the foregoing but shall have a range of settings from 10 to 40 % with tapping at 5 % intervals.
Overcurrent relays shall be of time delay induction disc/ electromagnetic type with adjustable setting of 50 % to 200 % of rated full load and adjustable time device shall open the contacts when overcurrent occurs.
Each leakage relays shall be instantaneous/ induction disc type with adjustable setting of 10 to 40 % and connected to the residual circuit of the current transformers accompanied to each phase which shall open the contacts of the circuit breakers when earth leakage occurs up to the allowable limit as set.
Earth leakage circuit breakers
Earth leakage circuit breakers of direct acting type (ELCB) with a tripping sensitivity of 100/ 300 mA to comply with the requirements of Electricity Supply Board and the National Electric Company shall be provided and installed as shown in the Drawings. Every ELCB shall operate successfully for every earth fault in the installation or circuit it controls even with an open circuit in the incoming neutral conductor.
Current transformers
The current transformer for protection, measuring and metering shall comply with B.S. 3938 and shall be of suitable ratio, output, type and class of accuracy for their function as specified in the Drawings. They shall be able to withstand short circuit rupturing capacity of 35 MVA for 1 second without damage.
The current transformers of the ring type shall have appropriate burdens, classes and ratios to suit the installation. Under no circumstances shall the ratio error at zero burden exceed +1 %.
All current transformers shall be mounted to the fixed position of equipment in such a manner that no pressure shall be exerted on their windings and easy access shall be provided for replacement and maintenance of current transformers.
All current transformers shall carry nameplates, identifying types, ratio, class, output and serial number.
Miniature and moulded case circuit breakers (MCCB and MCB)
The miniature and moulded case circuit breakers shall have the continuous ratings as indicated in the drawings at an ambient temperature of 40 degree C. They shall be suitable for use on a 415/240 volts, 50 Hz, A.C. system and the fault current withstand value shall at least be 5 kA for single phase and 10 kA for three phase units installed ot the distribution boards. For installation at switchboards, it shall withstand a fault current of 43 kA.
The circuit breakers shall be quick-make and quick-break type having center toggle mechanism and shall comply with B.S. 3871 part 1 and 2. All breakers shall have inverse time tripping with thermal magnetic trip elements and adjustments for the MCCBs.
All miniature and moulded case circuit breakers supplied shall be of approved manufacture.
At switchboards where MCCBs are used, there shall be facilities for locking out the toggle switch for maintenance.
Fuse switches
All fuse switches shall be of the indoor, metalclad, cubicle, flush or surface mounted, withdrawable and dead front construction type of the specified not less than those shown in the drawings.
They shall be suitable for operation on 415 volts, 3 phase, 4 wire, 50 Hz, A.C. system and be certified for short circuit breaking and making capacity of 31 MVA in accordance with B.S. 3185 and 861.
The switch contacts shall be of the heavy duty, double air break, slow make and quick break pattern with HRC fuse cartridges bolted onto the moving contacts complete with phase barriers, fully shrouded contacts, hard silver plate switch contacts.
The handles shall be fully interlocked and there shall be positive ON/OFF indication on the bodies of the switches. Interlocks shall be provided to prevent the cover fro being open when the switch is on.
Switchfuses
Switchfuses shall be of the number of poles and current ratings as shown on the drawings and shall be of the totally enclosed pattern, metalclad with positive quick make and quick break action.
Switches shall be capable of passing and also interrupting their full rated current safely and without damage. Switch handles shall be interlocked to prevent opening the cover with the switch “ON”.
Fuse shall be of the HRC cartridge type.
Fuses
All fuses supplied shall be HRC type with rating as indicated on the drawings to B.S. 88 or 1382.
All fuses for switches and feeder pillars shall be ‘Class P’ and ‘Class Q” respectively supplied complete with its appropriate carriers as necessary.
Spare fuses amounting to 20 % of the total requirements shall be provided.
Contactors
Contactors provided shall be constructed and rated in accordance with B.S. 775 and the duty classification shall match the load controlled.
All contactors shall be provided with backup protection either in the form of fuses or circuit breakers for interrupting the fault currents.
All contactors provided shall have easily obtainable parts for repair or replacement.
Starters
Starters to be provided under this contract shall meet with the requirements for Electricity Supply Board’s approval and shall be direct-on-line, star-delta, auto transformer or rotor resistance types as to suit the requirements of motor.
They shall be enclosed in a metalclad cover, be provided with the correctly rated contactors, arc chutes and fault current protection such as trip coils or overcurrent coils.
The starters shall be suitable rated to continuously carry the full load current of the motor and also accept the starting current surges without tripping. In this respect, starters shall be fitted with time delays as necessary to prevent tripping when the motors are started.
Unless otherwise specified, all contactors used shall in the starters shall be constructed for heavy-duty operation.
Starters shall have facilities for manual and remote operation and parts shall be easily obtainable for repair, maintenance or replacement.
Isolators
The isolators supplied shall be of the on-load type with single-pole and neutral, triple pole and neutral and double pole and with the rating as indicated on the drawings. Each unit shall be designed and constructed for heavy duty switching and shall carry the rated current continuously without overheating or damage. “ON” and “OFF” indications shall be provided on the body of the switches. Switch handles shall be interlocked to prevent opening the cover when the switch is “ON”.
Metering panel
The metering panel shall be manufactured from anti-rust zinc coated steel plate of not less than 16 SWG with removable hinged front cover to the electricity supply authority’s requirements. Facilities shall be provided on the panel for mounting of the authority’s meters, cutout fuse units and for wiring connection. Finishing shall be in grey enamel.
Working drawings
Prior to manufacturing of any switchboards, distribution boards and feeder pillars, the contractor shall submit complete working drawings to the S.O.’s reprentative for approval.
Packing
The switchboards, distribution boards and feeder pillars shall be factory assembled and tested before delivery to site and of suitable sizes for installation in the situation as shown on the drawings.
Maintenance
The contractor shall also supply:
a. One set of any special tools, gauges and handling appliances at each switchroom required for the normal maintenance of the standard equipment.
b. Sets, as required, of any special tools, gauge or other test equipment required for the assembly, checking or adjustment (but not for normal maintenance) of the standard equipment.
c. A 915 mm wide and 13 mm thick insulation rubber mat running full length in front of the switchboard
d. One set of “as built” wiring diagram in the main switchroom.
Copyright http://electricalinstallationblog.blogspot.com/ -Electrical switchboard installation
Scope
The scope of this section is to set down briefly the requirements, methods, materials, workmanship, standards and regulations in connection with the complete assembly of switches, starters, and/ or control devices as used in an electrical installation.
Standard of manufacture
The equipment shall comply in every respect with the requirements of the latest edition of B.S. and M.S. specifications and be approved by the Director General, Office of Energy Commission. Switchboards, distribution boards and feeder pillars fabricated by manufacturers unauthorized or unregistered with the Director General, Electricity Supply Board, will not be accepted.
Copies of Type Tested Certificate issued by A.S.T.A. or other approved testing authorities shall be submitted together with the tender.
Electrical system
All switchgear under this section is for use on 415/240 volts, 3 phase 4 wire, 50 Hz alternating current system with solidly earth neutral.
Rupturing capacity
The switchboard shall be capable as a whole of withstanding without damage the electrical, mechanical and thermal stress produced under short circuit conditions, equivalent to 31 MVA at 415 volts for 1 second as defined in BS 5486.
Construction of switchboards
The switchboard shall be modular, cubicle metalclad, self contained, extensible, flush mounted, floor or wall mounted as specified, easily accessible and suitable for housing the individual switchgear and other necessary electrical accessories as specified hereinafter or on the drawings.
The switchboard is to be adequately ventilated and be designed to prevent ingress of all vermin, accidental contact with live parts and to minimize the ingress of dust and dirt. Precaution shall be taken to prevent overheating through hysteresis and eddy current loss.
Extensive labeling and marking shall be used in internally and externally in each switchboard in accordance with the drawings indicating the rating function, designation, number and/ or code letter of the equipment, switches, circuit breakers, fuses, indicating lights etc.
All switchboards must be rested on 100 mm high plinths.
Framework of switchboards
The framework of the switchboard cubicle shall be fabricated from rolled steel angle sections and shall be self-supporting when assembled. The switchboard shall be of rigid construction designed to withstand without any sag, deformation or warping, the loads likely to be experienced during normal operation, maintenance, transportation or maximum fault conditions. All structural members shall be folded on 12 SWG sheet steel. The front door and instrument panels shall be constructed of 12 SWG sheet steel pressed or rolled so that the edges are given a neat round finish. The doors and panels seated on a rubber gasket cemented to the frame. The sides, rear and top panels shall be constructed of 14 SWG sheet steel.
Paint finish and anti corrosion protection
The cubicle framework and sheet steel panels shall be chemically cleaned, degreased and lithoform etched prior electrostatically power sprayed with epoxy paint and oven baked to a touch and smooth finish coating.
All screws, bolts, nuts, washers and similar materials used shall be chromium plated.
Distribution boards
All distribution boards shall be completely enclosed in dust, splash, insect and vermin proof metalclad cubicles and their lids secured with knurled thumb screw. Fuse switches, isolators, contactors, busbar, meters, fuses, or miniature circuit breakers shall be provided as specified on the drawings. Earth terminal blocks, phase barriers, labels and charts for outgoing circuit identification shall be provided.
The distribution boards shall be designed for operation on a 415/ 240 volts, 50 Hz, A.C. system and generally comply with B.S. 214 and suitable for wall, floor or flush mounting as shown on the drawings.
The general construction of frame and panel shall be as specified under clause 5 and 6 but the panels shall be constructed of 16 SWG sheet steel.
The finishing of the metalwork shall be as specified under Clause 7.
The lids shall be designed and installed to ensure that they can be turned through 90 degrees for easy maintenance. All insulating boards provided shall be of hig quality and adequately supported.
Unless otherwise stated, all distribution boards shall be mounted such that their isolating switches are at least 1500 mm above the floor level.
Distribution feeder pillar
Distribution feeder pillar shall be suitable for outdoor service and weather proof type and be equipped with the number of incoming and outgoing circuits as specified in the drawings. It shall be designed with two lockable, hinged doors and removable back panels and provides easy access to cables and terminations.
The general construction of frame and panel shall be as specified under Clause 5 and 6.
The finishing metal work shall be as specified under Clause 7.
All feeder pillars shall be mounted on plinths, which should be at least 460 mm above the ground. They shall be separately earthed and labeled.
Adequate ventilation, insulating phase barriers for connections, cable boxes, end glands for all the incoming and outgoing ways stated in the drawings (including spare ways) shall be provided for each feeder pillar.
The feeder pillars shall be designed to prevent the entry of water during heavy torrential rain. Unless otherwise stated, barriers of railings shall be provided around each feeder pillar to provide some mechanical protection as necessary.
Busbars
Busbars shall be of hard drawn high conductivity electro-tinned copper conductor with rectangular cross section capable to carry continuously the specified current without overheating. They shall be rigidly mounted on non-hygroscopic insulators to withstand any mechanical forces to which they may be subjected under the maximum fault conditions of 31 MVA. The busbars shall be arranged in a horizontal plane and be painted with red, yellow, blue and black colors at appropriate points to distinguish the phases and neutral. Size of neutral busbar shall be of the same as that of the phases.
An earthing busbar of appropriate cross section shall be run at the base of the switchboard.
Air circuit breakers (ACB)
Air circuit breakers shall be of the air break, metalclad, cubicle, horizontal withdrawable and dead front construction of the specified rating and supplied complete with all the necessary instruments, current transformers, trip fuses, trip devices and protective instruments as called for on the accompanying drawings. The breakers shall be suitable for operating on 415 volts 3 phase, 50 Hz, A.C. system and be certified by A.S.T.A. or KEMA for short circuit breaking and making capacity for 31 MVA or lower in accordance with B.S. 4752. The closing mechanism shall be of toggle action trip free type incorporated with mechanical “ON/OFF” and “ISOLATED/ PLUGGED” indicators shall be fitted with manual solenoid operated closing tripping coils allowing remote closing and tripping as specified.
A mechanical trip pushbutton shall be provided and electrical tripping of the circuit shall be accomplished by A.C. trip coils or if shunt D.C. trip coils are offered, a suitable trickle battery charger and nickel cadmium batteries shall be supplied and installed by the contractor.
All trip units are to be current transformer operated and current transformers shall be of suitable ratio, output type and class of accuracy for their function and shall comply in all respects with BS 3938.
Locking facilities shall be provided so that circuit breakers can be prevented from being opened or closed accidentally by means of padlocks, mechanical and electrical lockouts shall be also be provided to prevent closing of the circuit breaker after an over-current trip.
All circuit breakers shall be tested and set to the requirements of the S.O. by approved and licensed testing contractor. The expenses involved in testing the circuit breakers shall be borne by the contractor.
Busbar coupler
Where ACB is used as a coupler, electrical and mechanical interlocks shall be provided for the two incoming ACBs and the coupler cannot be “close” if both the two incoming ACBs are “close”.
Meters
Meters for the external panel mounting shall be of the flush pattern, with square escutcheon plates finished matt black and pressed steel cases. Indicating instruments shall be to B.S. 89 1-st grade, moving iron spring controlled (M.I.S.C) with 100 mm diameter dials (240 deg. Scale) with external zero adjustment, integrating meters shall be to B.S. 37 Parts 1 and 2 and Part 4 with cyclometric registers and protective relays to B.S. 142.
Voltmeters
Each voltmeters shall be of the M.I.S.C. type, be of suitable voltage range to suit the circuit concerned and of a high degree of accuracy. The voltmeter shall be connected in circuit with a 6-position selector switch and protective cutouts fitted with HRC fuse links.
Ammeter
Every ammeter shall be of the M.I.S.C. type, be of suitable range to suit the current rating of the circuit. It is meant to operate through current transformers. It shall have a high degree of accuracy and be connected to three (3) busbar connected current transformers of the correct ratio, burden and class as stated on the relevant schematic diagram. Unless otherwise specified, ammeter shall also be connected in circuit with a 4 position selector switch.
Power factor indicator
Each power factor indicator shall be of the M.I.S.C. type and be suitable for measurement of 3 phase, 4 wire, unbalanced loads through current transformers (for the voltage coil circuit protection, HRC fuse-links shall be used). The indicator shall be scaled to read from 0.5 capacitive to 1 and from 1 to 0.5 inductive circuits.
Frequency meters
Each frequency meter shall be of moving coil type of range 40 cycles to 60 cycles operating in a frequency sensitive rectifier operated bridge network.
Protection relays
Relays shall confirm to BS 142 and shall be heavy-duty pattern, unaffected by vibration or external magnetic fields and be fully tropicalized.
Relay contacts shall be adequately rated and separate contacts shall be provided for alarms and tripping functions.
Relays shall be provided with phase colored flat indicators, which shall be of the hand-reset pattern and shall be capable of being reset without opening the case. Where two or more elements are included in one case, separate indicators shall be provided for each element.
Relays shall be provided with clearly inscribed labels describing their application and rating. Means shall be provided on the relay panels for testing of protective relays and associated circuits.
Overcurrent and earth fault inverse time protection
Relays shall be of the induction disc/ static, inverse time, overcurrent type. Overcurrent elements shall be supplied with adjustable settings for both operating current and time, the adjustment being possible on load. The range of current setting for phase fault elements shall be 50 to 200 % of rated full load with tapping at 25 % intervals and the time setting adjustment shall be 0 to 3 seconds at 10 times the normal operating current. Inverse time earth fault elements shall comply with the foregoing but shall have a range of settings from 10 to 40 % with tapping at 5 % intervals.
Overcurrent relays shall be of time delay induction disc/ electromagnetic type with adjustable setting of 50 % to 200 % of rated full load and adjustable time device shall open the contacts when overcurrent occurs.
Each leakage relays shall be instantaneous/ induction disc type with adjustable setting of 10 to 40 % and connected to the residual circuit of the current transformers accompanied to each phase which shall open the contacts of the circuit breakers when earth leakage occurs up to the allowable limit as set.
Earth leakage circuit breakers
Earth leakage circuit breakers of direct acting type (ELCB) with a tripping sensitivity of 100/ 300 mA to comply with the requirements of Electricity Supply Board and the National Electric Company shall be provided and installed as shown in the Drawings. Every ELCB shall operate successfully for every earth fault in the installation or circuit it controls even with an open circuit in the incoming neutral conductor.
Current transformers
The current transformer for protection, measuring and metering shall comply with B.S. 3938 and shall be of suitable ratio, output, type and class of accuracy for their function as specified in the Drawings. They shall be able to withstand short circuit rupturing capacity of 35 MVA for 1 second without damage.
The current transformers of the ring type shall have appropriate burdens, classes and ratios to suit the installation. Under no circumstances shall the ratio error at zero burden exceed +1 %.
All current transformers shall be mounted to the fixed position of equipment in such a manner that no pressure shall be exerted on their windings and easy access shall be provided for replacement and maintenance of current transformers.
All current transformers shall carry nameplates, identifying types, ratio, class, output and serial number.
Miniature and moulded case circuit breakers (MCCB and MCB)
The miniature and moulded case circuit breakers shall have the continuous ratings as indicated in the drawings at an ambient temperature of 40 degree C. They shall be suitable for use on a 415/240 volts, 50 Hz, A.C. system and the fault current withstand value shall at least be 5 kA for single phase and 10 kA for three phase units installed ot the distribution boards. For installation at switchboards, it shall withstand a fault current of 43 kA.
The circuit breakers shall be quick-make and quick-break type having center toggle mechanism and shall comply with B.S. 3871 part 1 and 2. All breakers shall have inverse time tripping with thermal magnetic trip elements and adjustments for the MCCBs.
All miniature and moulded case circuit breakers supplied shall be of approved manufacture.
At switchboards where MCCBs are used, there shall be facilities for locking out the toggle switch for maintenance.
Fuse switches
All fuse switches shall be of the indoor, metalclad, cubicle, flush or surface mounted, withdrawable and dead front construction type of the specified not less than those shown in the drawings.
They shall be suitable for operation on 415 volts, 3 phase, 4 wire, 50 Hz, A.C. system and be certified for short circuit breaking and making capacity of 31 MVA in accordance with B.S. 3185 and 861.
The switch contacts shall be of the heavy duty, double air break, slow make and quick break pattern with HRC fuse cartridges bolted onto the moving contacts complete with phase barriers, fully shrouded contacts, hard silver plate switch contacts.
The handles shall be fully interlocked and there shall be positive ON/OFF indication on the bodies of the switches. Interlocks shall be provided to prevent the cover fro being open when the switch is on.
Switchfuses
Switchfuses shall be of the number of poles and current ratings as shown on the drawings and shall be of the totally enclosed pattern, metalclad with positive quick make and quick break action.
Switches shall be capable of passing and also interrupting their full rated current safely and without damage. Switch handles shall be interlocked to prevent opening the cover with the switch “ON”.
Fuse shall be of the HRC cartridge type.
Fuses
All fuses supplied shall be HRC type with rating as indicated on the drawings to B.S. 88 or 1382.
All fuses for switches and feeder pillars shall be ‘Class P’ and ‘Class Q” respectively supplied complete with its appropriate carriers as necessary.
Spare fuses amounting to 20 % of the total requirements shall be provided.
Contactors
Contactors provided shall be constructed and rated in accordance with B.S. 775 and the duty classification shall match the load controlled.
All contactors shall be provided with backup protection either in the form of fuses or circuit breakers for interrupting the fault currents.
All contactors provided shall have easily obtainable parts for repair or replacement.
Starters
Starters to be provided under this contract shall meet with the requirements for Electricity Supply Board’s approval and shall be direct-on-line, star-delta, auto transformer or rotor resistance types as to suit the requirements of motor.
They shall be enclosed in a metalclad cover, be provided with the correctly rated contactors, arc chutes and fault current protection such as trip coils or overcurrent coils.
The starters shall be suitable rated to continuously carry the full load current of the motor and also accept the starting current surges without tripping. In this respect, starters shall be fitted with time delays as necessary to prevent tripping when the motors are started.
Unless otherwise specified, all contactors used shall in the starters shall be constructed for heavy-duty operation.
Starters shall have facilities for manual and remote operation and parts shall be easily obtainable for repair, maintenance or replacement.
Isolators
The isolators supplied shall be of the on-load type with single-pole and neutral, triple pole and neutral and double pole and with the rating as indicated on the drawings. Each unit shall be designed and constructed for heavy duty switching and shall carry the rated current continuously without overheating or damage. “ON” and “OFF” indications shall be provided on the body of the switches. Switch handles shall be interlocked to prevent opening the cover when the switch is “ON”.
Metering panel
The metering panel shall be manufactured from anti-rust zinc coated steel plate of not less than 16 SWG with removable hinged front cover to the electricity supply authority’s requirements. Facilities shall be provided on the panel for mounting of the authority’s meters, cutout fuse units and for wiring connection. Finishing shall be in grey enamel.
Working drawings
Prior to manufacturing of any switchboards, distribution boards and feeder pillars, the contractor shall submit complete working drawings to the S.O.’s reprentative for approval.
Packing
The switchboards, distribution boards and feeder pillars shall be factory assembled and tested before delivery to site and of suitable sizes for installation in the situation as shown on the drawings.
Maintenance
The contractor shall also supply:
a. One set of any special tools, gauges and handling appliances at each switchroom required for the normal maintenance of the standard equipment.
b. Sets, as required, of any special tools, gauge or other test equipment required for the assembly, checking or adjustment (but not for normal maintenance) of the standard equipment.
c. A 915 mm wide and 13 mm thick insulation rubber mat running full length in front of the switchboard
d. One set of “as built” wiring diagram in the main switchroom.
Copyright http://electricalinstallationblog.blogspot.com/ -Electrical switchboard installation
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