NATIONAL ALUMINIUM COMPANY LIMITED - Rites

Incomer and bus coupler panels
MCC incomers and bus couplers shall have Air circuit breakers. Incomers and bus couplers
shall be rated for at least 125% of maximum de demand mand taking into account the spare feeders
and shall be suitable for the specified fault level.
Incomers and bus coupler shall be electrically interlocked to prevent parallel operation.
However, a definite delay defeat Interlock switch shall be provided to facilitate parallel
operation. Auto changeover facility shall also be provided between the two incomers and bus
coupler.
Feeder Modules
Feeders for motors of 75 kW and above shall be fully drawout type air circuit breakers (ACBs)
with numeric type comprehensive mprehensive motor protection relays. Other motor feeders shall be
consisting of MCCB, contactor, overload relay as main power components to ensure type 2
protection. The short circuit release of MCCBs shall be suitably selected to the applications
concerned.
At least 10% spare feeders (minimum one spare feeder of each type and rating bus sectionwise)
shall be provided. Ammeters with selector switches shall be provided for all continuous /
intermittent running motors beyond 15 kW rated drives.
Busbars and d terminations
Busbars and connection shall be of high conductivity aluminium/aluminium alloy of suitable
hardness and purity complying with as per IS IS-5082-1981. 1981. Busbars shall be insulated by colour
coded heat shrinkable sleeves.
Busbars shall be rated for the nominal current rating of incoming breaker and for the full
short-circuit circuit rating. Earth bus shall run throughout the length of MCC at bottom .
Control bus shall be provided in the bus bar chamber isolated with main bus in all the MCCs.
Similarly power and control terminations shall be in separate chambers in the MCCs. Cable
alley y shall have sufficient space for maintenance and minimum width of cable all alley shall be
300 mm. Shrouding/isolation shall be provided for outgoing power terminations in th the cable
alleys. ys. Modules of MCCs shall be spacious for easy maintenance of the various equipment
inside.
Short circuit strength
Rated short time withstand current shall not be less than 50 kA for 1 second. Rated peak
withstand current not less than 2.1 times the specified short circuit level.
Air circuit breaker (ACB)
Technical Specification:Sec-6, Electrical
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