Question? I have a 1600amp 480vac 3ph MCC feeding multiple motors with maximum loading of 600 amps when all are running. We want to add seven more buckets of 7 amps per bucket (small motors) but do not have space for them. The end section of MCC is a tap section to add on to buss. The question is do we have to size cable for the 1600amp feed or can we size cable at the 125amp main disconnect size of additional MCC sections. The additional section is in same room across isle from 1600amp main disconnect.
MCC feed thru
- Thread starter dunk76
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MCC tap
MCC tap
I would think this would fall under the rules of NEC 240.21 and I don't believe the "tap" you describe would be legal under any of the tap rules listed.
If your "taps" were rated at 533 amps (1/3 of the breaker ampacity) and your distance is 25' or less, 240.21 (B) 2 would apply, IMHO, although a standard 125 amp breaker would not have lugs to accomdate the tap conductors.
Although commonplace, tapping the MCC buss might be viewed as questionable under the alteration of listed equipment. Perhaps you can get a "subfeed" breaker that will fit the MCC.
MCC tap
I would think this would fall under the rules of NEC 240.21 and I don't believe the "tap" you describe would be legal under any of the tap rules listed.
If your "taps" were rated at 533 amps (1/3 of the breaker ampacity) and your distance is 25' or less, 240.21 (B) 2 would apply, IMHO, although a standard 125 amp breaker would not have lugs to accomdate the tap conductors.
Although commonplace, tapping the MCC buss might be viewed as questionable under the alteration of listed equipment. Perhaps you can get a "subfeed" breaker that will fit the MCC.
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jcormack
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What is the length of your tap connection? If it falls within guidelines of 240 you can size for your smaller main, but I think poster above is correct, at least 1/3 ampacity.
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