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Tuesday, March 29, 2016

Question:

We have an old building with a GE QMQR fused switchboard.  The Fuses switch will be 200 amp with RK5 fuses.  The voltage is 208/120, 3 phase 4 wire.  We’re installing a new 200 amp panelboard, which is 300 feet from the SWBD. Does the panelboard have to be MCB or can it be MLO?  What are the code articles that would apply?

If it has to be MCB, would the AIC rating of this device need to be at a minimum?

Thanks, Mike B.

A

Answer:

Hey Mike thanks for your question. Panelboards must have overcurrent protection that is not more than the panelboard rating. The protection can be in the panelboard as a main or on the supply side as stated in 408.36. Whether you use fuses in the switchboard or a main circuit breaker in the panelboard is your choice, but they need to have an interrupting rating that is at least equal to the fault current as stated in 110.9. The panelboard also needs to have a short circuit current rating suitable for the fault current as stated in 110.10.

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