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Old 04-08-2020, 06:38 AM   #1
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Question MCC Room Requirements

I work at a sawmill and recently we has a steam turbine installed here to supplement power from our boiler house. The turbine output is rated for 575 volts and runs around 513 KW. The electrical equipment is in a room with questionable clearance and the construction of the room is not what I would typically see in an electrical equipment or MCC room. They basically built a couple walls and a ceiling from 2x4's and double 5/8" sheetrock. I have tried to find in the code book what the specific requirements are for this room as any I've ever worked in were steel and concrete. Any info is appreciated.
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Old 04-08-2020, 06:58 AM   #2
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In a sawmill? Just be glad you actually have a room to put the MCC in.

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Old 04-08-2020, 08:58 AM   #3
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The actual room construction would be determined by local building codes. The electrical installation clearances and ingress/ egress would be determined by NEC article 110.

There are some specific NEC requirements if there are transformers located in this space. See article 450.

Last edited by varmit; 04-08-2020 at 09:03 AM.
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Old 04-09-2020, 02:01 PM   #4
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The only thing that changes is the clearance distances when doors are open (table 110.26) based on conductivity of the wall material. Sheetrock is considered non-conductive, concrete IS considered conductive. I have, on a couple of occasions, added Sheetrock to a wall (one concrete, one corrugated steel) in order to decrease the clearances required.

The only other requirement is that MCCs are all rated for a maximum of 40C (104F) operation so the room must have adequate ventilation and/or air conditioning to be able to maintain that when everything is running. I have walked into some MCC rooms where the heat blast makes me swoon, then the users are complaining that their VFDs are continually failing "for no reason".
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