Emergency circuits in MCC

[M. Ryan]

I'm looking for a code article that addresses refeeding a drawer within an MCC from a seperate EM circuit.

My concern is safety, you could LOTO the main MCC disconnect and assume all drawers are off and safe to work on when in fact one is still energized from the alternate EM circuit.

I thought the NEC clearly addressed this issue, haven't found it yet. Maybe someone has better NEC tabs or more patience than me.

Thanks,
Ryan

 

[petersonra]

would this not be addressed in the required written lockout procedure?

perhaps a sign on the bucket that has alternate power fed to it.

I can't say i have ever seen this done.

having said that, it would appear to violate the basic definition of an MCC.

Motor Control Center. An assembly of one or more enclosed
sections having a common power bus and principally
containing motor control units.

However, I do not recall any prohibition on having a second power source to an MCC.

It does seem like an odd thing to do though.

 

[jim dungar]

Multiple power sources to a single piece of equipment are not prohibited by the NEC.

Individual buckets of an MCC not being controlled by the main disconnect, are not uncommon. Operational issues like proper documentation (e.g. one-lines) and signage (e.g. 'fed from separate cource') are typically better addressed by NFPA70E and OSHA rather than by an installation document like the NEC.

 

[M. Ryan]

Guys,

Thanks for the comments, I will thumb thru NFPA70E, and see what I can turn up.

Ryan