600V Bus Rated MCC Used for 208V Not Configurable for 480V

[MorrisMJ]

I am working on a project where a client has an MCC which shows a rating of 600V on the nameplate. The MCC is being used for 208V service right now, and the client wants to switch over to 480V service for the utilization equipment. The MCC is relatively new, and I would like to reuse it.

I am hearing that using this particular MCC for 480V service would void the UL listing. I am thinking that it must be the control wiring and transformers not being rated for 480V service, since the bus rating is posted as 600V. This seems strange, since the amount of money saved on the equipment would be relatively low in my opinion.

Does anyone have any ideas as to why this would be the case?

 

[jraef]

MCCs are only rated based on the maximum voltage, not a specific voltage. So you can use a 600V rated MCC for anything 600V and below, as far as the structure is concerned. But you are correct in that if it is being used on 208V now, and there are CPTs in each starter bucket, those CPTs will need to be changed. It's also possible however that being that it was 208V and 120V was available without a CPT by going phase to neutral, that your buckets now do not have CPTs at all, you should look. If not, you can just leave it the same, but bring in a separate source of 120V for control power to each bucket, though an aux contact on the disconnect handle and a fuse.

Pay attention to your fault current bracing of the MCC, because it must meet or exceed the available fault current in your new 480V system.


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