Low voltage switch racks

[joshtrevino]

Does the NEC address requirements (bus rating, main disconnect, etc) specifically for free standing low voltage (480v) switch racks. Specifically, I am desiging a switch rack with a main bus enclosure, main breaker, two size four starter enclosures, and spare capacity for future.

Please state specific articles if applicable. Thanks.

 

[petersonra]

Does the NEC address requirements (bus rating, main disconnect, etc) specifically for free standing low voltage (480v) switch racks. Specifically, I am desiging a switch rack with a main bus enclosure, main breaker, two size four starter enclosures, and spare capacity for future.

Please state specific articles if applicable. Thanks.

Pretty much these are all design considerations and not code driven.

You can make the bus any size you want as long as it can handle the current it will see. Same with the main disconnect. In fact, you may not even need a main on it by code.

 

[joshtrevino]

Pretty much these are all design considerations and not code driven.

You can make the bus any size you want as long as it can handle the current it will see. Same with the main disconnect. In fact, you may not even need a main on it by code.

Bob,
What is the determining factor for whether or not a main is needed? Specific NEC article?

 

[petersonra]

Bob,
What is the determining factor for whether or not a main is needed? Specific NEC article?

it is mostly a design choice. as long as the bus is properly protected in some way there is no real need for a main. you can protect the bus at the point it is fed from if you want.

however, there may be some cases where it is very handy to have a main, such as where it is fed from the secondary of a transformer. you have to protect the xfmr secondary and those conductors, so a main is often a cost effective way to handle that.

you might also sometimes find a main is useful if you need a disconnecting means by code, such as a feeder from another building.

 

[petersonra]

incidentally, I would question whether this is a place where a switch rack of some sort is overkill.