Article 590.

[Dale001289]

Construction needs 480V temporary construction power. They want 3-100A three phase feeders to a new unit under construction. An existing MCC contains the required circuit breakers, but the upstream 1000kVA power transformer that feeds the MCC main circuit breaker is out of service. Construction wants to 'back-feed 'the MCC via a 400A branch circuit breaker in one of the vertical sections from another nearby power transformer secondary that is lightly loaded. Is this permissible for temporary power under NEC?

 

[zbang]

If nothing else, there's a lot of lockout/tagouts in your future- I'd lockout or isolate pretty much everything that isn't the 400a "in" and the three 100a "outs".

 

[Smart $]

... An existing MCC contains the required circuit breakers, ...

Do those circuit breakers power three existing 100A feeders to the construction area and are the permanent feeders, or are they just looking at using the 400A in, busing, and 3x100A out... and the rest will all be temp'd into and out of the MCC?

 

[Dale001289]

Do those circuit breakers power three existing 100A feeders to the construction area and are the permanent feeders, or are they just looking at using the 400A in, busing, and 3x100A out... and the rest will all be temp'd into and out of the MCC?

These will be used for temporary ONLY both in/out. What about signage? What about the arc-fault energy and short circuit current availability? Do you think I'll need current limiters on the temp transformer backfeeding the 400A CB?

Do you think it needs to be reviewed by a PE for Arc-flash??

Thanks in advance guys.

Dale

 

[Smart $]

These will be used for temporary ONLY both in/out. What about signage? What about the arc-fault energy and short circuit current availability? Do you think I'll need current limiters on the temp transformer backfeeding the 400A CB?

Do you think it needs to be reviewed by a PE for Arc-flash??

Thanks in advance guys.

Dale

Consider...

590.2 All Wiring Installations.
(A) Other Articles. Except as specifically modified in this
article, all other requirements of this Code for permanent
wiring shall apply to temporary wiring installations.
(B) Approval. Temporary wiring methods shall be acceptable
only if approved based on the conditions of use and
any special requirements of the temporary installation.

 

[Dale001289]

Consider...

thanks for the feedback!