Transformer Secondary - 2nd opinion...and 3rd, 4th......

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emahler

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Here is the setup....all equipment is in one room...an open storage room. Clearances are not an issue...

MDP - 80A 3PH 480V cb feeds a 75kVa 480-120/208V transformer. Length of run is approximately 12 feet.

transformer feeds a 225A MLO panel. Run is 6' from transformer to lugs. Wire is 3/0.

The 225A panel feeds a UPS through a 100A 2P cb. Additional circuits out of here are 2- 2P 40A to feed air handlers in the UPS, 2- 3P 15A to feed A/C condensers for the UPS, 2- 1P 20A to feed other equipment for the UPS...so for those keeping score, that's 7 means of disconnect in this panel.

now the question - is a MCB required in the 225A panel?
 
Emaler, your secondary conductors need protection per 240.21 and your panel board needs protection per 408.36. Also if your going to need the ful 225 amps, your conductors are only rated for 200 amps.
Rick
 
As RUWired said, the issue is with the conductor protection requirements of 240.21(C), the tap rules.

Your installation does not meet any of the exceptions. 6 circuits is not the real problem.

Several code cycles back this was a common installation.
 
This is not a Service, it is a Separately Derived System.
As RUWired mentioned, the Panelboard Overcurrent Protection is required by 408.36(B), which takes you to 240.21(C)(1).
Check 250.30 for proper grounding of a Separately Derived System, too.
Your Primary breaker could be higher, too - Full Load Amps at 480 = 91.
What size UPS?
db
 
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