How to size a transformer/panel

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Nietz001

Member
Location
St Paul MN
I have a 112.5 kva dry type transformer. At 208, 3 phase volts I calculate it will produce 312 volts on the secondary. Can I install a 400 amp MCB anp panel?
 

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
Short answer, "Yes."

Longer answer, "You meant '312 amps on the secondary,' and when you multiply that by 125%, and round up to the next higher standard overcurrent rating, you end up with 400 amps."
 

iwire

Moderator
Staff member
Location
Massachusetts
I'm lazy, can you give me the NEC reference so I don't have to find this.....:ashamed1:

But I was felling lazy .... :D


Here you go, no problem.



240.21(C) Transformer Secondary Conductors. A set of conductors
feeding a single load, or each set of conductors
feeding separate loads, shall be permitted to be connected
to a transformer secondary, without overcurrent protection
at the secondary, as specified in 240.21(C)(1) through
(C)(6). The provisions of 240.4(B) shall not be permitted
for transformer secondary conductors.

You would have to look at 240.21(C)(1) through (C)(6) for additional details.
 
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