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Re: 3Phase 300KVA Transformer

I have a hard time understanding your descriptions and your questions, but I'll give it a try.

Originally posted by eeee:

** Is there something I am missing here? A 33 amp load draw from a large manufacturing building as determined by the consulting firm in their load study?? **
I'll start there. It sounds like they are talking about load on the primary side of the transformer. 33 amps times 12,460 volts times 1.732 equals 712 KVA. 20 amps times 12,460 volts times 1.732 equals 431 KVA.

Originally posted by eeee:

** 208/120Volt wye-wye connected transformers per building. **
Why a wye-wye? It is far more common to use Delta-Wye.

Originally posted by eeee:

** I calculate 278 amps capacity for the secondary for both transformers: 100,000VA/(1.73*208Volts)=278 amps. **
The transformer is connected as a bank of three single phase units. You must calculate the secondary current in the three-phase configuration. That means you use three times the 100 KVA of a single unit. 300,000 VA divided by (1.732 * 208) equals 832 amps.

Originally posted by eeee:

**. . . the demand current draws for each loaded circuit add in parallel. **
I have no idea what you meant by that.

Charles E. Beck, P.E., Seattle

Comments based on 2008 NEC unless otherwise noted.

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