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So I'll attach a copy of a pic I took. Might be a little hard to see. Basically they're asking for the wire size feeding three 25kva 600 120/240 delta-wye transformers. They added up all the kva 75000kva÷1038=72.2 and then they multiplied by 1.25 to get 90amps which I don't get. In rule 26-256 1) b) it states the sum of the rated primary currents plus 25% of the largest transformers primary current for a group of transformers operated in parallel OR on a common feeder. So wouldn't it be 75000kva÷1038= 72amps and 25000÷1038= 24amps×.25= 6amps. 72+6= 78amps then on table 2 on the 75 degree colomn it would be 4awg?
20210504_194357.jpg
 

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So I'll attach a copy of a pic I took. Might be a little hard to see. Basically they're asking for the wire size feeding three 25kva 600 120/240 delta-wye transformers. They added up all the kva 75000kva÷1038=72.2 and then they multiplied by 1.25 to get 90amps which I don't get. In rule 26-256 1) b) it states the sum of the rated primary currents plus 25% of the largest transformers primary current for a group of transformers operated in parallel OR on a common feeder. So wouldn't it be 75000kva÷1038= 72amps and 25000÷1038= 24amps×.25= 6amps. 72+6= 78amps then on table 2 on the 75 degree colomn it would be 4awg?
View attachment 155789
This is not about three transformers fed with one source, it’s three single phase transformers wired into a bank to make one 3 phase transformer
 
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