help I've slept awhile and have lost my calc book???

[rt66electric]

please help !! I have slept over 15 years since I have done these calculations, and I have misplaced my ugly book.. what size KVA transformer does my friend need to::

Xfmr up from 240 wildleg to 480-3p for a machine w/ 70 amp draw???

also the size for the 240v side breaker.???

 

[chris kennedy]

20kw on a 90A breaker.

 

[rt66electric]

I got 58 kva and 140 amps@240 ???/

I got 58 kva and 140 amps@240 ???/

I found a formula ina G.E. xfmr book KVA = ( (volts)x(amps)x(1.732)) / 1000


58.2 KVA = ((480)x(70)x(1.732)) / 1000

What am doing wrong ???


58.2KVA = ((240)x( ? )x(1.732)) /1000

? = 140 amps @ 240


Dang I wish I could find my OLD apprentice schools books. I think my wife(threw out) replaced them with decor.

 

[chris kennedy]

That was off the top of my head, stand by for my calcs.

 

[chris kennedy]

I found a formula ina G.E. xfmr book KVA = ( (volts)x(amps)x(1.732)) / 1000


58.2 KVA = ((480)x(70)x(1.732)) / 1000

What am doing wrong ???


58.2KVA = ((240)x( ? )x(1.732)) /1000

? = 140 amps @ 240

Actually, this is what I get also. Sorry for winging it.:roll:

Dang I wish I could find my OLD apprentice schools books. I think my wife(threw out) replaced them with decor.

Throw out 15 pairs of her shoes and 2 of her purses, that should get her attention.

 

[rt66electric]

thanks

thanks

Thanks for the double check--DENNIS