Size wire/conduit for transformer/machine - Electrician Talk - Professional Electrical Contractors Forum

firefighter4135 · 05-18-2008, 09:14 PM

I have a partner that has sized wire and conduit for a machine installation. He had some questions and I am trying to help him get some answers that I am not sure about 100%........
Coming from a bus duct 480VAC to a 3 kva transformer to a robot control panel with a FLA of 40A. / 200 VAC
Is this a correct size transformer??
We did the calculations and we came up with approx. 13 kva....Sized to a 16 kva transformer instead of a 3 kva. Are we correct or is the 3 kva correct?......Thank you!!!

nap · 05-18-2008, 09:21 PM

single phase or 3 phase?

I suspect 3 phase but...

firefighter4135 · 05-18-2008, 09:26 PM

I am sorry.......Bus duct 480 VAC 3ph to a 3 kva transformer to a robot control panel 200 VAC 3ph/ FLA of 40A.

nap · 05-19-2008, 07:13 PM

looks like a 14 kVA rating.

here is a couple calculators:

http://www.csgnetwork.com/xformercalc.html

http://www.t-r.com/TransformerCalculator.aspx

firefighter4135 · 05-20-2008, 04:15 PM

Thank you for the reply. That is what we came up with(13.something) We installed a 16kva and resized the wire that they wanted run. Thank you for the second oppinion.

ThatRick · 06-20-2011, 11:50 PM

Yep that is it. Simple math. Amps times Volts times the square root of 3 (1.732) divided by 1000. You need the weird number anytime you convert between 2 phase and 3 phase.