# single-phase loads on 3-phase circuit

Discussion in 'The Projects Forum' started by gummo, Jan 21, 2009.

1. ### gummo Thread Starter New Member

Jan 21, 2009
2
0
I am working on designing a power distribution panel that will supply power to UV lamp ballasts. The power coming into the distribution panel is 240VAC 3-phase. Suppose I have three single-phase loads (where the load is an arrangement of ballasts), each 48 Amps. If the three loads are balanced (one load across phase a-b, one load across a-c, and one load across b-c), will the full-load amps of the power distribution panel be 48 Amps? I will need to put this value on a label and attach it to the panel (per UL and NEC), and also need to know so I can size the main circuit breaker (which I know how to do if I can determine the FLA).

Upstream of the panel, there is a 480/240VAC 3-phase transformer. Not sure if it is delta or wye connected, or if it even makes a difference. Someone was telling me that I need to multiply the 48 Amps by the square root of 3 to get the FLA.

Does anyone have any answers or insight on the above? Any help would be very much appreciated. Thank you.

2. ### thingmaker3 Retired Moderator

May 16, 2005
5,073
8
Please check again. Is the transformer 240V open delta, or is it 277/480 Wye?
This may aid your understanding: http://mysite.du.edu/~jcalvert/tech/threeph.htm

3. ### gummo Thread Starter New Member

Jan 21, 2009
2
0
Thanks for your help. I understand it better now. The transformer doesn't matter. It didn't occur to me at first that connecting single phase loads across the lines turns out to be a delta connected load. It makes more sense now.