480V single phase lighing on 3 phase breaker 1

[FlaBouy]

Hi guys, new member here. Can someone explain how one figures breaker size/fixture quantity for 480V single phase 1000W metal halide fixtures on a three phase feeder utilizing a 3 pole contactor fed with a 3 pole 480V breaker. Switching is via 120V control. I understand balancing single phase loads (A,B... B,C... A,C) to the contactor, just a little confused at how you determine maximum amount of 1000W fixture on a 30A breaker.

I assume that at 2.4A per fixture I am allowed 10 fixtures per single phase circuit to meet a single phase continuous load (30A x .8 = 24A)But say this is a three phase breaker/contactor... How do you calculate that same 30A circuit...

Thanks

 

[alehman]

If you connect three 2.4A fixtures A-B, B-C and C-A on a three-phase source, the line current will be 2.4*sqrt(3).

 

[FlaBouy]

So I am to assume that 15 2.4A fixtures comnnected A-B, B-C, C-A on a three phase source would be 12A * sqrt(3)? being as balanced loads would be 5 sets 2.4A * 1.732 or 20.8A?

 

[alehman]

That sounds about right.