Panel Load Info

[jaswild]

First, I've done EE design work before, but it's been awhile and it was all experience based, I don't have a degree. So there are a couple things I've forgotten about loading a panel which I was asked to do recently on a computer job.

I have a 150A, 120/208V., 3P, 4W panel, which I've made a load chart for to determine the load on the panel.

First question - there are breakers in the panel that both connect to a single pole, but have an A & B connection per the diagram in the panel board cover, and there are dual 20 pole breakers, do I treat this as a 40/1 pole load? Therefore putting a 3840VA 80% max load on the B leg of the Y?

Second, once I've determined the VA load on each phase, what is the finishing calculation? When I previously worked as a designer, there were existing numbers for this, but I don't remember the calculation for coming up with it from scratch. So if I add the 3 phases together and have 44860VA total load on the panel, how many amps is that in design being used?

I apologize if these are simple questions, but I'm at a loss and just need to finish this simple task.

Thank you.

Jason

 

[jaswild]

Ok, I think I've managed to answer my Second question after doing a little hunting. 44860 / [208 * sqrt(3)] = 125A. So I guess this panel is overloaded per code, 80% load is 120A.

I still am unsure what to do about my first question, if someone could please answer that one?

Thanks.

 

[davidbeach]

Load must go on the pole (phase) it is connected to. So if you have tandem breakers that connect two loads to the same phase, sum both loads on that phase. If you have two pole breakers, half the load goes on each phase.

 

[jaswild]

Thanks David.