Power Per Phase for 2Pole circuit

[jobrafo]

The NEC gives a %tolerance that each phase can be out by. I'm quite sure that it's 10% OR LESS?? Given that, how do you determine the KVA on each phase.
208v * 40a = 8.32KVA. 40amp breaker 2pole is required.

I'm designing a power panel. In it I am showing that each phase of the system is balanced. To do that, the watts or kva on each phase have to be known in order to this. I really know no other way of referring to the amount of Power that can be measured on a Phase. If you can measure the voltage on a phase and measure the current on a phase, then in essence, you have the power being generated, consumed, and transmitted across any given phase.
How else can you show a balanced (phase to phase) system when using 2pole circuits?

[ April 02, 2003, 02:16 PM: Message edited by: jobrafo ]

 

[charlie b]

Re: Power Per Phase for 2Pole circuit

I think that your answer is in the following process (working here with a 3-phase, 120/208V panel):
(1) Take the voltage being supplied to the load. If it is a line-to-neutral, the voltage would be 120. If it is a line-to-line (i.e., 2-pole), it is 208V. If is it a 3-phase load, it is also 208V.
(2) Take the current drawn by the load (not the current rating of the breaker)
(3) Multiply these two figures. For a 3-phase load, you also multiply by 1.732 (i.e., the square root of 3).
(4) Divide by 1000, to covert to kva.
(5) For a single phase, single-pole, 120V load, assign that kva to the phase to which the load is connected.
(6) For a single phase, 2-pole, 208V load, assign half that kva to each of the two phases to which the load is connected.
(7) For a 3-phase load, assign one third that kva to each of the three phases.

Please note that is an accounting technique, rather than a scientific description of actual events. It is the way that panel schedules are commonly filled in. If I had known that your were discussing panel schedules, I would have instantly understood your need.

[ April 02, 2003, 02:24 PM: Message edited by: charlie b ]