Power Across Phases for Double Pole Breakers

[z19ajm]

I have an equipment spec that's listed as the following:

Voltage = 220
Single Phase
Frequency = 60Hz
Current = 20A
Power = 4000W

That said, if I assume the p.f. to be 1.0, the VA should be the same as the power, which is 4kVA, correct?

If I'm using a 120/208Y, 3 phase, 4 wire panel, the 220V spec indicates I should be using a double-pole breaker, correct?

Also, let's say it is a double-pole breaker for this equipment and I put it across A & B phase, does each phase read 2kVA (assuming my first question is correct, I divided 4000VA by 2), or does each phase read 4kVA? What about if it was a 3-pole breaker?

Thanks!

 

[charlie b]

To start with, 20 amps times 220 volts is 4400 VA. If the equipment is specified at 4000 watts, then the power factor is 4000/4400, or about 91%.

Secondly, if the equipment calls for 220 volts, you cannot supply it from a 208 volt source. The equipment might be rated by its manufacturer to run at a range of voltages that extends from 208 through 220. But you would need to verify that, before you connect it to the 120/208 volt panel.

Now let me change your description, so that I can answer the question that I think you are asking. Suppose I had a 4 KVA load that calls for single phase, 208 volts. I could connected it between phases A and B. When I showed this component on a panel schedule, I would show 2KVA on phase A and 2 KVA on phase B.

Welcome to the forum.

 

[GoldDigger]

The actual VA on each of the two lines would be more than 2kVA but less than 4kVA because of the phasor math involved. But for practical purposes we can allocate it as if it were 2kW on each lead and more than 2kVA when calculating current on that phase line from that load alone. .
If you balance single phase loads across all three phases, then the net kVA and the net kW will match and will be related by the load power factor.
So that is what you would use on the panel schedule.

 

[z19ajm]

Awesome, thank you! So much easier to ask then figure it out myself.

So I can assume the same applies if it's a three phase load, correct? If the equipment spec calls for a 3KV load at 208 3-phase, I can assume that on the panel schedule it should read 1kV for each phase A, B, C?

 

[charlie b]

If you don't mind my substituting KVA for KV in this last question, the answer is yes.

 

[jumper]

If you don't mind my substituting KVA for KV in this last question, the answer is yes.

Can I nit pick and say I prefer kVA?

 

[kwired]

And if the load is equally balanced across all three lines.

 

[charlie b]

Can I nit pick and say I prefer kVA?

Do you say nEEther or nIIther? Oh, let's just call the whole thing off. :lol:

 

[Smart $]

Awesome, thank you! So much easier to ask then figure it out myself.

So I can assume the same applies if it's a three phase load, correct? If the equipment spec calls for a 3KV load at 208 3-phase, I can assume that on the panel schedule it should read 1kVA for each phase A, B, C?

That is correct. On a panel schedule you use the circuit load VA (or kVA) divided by the number of connected lines and enter that value in the respective columns.

 

[ggunn]

Awesome, thank you! So much easier to ask then figure it out myself.

So I can assume the same applies if it's a three phase load, correct? If the equipment spec calls for a 3KV load at 208 3-phase, I can assume that on the panel schedule it should read 1kV for each phase A, B, C?

Very loosely stated, power divides between/among phases and current does not.

 

[z19ajm]

Thank you everyone!