Quick Question - 3 phase load calc.

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Sharpie

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If I have all single phase loads on a 3 phase panel, which calc. do I use?

1. Watts (19951) / Volts (208) = 96A

or

2. Watts (19951) / Volts (208) x 1.73 = 166A

:confused:

Thanks,
 
Sharpie said:
If I have all single phase loads on a 3 phase panel, which calc. do I use?
1. Watts (19951) / Volts (208) = 96A
or
2. Watts (19951) / Volts (208) x 1.73 = 166A
Thanks,
Click to expand...

If 19951 watts is the total load, then amps = 19951/(208 x 1.73) = 74 amps for a balanced load
 
Bob,

I don't know why, but I just can't come up with 74A any way I do it.

I can come up with 55.44A

What steps are you taking?

Thanks,
 
Chris,
As Bob pointed out, the correct formula is: Amps = Power / (volts x the square root of 3)
If you round the square root of three to 1.73 you do come up with 5.44 A. per phase. If you plug the formula into a calculator you will come up with 55.378 A., but I doubt that you need that kind of acuracy! What are you figuring this for?
Wes
 
Sharpie said:
2. Watts (19951) / Volts (208) x 1.73 = 166A
Click to expand...
You either have to divide by the sqrt(3) or "group" volts times sqrt(3):
VA_3?total ? V_line-line ? √3 = A_avg.line, or

VA_3?total ? (V_line-line ? √3) = A_avg.line​
Alternatively, you can also calculate using line to neutral voltage of a wye system.
VA_3?total ? V_line-neutral ? 3 = A_avg.line, or

VA_3?total ? (V_line-neutral ? 3) = A_avg.line​
You should also not use the term Watts unless you know the power factor (pf).
W = V ? A ? √3 ? pf​
 
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