Calculation

[LANDON1]

What is the formula to find out what the amperage of a 30kw heater, 3 phase at 120/208 volts would be

 

[augie47]

I= P/E x 1.732

If applicable, don't forget 422.10 & 424.3 when selecting a conductor

 

[skeshesh]

Augie is correct - I'd just add that technically you do also need to account for the power factor (i.e. go from KW to KVA): I = ( P(KW)/P.F. ) / E * sq. root(3). Assuming a PF of 0.8 or so should be a safe bet since I'm guessing that you don't know the power factor. But the best way, and one I use everytime possible, is give the mfg. a call and ask the nameplate rating!

 

[don_resqcapt19]

The power factor of an electric heater should be very close to unity. The major portion of the load is resistive.

 

[skeshesh]

The power factor of an electric heater should be very close to unity. The major portion of the load is resistive.

Don is correct. It had been a long day and I overlooked this - my mistake.

 

[bnwitt@yahoo.com]

Three phase current formula

Three phase current formula

Wouldn't that be:

I=(P/E)/1.732

 

[mbeatty]

Wouldn't that be:

I=(P/E)/1.732

You are correct.
Mark

 

[Dennis Alwon]

I think that is the same as what Gus was saying. Look at the denominator as E x 1.73

 

[mbeatty]

I think that is the same as what Gus was saying. Look at the denominator as E x 1.73

That is another way to look at it. Thanks for the clarification.
Mark