wattage of 3-phase heater bank

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rickymcc

rickymcc

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Murfreesboro , Tn
Can someone tell me the formula for figuring the wattage of a three phase heater bank. I know the voltage and the resistance between each phase hook-up. The heaters are not marked and i wish to calculate this to order the correct wattage bank.
I know ohm's law, but i don't think i can use it on a three-phase problem without some substitution. This knowledge would also be helpful if you needed to size conductors to the bank. If more information is needed let me know.
The resistance between conductors of the heater bank is 24 ohms. The voltage is 240v phase to phase.
 
Re: wattage of 3-phase heater bank

rick,
Assuming the measured resistance between any two load terminals is 24 ohms, it works out to approximately 4800 watts (4.8 kw) total, but the actual calculations would depend on the way the three individual heater elements are connected internally, wye or delta.

Ed

3%20Ph%20Heater1.gif


[ July 11, 2004, 12:13 PM: Message edited by: Ed MacLaren ]
 
Re: wattage of 3-phase heater bank

Something to think about.

A quote from a page of Uglys guide.

The electrical power in any part of a circuit is equal to the current in that part
multiplied by the voltage across that part of the circuit.


Ronald :)
 
Re: wattage of 3-phase heater bank

thanks ed and ronald.
your diagrams were a big help. I have one other question, the figured phase voltage for the wye connected bank was 138.7 volts. I know this circuit forms a voltage divider, I thought the voltage would have been 120 volts. Where did the 138 volts come from? Other than that it is exactly what i needed to know. The heater bank was bad so i couldn't get an amperage draw to use ohm's law on the wattage calculation.
thanks,
Ricky
 
Re: wattage of 3-phase heater bank

Ricky the 138v would be 240 / 1.732 = 138v

120v per phase would be if the phase to phase voltage were 208

Roger

[ July 12, 2004, 12:12 PM: Message edited by: roger ]
 
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