Calculating 240V power/wattage


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Old 11-03-17, 05:12 PM
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Calculating 240V power/wattage

I live in a house with radiant ceiling heat via resistive heating elements. I'd like to determine how much current the heater draws. I attached a clamp on ammeter to each of the hot/black leads coming out of the 2 breakers which serve the heater, one lead at time. One lead read 0, the other read 24 amps. I understand that P=IxV, but I'm a little confused on the total draw for a 240 line, with the 2 "hot" leads. Would it simply be 24x240=5760 watts? Why would the one lead read 0? Is that normal? I believe the clamp was completely closed, but possibly not.
 
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Old 11-03-17, 06:20 PM
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If the heat is 240V you should get the same amp reading on each leg.
 
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Old 11-03-17, 06:54 PM
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Would it simply be 24x240=5760 watts?
Yes.

But you know the current. It's 24A.
The wattage is 5760.

But like mentioned.... you should be reading the same 24A on both lines off the breaker. Is that a 2P30A breaker ?
 
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Old 11-03-17, 08:08 PM
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Thanks for the replies. I'm guessing I didn't have the clamp completely closed on the zero read, that lead was a bit harder to get the clamp onto, in the box. I'll have to pull the panel cover again to double check. Yes, it's a double 30 amp breaker.
 
 

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