Tell me more ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.
up vote 8 down vote favorite

All of my heating is on one breaker, 240V on a double pole breaker, each marked 20A (it's a small condo). I wonder how I can determine the maximum wattage I can hook up to that breaker.

share|improve this question

1 Answer

up vote 13 down vote accepted

Power (Wattage) = Current x Voltage (P=I*V)

20A X 240V = 4800W

enter image description here

share|improve this answer
2  
Thus 40A * 240V = 9600W? It's been a while since I had science classes... and physics never was my strongest suit :( – MPelletier Jan 25 '11 at 2:31
8  
If a double pole breaker is marked as 20A then its 20A. Its not doubled because its a double pole. – Web Jan 25 '11 at 2:33
3  
That formula is for DC. For AC you also need to consider power factor, although for heating alone it's usually not a real concern. Just be aware that as a general rule it's not the correct formula for AC. – John Gardeniers Jan 25 '11 at 8:00
3  
+1, Although that will give an estimate only - the breaker will not have exactly 20A cutoff, just very close to that, so it might happen that it breaks the circuit on slightly lower or slightly higher current. – sharptooth Jan 25 '11 at 9:43
3  
not really 4800W. The reality it's that P=U*I and this gives you VA, in order to get W you need to multiply this with cosPhi, that you can take arround 0.8 to be safe (so it shoud be just a shade under 4000W) – s.mihai Jan 25 '11 at 11:26
show 6 more comments

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.