# wire sizing for wall heater?



## darren (Nov 25, 2005)

Watts/Volts=Amps
1500W/240V=6.25A

So you would be good with 14/2 on a 2pole 15A breaker.

So your fine with your 12/2 on a 15 or 20A breaker.


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## gerhops (Sep 21, 2008)

Thank you!


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## chris75 (Aug 25, 2007)

darren said:


> Watts/Volts=Amps
> 1500W/240V=6.25A
> 
> So you would be good with 14/2 on a 2pole 15A breaker.
> ...


You forgot to add 125% for electric heat.


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## theatretch85 (May 17, 2008)

By my calculation, 6.25 + 125% = 14.0625 amps. 80% of a 20 amp circuit would be 16 amps, so a 20 amp circuit would be adequate for the 2 heaters to be running at full. Good choice going with the 12 gauge wire instead of the 14! Definitely a very wise decision; its always better to have a little bit too large of a wire than not large enough!


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## chris75 (Aug 25, 2007)

theatretch85 said:


> By my calculation, 6.25 + 125% = 14.0625 amps. 80% of a 20 amp circuit would be 16 amps, so a 20 amp circuit would be adequate for the 2 heaters to be running at full. Good choice going with the 12 gauge wire instead of the 14! Definitely a very wise decision; its always better to have a little bit too large of a wire than not large enough!


 
Why are you adding 125% yet still using only 80% of a breaker? WAY OVERKILL!!!  A 15 amp breaker is perfectly fine.


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## jerryh3 (Dec 10, 2007)

theatretch85 said:


> By my calculation, 6.25 + 125% = 14.0625 amps. 80% of a 20 amp circuit would be 16 amps, so a 20 amp circuit would be adequate for the 2 heaters to be running at full. Good choice going with the 12 gauge wire instead of the 14! Definitely a very wise decision; its always better to have a little bit too large of a wire than not large enough!


Why are you adding 125%?


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## chris75 (Aug 25, 2007)

jerryh3 said:


> Why are you adding 125%?


 
You have to for electric heat, the problem is why is he only using 80% of the breaker.


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## theatretch85 (May 17, 2008)

Sorry, my bad; I don't do electric heat installations. Besides, last time I checked, a 15 amp breaker costs the same as a 20 amp breaker. He already has 12 gauge wire run, so connecting it to a 20 amp breaker wouldn't be an issue.


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## chris75 (Aug 25, 2007)

theatretch85 said:


> Sorry, my bad; I don't do electric heat installations. Besides, last time I checked, a 15 amp breaker costs the same as a 20 amp breaker. He already has 12 gauge wire run, so connecting it to a 20 amp breaker wouldn't be an issue.


 
The only rule is that you have to add 125%, but the reciprocal is 80%, but no need to do both.


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## jerryh3 (Dec 10, 2007)

chris75 said:


> You have to for electric heat, the problem is why is he only using 80% of the breaker.


210.19? If this is the only thing on the circuit, wouldn't it only need 125%(of the continuous load) protection?


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## theatretch85 (May 17, 2008)

chris75 said:


> The only rule is that you have to add 125%, but the reciprocal is 80%, but no need to do both.


Thanks, now I will know for the future in the event I ever have to deal with an electric heat install.


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## chris75 (Aug 25, 2007)

jerryh3 said:


> wouldn't it only need 125% protection?


 
Correct... my mistake if you misunderstood me.


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## chris75 (Aug 25, 2007)

theatretch85 said:


> Thanks, now I will know for the future in the event I ever have to deal with an electric heat install.


 
The Code reference is 424.3(B)


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## Pudge565 (Jan 27, 2008)

First off show ever said 14.xxx amps is wrong the math is 1500/240=6.25 amps them you need 125% so 6.25*1.25=7.8125 so a 15 amp breaker is way more than enough but you can put it on a 20 amp breaker if you so desire.


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## darren (Nov 25, 2005)

I did not mention it because the amperage was so low.

Anyways would it not be 6.25X125% not 6.25+125%. Which would give you 7.8A. I live in Canada and only know the Canadian Electric Code which treats the load differnetly then other loads but this could be rule of the NEC.


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## chris75 (Aug 25, 2007)

darren said:


> Anyways would it not be 6.25X125% not 6.25+125%.


 
Try it either way and see what you end up with.


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## jerryh3 (Dec 10, 2007)

chris75 said:


> Try it either way and see what you end up with.


You end up with two different numbers. 7.81 and 14.06


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## chris75 (Aug 25, 2007)

jerryh3 said:


> You end up with two different numbers. 7.81 and 14.06


 
I couldn't come up with 14.06, what am I doing wrong?


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## darren (Nov 25, 2005)

Chris they took 6.5x125% and then added that number to 6.5 to get you the 14A.

If you add or multiply you get the same answer, i just have never seen it written or said as adding 125%.

We both meant the same thing but written two different ways.


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## jerryh3 (Dec 10, 2007)

chris75 said:


> I couldn't come up with 14.06, what am I doing wrong?


125% of a number is the number plus 25%. When you say take the number and add 125% you're actually saying take x and add it to x*1.25. It should be take the number and add 25%.


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## chris75 (Aug 25, 2007)

jerryh3 said:


> 125% of a number is the number plus 25%. When you say take the number and add 125% you're actually saying take x and add it to x*1.25. It should be take the number and add 25%.


I know, I was not sure how you guys were coming up with 14 amps, most people, I thought would just multiply by 1.25, guess I thought wrong. :confused1:


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## kbsparky (Sep 11, 2008)

chris75 said:


> ... I thought would just multiply by 1.25, guess I thought wrong. :confused1:


Nope, you thought right.

You can EITHER take the full load and multiply by 1.25 OR you can take 125% of the full load. Both are the same thing. :whistling2:

You do NOT take the full load and add another 125% to that. Overkill, big time.

I get 7.8 Amps total needed for this circuit. Slightly over half of what a 15 Amp circuit can safely provide.


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