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09-21-2008, 01:24 PM   #1
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## wire sizing for wall heater?

I am installing two wall mounted convection heaters. One is 500 watts and the other is 1000 watts. I am trying to determine what gauge wire I should be using. I can not find any information on amperage. The instructions say to install it with 240 volt wire. The folks at the electrical supply said 14 but to play it safe 12 gauge. I have a book that says for 240 volts you should use 10 gauge wire and then in the same book it talks about installing a 240 volt baseboard heater and using 12/2 wire.
So I'm a bit confused! I have the 12/2 and am half way through installing the first one!
Thank you.
G

09-21-2008, 01:29 PM   #2
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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.

 09-21-2008, 01:41 PM #3 Newbie   Join Date: Sep 2008 Posts: 2 Rewards Points: 10 Thank you!
09-21-2008, 02:08 PM   #4
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Quote:
 Originally Posted by darren 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.
You forgot to add 125% for electric heat.

 09-21-2008, 03:14 PM #5 Member   Join Date: May 2008 Location: Apple Valley, MN, USA Posts: 1,002 Rewards Points: 506 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!
09-21-2008, 03:24 PM   #6
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Quote:
 Originally Posted by theatretch85 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.

Last edited by chris75; 09-21-2008 at 03:26 PM.

09-21-2008, 03:27 PM   #7
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Quote:
 Originally Posted by theatretch85 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!

09-21-2008, 03:28 PM   #8
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Quote:
 Originally Posted by jerryh3 Why are you adding 125%?

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

 09-21-2008, 03:31 PM #9 Member   Join Date: May 2008 Location: Apple Valley, MN, USA Posts: 1,002 Rewards Points: 506 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.
09-21-2008, 03:34 PM   #10
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Quote:
 Originally Posted by theatretch85 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.

09-21-2008, 03:36 PM   #11
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Quote:
 Originally Posted by chris75 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?

Last edited by jerryh3; 09-21-2008 at 03:39 PM.

09-21-2008, 03:37 PM   #12
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Quote:
 Originally Posted by chris75 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.

09-21-2008, 03:40 PM   #13
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Quote:
 Originally Posted by jerryh3 wouldn't it only need 125% protection?

Correct... my mistake if you misunderstood me.

09-21-2008, 03:42 PM   #14
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Quote:
 Originally Posted by theatretch85 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)

09-21-2008, 04:05 PM   #15
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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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