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Old 06-24-2009, 02:44 PM   #16
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14 gauge wire 20 amp circuit


Thanks everyone
did it all with the yellow 12 GA,

The jacket is as thin as the old 14 GA anyway.

Yes I used 15AMP receptacle for this add on.


I have gotten 20 AMP receptacle on my microwave and dishwasher circuits.
microwave being the only thing on the circuit, calls for a 20 AMP receptacle even the plug is 15AMP style
plus, it have great plug retention

Last edited by DIYGST; 06-24-2009 at 02:46 PM.
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Old 06-24-2009, 04:39 PM   #17
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14 gauge wire 20 amp circuit


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Yes, they are.

And just to be clear, while it is a violation to use 14ga wire on a 20A circuit in most cases, the 14ga wire will not burst into flames or all the insulation melt off if the current goes to 20A.
No, but the temp. rise above ambient will be (20/15)^2 times what it would be if the wire carried 15A.
I guess the insulation will just get brittle faster.
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Old 06-24-2009, 07:32 PM   #18
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14 gauge wire 20 amp circuit


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No, but the temp. rise above ambient will be (20/15)^2 times what it would be if the wire carried 15A.
I guess the insulation will just get brittle faster.
Not really. Remember, the listed ampacity for 14ga THHN (which is really what NM-B is) is 25A. It's the NEC that mandates, for most applications, the OCPD be limited to 15A.
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Old 06-24-2009, 08:47 PM   #19
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14 gauge wire 20 amp circuit


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Not really. Remember, the listed ampacity for 14ga THHN (which is really what NM-B is) is 25A. It's the NEC that mandates, for most applications, the OCPD be limited to 15A.
OK, so the temp rise at 25A is ~(25/15)^2 = 2.8x what the rise would be at 15A. I hope it's less than 90C, for a 30C ambient.
http://www.tcforensic.com.au/docs/article10.html

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Old 03-05-2013, 12:00 PM   #20
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14 gauge wire 20 amp circuit


I have a office with multiple appliances it 12 gauge wire throughout with a 15 amp breaker I want to change the breaker to 20 amp do you see any problem with this?
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Old 03-05-2013, 12:06 PM   #21
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14 gauge wire 20 amp circuit


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Yep, 20A breaker needs 12 gauge wire as per code.

But here is a theoretical question that makes sense in my mind. Let's say you have a few outlets on a 20A breaker and all are wired with 12 gauge wire. Assume you want to add a doorbell, and you tap power off of the last outlet in that 20A circuit. So you have to run wire from that last outlet to the 12 or 16 volt doorbell transformer. So beyond the outlet, the only possible draw of power will be the dinky little doorbell. So why wouldn't a gauge smaller than 12 be allowed between that last outlet and the doorbell transformer since it doesn't seem possible that anything beyond that last outlet will be drawing a lot of amps? I would think it would be okay to just use 14 guage between the outlet and the doorbell transformer. But I assume the answer is no. Just curious if anyone has any insight. Thanks.
If you tap off that 12 and use 14 then someone uses that feed to instead supply a heater and not a doorbell or ties into it to supply something else. Then you could have someone drawing more power than the wire is rated for. Just easier to keep the same gauge wire on the whole circuit.
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Old 03-05-2013, 12:40 PM   #22
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14 gauge wire 20 amp circuit


Is there anything wrong with #14 to #12 tails on a a 20amp circuit?
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Old 03-05-2013, 12:48 PM   #23
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14 gauge wire 20 amp circuit


This really should be a new thread. This one is from 2009.
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Old 03-05-2013, 12:51 PM   #24
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14 gauge wire 20 amp circuit


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I have a office with multiple appliances it 12 gauge wire throughout with a 15 amp breaker I want to change the breaker to 20 amp do you see any problem with this?
As long as you are sure it is all 12 gauge and copper wire.

I agree with Al, this thread is from 2009.
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Old 03-05-2013, 04:15 PM   #25
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14 gauge wire 20 amp circuit


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Is there anything wrong with #14 to #12 tails on a a 20amp circuit?
Yes, it's a code violation.
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