# 14 gauge wire 20 amp circuit



## Plumbvoltage (Dec 2, 2008)

If it has a 20amp breaker it must have 12 gauge wire.:yes:


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## Scuba_Dave (Jan 16, 2009)

No you can't use 14g on any part of the 2 appliance circuits & they must be 12g 20a by code
The outlets are rated 15a (like each plug) & 20a pass thru


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## DIYGST (Nov 13, 2008)

I see !! thanks for that.


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## adpanko (Jun 18, 2009)

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.


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## DIYGST (Nov 13, 2008)

adpanko said:


> 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.


You can do all kinds of things that makes sense but I would think, code is code.
That's not to exclude the possibility that in 20 years you are changing out that door bell for a laser sentry gun that draws 16 amps.


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## Scuba_Dave (Jan 16, 2009)

DIYGST said:


> You can do all kinds of things that makes sense but I would think, code is code.
> That's not to exclude the possibility that in 20 years you are changing out that door bell for a laser sentry gun that draws 16 amps.


And what would prevent someone from seeing that 14g in the future & connecting a heavier load? Then someone else realizes the 20a breaker shuts off power to that device & puts in an even heavier load
Code is there for a reason...12g wire....20a breaker
14g wire =15a breaker

You can't always prevent someone from doing something wrong
But code tries to prevent problems
My last house was 100 years old - many owners
This house is going on 60 years old - quite few owners too
Some houses change ownership every 5 years or less


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## Gary_602z (Nov 15, 2008)

Or what if you picked up a dead short at the transformer or someplace in the #14 wire? Nice fried wires.

Gary


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## Daniel Holzman (Mar 10, 2009)

The entire theory of wire gauge size and breakers is based on protecting the WIRE from overcurrent conditions. The devices have their own protection. So the theory is that a circuit protected with a 20A breaker could have up to 20 amps on the wire before the breaker blows. Therefore, a fault on any downstream device (i.e. the doorbell) could cause up to 20A of current on the 14 gauge wire.

In theory, the insulation on the 14 gauge wire could overheat given the overcurrent (20A) condition, potentially causing a fire. While this is unlikely, it is the reason why code prohibits less than 12 gauge wire on a 20A circuit.


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## ScottR (Oct 6, 2008)

Gary_602z said:


> Or what if you picked up a dead short at the transformer or someplace in the #14 wire? Nice fried wires.


To be fair, a dead short would overheat _any_ wire if power were not cut by the OCPD.

The breaker would trip before the #14 would fry (hopefully).



Daniel Holzman said:


> The devices have their own protection.


Which devices? Most do not.. The OCPD should be sized for the lowest rated component of the circuit. If you used all #12 wire, but connected a receptacle inline with the branch wiring that was rated for max. 15A pass-through, the circuit would have to be protected by a 15A OCPD.


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## DIYGST (Nov 13, 2008)

But most recepticles I buy now is 20A passthrough, right?


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## adpanko (Jun 18, 2009)

DIYGST said:


> But most recepticles I buy now is 20A passthrough, right?


Any 20A outlet you buy now should look like this:










Notice has the neutral slot has the additional little slot coming off of it at 90 degrees. A 15A outlet won't have that perpendicular slot coming off the neutral slot. But the fail proof method to see the amperage of the outlet is to read the back and/or side; it will always say.


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## HouseHelper (Mar 20, 2007)

DIYGST said:


> But most recepticles I buy now is 20A passthrough, right?


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.


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## ScottR (Oct 6, 2008)

DIYGST said:


> But most recepticles I buy now is 20A passthrough, right?


Yes, but not all.. *If* it were rated for 15A pass-through, it should not be on a 20A breaker.


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## Scuba_Dave (Jan 16, 2009)

adpanko said:


> Any 20A outlet you buy now should look like this:
> 
> 
> 
> ...


There is no need to buy a 20a outlet unless you have a 20a plug
The 15a outlets are rated as 20a pass-thru
A good place for a 20a outlet woudl be in the garage/shop
I've yet to own any tool that has a 20a plug on the end


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## DIYGST (Nov 13, 2008)

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


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## Yoyizit (Jul 11, 2008)

HouseHelper said:


> 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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## HouseHelper (Mar 20, 2007)

Yoyizit said:


> 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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## Yoyizit (Jul 11, 2008)

HouseHelper said:


> 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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## scaponio (Mar 5, 2013)

*15 amp change to 20*

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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## rrolleston (Oct 17, 2011)

adpanko said:


> 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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## sirsparksalot (Oct 16, 2010)

Is there anything wrong with #14 to #12 tails on a a 20amp circuit?


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## al_smelter (Feb 15, 2013)

This really should be a new thread. This one is from 2009.


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## jbfan (Jul 1, 2004)

scaponio said:


> 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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## stickboy1375 (Apr 28, 2012)

sirsparksalot said:


> Is there anything wrong with #14 to #12 tails on a a 20amp circuit?


Yes, it's a code violation.


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