question for electrical experts

ok - I have a simple question. I will preface it by saying that it is against code most likely and should be written up but on the practical / real world side, exactly how dangerous in terms of possible overheating and fire is it if a 20 amp breaker has a 14 gauge copper wiring on it? It has 12 gauge on the circuit except for the last section where it is wired from an outlet inside to a gfci outlet outside with 14 gauge instead of 12. thank you for your help. (btw, i am a member so i am not sure why it says i am not above)

It does not really matter how dangerous it is for the possible overload situations that may occur.
If you do not report it correctly it is very dangerous to your inspection career.

When a house burns down all electrical problems found by the fire investigator are likely to be in his report regardless of whether or not they caused the fire. You don’t want to be on the news for not reporting an electrical issue on a house that had a fire.

I know that it should be reported, cause of concern, etc… but just for my own knowledge, i am curious about how dangerous this really is…

It IS a fire hazard and should be written up as such.

Let me pose a question - How dangerous is a faulty T&P valve. It is not, until the water heater goes bad and needs to release pressure. Then the valve will either work or you can have an explosion.

How many times have we heard of a fire in a home or apartment because the outlet had a faulty ground. Pecentage wise, a fire may not happen often, but I dont want to read about it in the paper or have a client call me. It is a life safety issue and needs to be addressed.

14 gauge NM wire is rated for 20 amps and limited to 15 amps for the purposes of the NEC. How dangerous? Depends on ambient temperature, air flow, distance to combustibles, length of cable, quality of the connections etc.

Hmm…says you are member on my screen…:slight_smile:

Basically you are right in that it is a code violation in the NORMAL sense…we can post exceptions to this but as many would say I tend to elaborate WAY too much in posts anyway…so I will be brief.

The problem here is obviously in that the 14 AWG will not be protected at its tested and listed allowance( excluding exceptions…if they apply…here they do not so dont assume just because it does to AC’s or other motors )…can it handle more…sure probably can for short periods of time…but what if the load is excessive for long periods…may be a problem.

We simply have to rely on the great people at the NFPA and many others who over the years contributed to the success of the NEC and it’s publications and increaseing the safety for people today.

Now…you are required to protect that circuit at 15 AMPS.

As for overheating…if the wire is overloaded it may heat up and quite possible cause a weakness in the insulation that may not happen IF the circuit was sized right…if that breaks down possible fires can happen.

Now I dont like to play Nostridomas…however you spell it…so i can’t comment on what will happen…can only comment on the concept of what COULD happen…

Also the heat buildup time respective to the OCPD trip time of a 20A breaker is more than a 15A breaker…so a 15A obviously trips sooner…in respect to its rating…so a 15A rated wire with long term exposure to overloading could heat up and cause issues well before the trip time and so on with regards to a point the 20A breaker may trip.

Here is a neat article on it…if you can understand the mathmatics involved…well beyond normal electrical calculations.

BTW- Here is the opening part to that article I linked above…VERY interesting and everyone should read it…

Jane is a recent graduate engineer working for an electrical consulting company (Eleck Inc.). She is given the job of laying out the wiring for a new home. In particular, she must specify the circuit breakers that protect the circuits to the wall plugs of each room and the ceiling lights. Normally these circuits are wired with AWG #14 wire and are protected by 115 V/ 15 A breakers.
A co-worker, Jerry, who is a mechanical engineer tells her that she should specify 115 V/ 20 A circuit breakers because each circuit then could handle higher current appliances or more appliances at a time. But the house will be wired with # 14 wire which has a continuous current rating of 15 A. Jerry’s reaction to this is “Oh, forget that the house will be wired with #14. The overload caused by the appliances will only last a few minutes and a 20 A breaker will provide adequate protection.” Subsequently, the house was built with the #14 wire installed in the appropriate circuits and protected with 115 V/ 20 A circuit breakers as specified by Jane.
Two months after the house was built and the family moved in, a fire occurred in the house causing $75,000 worth of damage. The fire marshall’s report stated that the fire was caused by an electric toaster having a short circuit in it. The report also stated that the short circuit current in the toaster was estimated to be 550 A and lasting for 10 seconds. The important parameters in causing an electrical fire is the energy from the electrical short and this energy is related to i2t. The i2t for this short circuit is approximately 3 x 106 amp2-seconds.
(i2t = 5502 x 10 seconds = 3 x 106 amp2-seconds)

Even if a #14 conductor was loaded for close to 20 amps repeatedly and didn’t start a fire, I believe the insulation would suffer over time from the conductor running very warm. Now this may not be an issue with newer Romex, but we have all seen what heat does to older Romex when we remove a ceiling light fixture that has been overlamped for years.

I would not immediately say #14 will burst into flames with 20a on it, or even get warm. There are too many listed appliances that use #14 inside for currents 20a or greater. There are usually in free air though. The real problem will probably show up as voltage drop and all of your 240.4(D) safety factor is gone so a miscalibrated breaker is more likely to be a problem. If course if it is FP a 15a probably isn’t going to trip either.


I gave possible issues…again not nostridomas…still not sure am spelling that right…but anything is possible which is the intent of the NEC and why it would be a violation…as something had to induce the code to make something a violation.

My example was a case study…showing just a possible condition.

I agree as stated…that chances are it wont burst into flames…lol…did anyone say that…not sure…but chances are it will never be loaded up anyway enough to be a problem…

BUT…the poster wanted a baseline for what could happen…and again is anything I stated not possible…?

It is a fine line we walk when we try to stay code complying and answer real world questions without drifting off into urban legends.
I heard someone the other day say 310.16 represented the temperature a wire would run at when loaded to the given ampacity.

lol…now thats a urban legend…

Thanks for posting this article Paul. I’ve always suspected that breakers have a built-in time delay.
From the article, “for a 15A breaker the i2t is 2,000,000 —”. So for a 15A breaker carrying a 15A load, if I did the math correctly, it wont trip for 148 minutes. For a 15A breaker carrying a 20A load it would be 83 minutes.
Now I understand how I can use my 1875W hairdryer on my 15A bedroom circuit without tripping the breaker.


I am so glad you found it helpful…now try not to KILL yourself…:slight_smile:

lol…I mean Kill youself by trying to see IF you can blow the circuit with that hair dryer…now that you are LOCKED into the MATH !..:slight_smile:

Your 1875w hair dryer probably only pulls about 13a

this is a question that at least several people ask me every year before x-mas.

too many lights on a 15 amp circuit…looking for a shortcut to a frequently tripping breaker.

when the smoke alarm wakes em’ up in the middle of the night, they’ll wish they hadn’t.

aside from being against code…it is a real risk that should not be taken.

Great. So I can use it as long as I want. Wish I had more hair.:slight_smile:

I have been doing this test on hair dryers for a couple years and this is actually the biggest number I have recorded. Most are more like 11.75-12a. I guess it ia all of that “ionic/ceramic technology”. I am not sure what the ionic part is all about but the ceramic part is a small slotted disk in the throat.

Well…how many lights per 15A circuit…well if you take it at FULL face value you have 1,800 watts available on the typical 15A circuit…

But honestly…I would not push it a dime over 1,500 Watts…:wink: