#8 Romex max size breaker

[Patrick Kennedy]

Hi folks,

The question: Should a #8 gauge romex (type NM) wire be protected by a 40Amp DP breaker, or a 50Amp DP breaker.

Here's the situation: A #8 guage Type NM (Romex) wire was ran to the range/oven in the kitchen. This house is only 3-4 years old. There was a 50Amp DP breaker protecting it. While at the home doing some additional work for the customer we changed it to a 40Amp DP breaker as per code requirements.

The electrical contractor that originally wired the house was called by the customer to pay for this mistake in his wiring. Now I am having a challange with our local AHJ on the proper interpretation of the code. It is my understanding the maximum size breaker for all type NM cable (Romex) installations has to be taken out of the 60 degree column of Table 310.16.

I know there are different codes that ultimately point you back to using the 60 degree column. One being; 334.80

The local inspector is saying that they allow a 50Amp breaker on this #8 Type NM (Romex) as per their right under the AHJ rules. They say that there is THHN wire inside the overall jacket of the NM cable. That is why they can allow a 50A breaker. I do not believe that they can do that.

It also is my understanding that there are limitations on what the AHJ can do as per the following:
According to Article 90.4 covers enforcement and Authority Having Jurisdiction may grant special permission. However, these special permissions may not supersede the safety standards of the NEC according to Article 90.2(c) which covers special permission, as well as, Article 90.4. Article 90.4 states "by special permission the authority having jurisdiction may waive specific requirements in the Code or permit alternate methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety".

If someone out there can give me a definite answer on this I would really appreciate it. And if you can state the code articles on it too, that would be very benefical

Thank a lot

Patrick Kennedy

 

[infinity]

The NEC requires NM cable to be used at it's 60 degree C ampacity even if the conductors within the cable are rated for 90 degrees, see 334.80. Look up the conductor ampacity in 310.16 based on 60 degrees C and the conductor size. It's as simple as that.

Welcome to the forum.

 

[pete m.]

If someone out there can give me a definite answer on this I would really appreciate it. And if you can state the code articles on it too, that would be very benefical

Thank a lot

Patrick Kennedy

I believe that you know the answer and have provided all the code sections. Unfortunately it would seem that you are between the proverbial "rock and hard place"

Pete

 

[ivsenroute]

The NEC requires NM cable to be used at it's 60 degree C ampacity even if the conductors within the cable are rated for 90 degrees, see 334.80. Look up the conductor ampacity in 310.16 based on 60 degrees C and the conductor size. It's as simple as that.

Welcome to the forum.

There you have it. That is the answer.

The AHJ has no legal authority to overrule the NEC and would be stepping beyond his legal authority if allowing a 50A breaker.

What other rules could he be making up at the safety of others?

 

[acrwc10]

In your situation, you are correct. If there were an A/C unit or motor involved, then a larger OCP "may" be allowed. As far as the inspector saying there is THHN in side the NM cable ask him to show proof of that ( more than it looks like THHN so it must be THHN ) and ask him if the THHN was to be in a high ambient temp would he disregard the temp derating ? Or if there were more then 3 CCC's bundled would that not also need to be derated ?

 

[iMuse97]

It also is my understanding that there are limitations on what the AHJ can do as per the following:
According to Article 90.4 covers enforcement and Authority Having Jurisdiction may grant special permission. However, these special permissions may not supersede the safety standards of the NEC according to Article 90.2(c) which covers special permission, as well as, Article 90.4. Article 90.4 states "by special permission the authority having jurisdiction may waive specific requirements in the Code or permit alternate methods where it is assured that equivalent objectives can be achieved by establishing and maintaining effective safety".

I think you are correct, and have correctly interpreted the NEC. Convincing the AHJ may be another matter altogether, and probably not a win-win situation, in this case. The AHJ is going to maintain the position that they know that they are establishing and maintaining effective safety of the installation. It's a matter of authority of interpretation at that point, and they have it. However, ACR (post above) has a good point that may assist you if you can keep the discussion very focused, business-like (ie. unemotional), and rational.

Anyway, welcome to the forum.

 

[don_resqcapt19]

I am sorry, but the AHJ can make any change they want to the NEC. There are no restrictions on this.

 

[electricmanscott]

This is a good example of why having your location visible should be mandatory.

 

[mivey]

I am sorry, but the AHJ can make any change they want to the NEC. There are no restrictions on this.

Troublemaker. :grin:

 

[mivey]

This is a good example of why having your location visible should be mandatory.

Easy enough to ask if someone feels like sharing. Not everyone is so open with their information.

Just base your answers on the information given. We hardly ever get the full story anyway.

 

[iMuse97]

I am sorry, but the AHJ can make any change they want to the NEC. There are no restrictions on this.

Having worked in Illinois for 10 years, I can vouch for that!:grin:

Having worked in Indiana for just as long, I know that in Indiana you can call to Indianapolis and get the local inspector overruled if you "never plan to work in his jurisdiction again." :roll:

But seriously, I agree with you, Don; my previous post did not imply that. However, I try to have good working relationships with an inspector, and see things their way, or just do it their way, even if I don't see it their way.

 

[peter d]

C'mon, everybody knows that Patrick Kennedy is a Congressman from Rhode Island.

I am sorry, but the AHJ can make any change they want to the NEC. There are no restrictions on this.

Now I am truly baffled. Are you saying the AHJ can make up rules on the spot without them being written into a law or adopted code? Coming from you this sounds strange because you have always taken that position that the rules being enforced must be codified.

Regarding the ampacity of the cable in this situation- the NEC is very cut and dry about it. I don't see how the AHJ can allow a situation that will possibly exceed the NEC rated ampacity of the cable.

 

[electricmanscott]

Easy enough to ask if someone feels like sharing. Not everyone is so open with their information.

Just base your answers on the information given. We hardly ever get the full story anyway.

Will do.

AHJ can do whatever they like with the NEC including adopting as is, not adopting at all, or changing it as they see fit, however foolish, misguided or ridiculous those changes may be.

Now if I knew the OP was here in MA my answer would be different even though what I said would remain true.

 

[growler]

The local inspector is saying that they allow a 50Amp breaker on this #8 Type NM (Romex) as per their right under the AHJ rules. They say that there is THHN wire inside the overall jacket of the NM cable. That is why they can allow a 50A breaker. I do not believe that they can do that.

Yes the local inspector may be letting contractors get away with installing 50 Amp breakers on #8 but are they willing to put it in writing and sign it.

I have always thought of special permission as a formal process and not just the inspector saying go ahead. When you get right down to it the contractor is responsible for a safe installation no matter how dumb the inspector is.

 

[mivey]

Will do.

LOL. I did not mean to sound tart. It was a suggestion. You have my permission to respond as you please. :grin:

 

[winnie]

Now I am truly baffled. Are you saying the AHJ can make up rules on the spot without them being written into a law or adopted code?

I believe he is saying that the jurisdiction which adopts the code (giving it force of law) can make any changes that it wants. These changes must be written into law (not just the whim of the examiner), but might include significant examiner discretionary power.

-Jon

 

[peter d]

I believe he is saying that the jurisdiction which adopts the code (giving it force of law) can make any changes that it wants. These changes must be written into law (not just the whim of the examiner), but might include significant examiner discretionary power.

-Jon

Yes, I see that now. Still, I don't see how an AHJ can relax a clear cut NEC rule which would essentially create a violation of the NEC.

 

[jaylectricity]

Yes, I see that now. Still, I don't see how an AHJ can relax a clear cut NEC rule which would essentially create a violation of the NEC.

I'll bet the circuit breakers are allowed to be a much higher ampacity in an igloo.

 

[don_resqcapt19]

C'mon, everybody knows that Patrick Kennedy is a Congressman from Rhode Island.





Now I am truly baffled. Are you saying the AHJ can make up rules on the spot without them being written into a law or adopted code? Coming from you this sounds strange because you have always taken that position that the rules being enforced must be codified.

Regarding the ampacity of the cable in this situation- the NEC is very cut and dry about it. I don't see how the AHJ can allow a situation that will possibly exceed the NEC rated ampacity of the cable.

The inspector is not the AHJ...the adopting authority is.

 

[mivey]

The inspector is not the AHJ...the adopting authority is.

But as the mouthpiece of the authority, they become the resident arm of the AHJ. When you need a local interpretation, they become the AHJ, unless you go over their head.

Kind of like the police making a subjective call on whether you were acting "threateningly" or driving "too fast for conditions", etc. The officer essentially becomes the local interpretation of the law.