20 Amp Circuits

J

Jimmy7

Senior Member
Location
Boston, MA
Occupation
Electrician
A couple of us were discussing a circuit we found last week in an older home. At the end of a 20 amp parallel circuit we found that someone installed 14 gauge cable for a switch and one light. Some of us are under the opinion it’s technically okay since the amperage is not going go any higher than what the light is drawing at the end of the circuit, why others are stating it’s just wrong.
 
You're both right. It is current-limited by the nature of the load. No one will plug a space heater into the light on the ceiling. But there is no allowance in the code for such an install either. It is a code violation.

And what do you mean "parallel circuit"?
 
CoolWill said:
You're both right. It is current-limited by the nature of the load. No one will plug a space heater into the light on the ceiling. But there is no allowance in the code for such an install either. It is a code violation.

And what do you mean "parallel
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It was just a regular 120v 20 amp circuit in a basement. I just mentioned parallel so you would know that the #14 would just be handling the section that light was on.
 
Penny pinching installers. What other code sections did they cut corners on?

The NEC is definitely overly conservative when it comes to protecting small conductors, but it says what it says and, to my knowledge, this had never been allowed.
 
The breaker's job is to protect the wire from becoming overheated due to excessive current, a situation that could result in a fire. The nature of the load (i.e., the light) is not the issue. Any weakness or failure of the wire's insulation (e.g., rubbing against the body of the light fixture) could result in leakage current.
 
Jimmy7 said:
A couple of us were discussing a circuit we found last week in an older home. At the end of a 20 amp parallel circuit we found that someone installed 14 gauge cable for a switch and one light. Some of us are under the opinion it’s technically okay since the amperage is not going go any higher than what the light is drawing at the end of the circuit, why others are stating it’s just wrong.
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A short circuit or a ground fault would pull more amps than just the light.
 
Jimmy7 said:
It was just a regular 120v 20 amp circuit in a basement. I just mentioned parallel so you would know that the #14 would just be handling the section that light was on.
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That is not a parallel circuit. A parallel circuit is 2 conductors connected together at both ends of the run. So you could have 2- 1/0 conductors run together and connected together in the panel and at the load end.
 
charlie b said:
The breaker's job is to protect the wire from becoming overheated due to excessive current, a situation that could result in a fire. The nature of the load (i.e., the light) is not the issue. Any weakness or failure of the wire's insulation (e.g., rubbing against the body of the light fixture) could result in leakage current.
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Couldn't that result in leakage current with properly sized wire too?
 
Jimmy7 said:
It was just a regular 120v 20 amp circuit in a basement. I just mentioned parallel so you would know that the #14 would just be handling the section that light was on.
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So yes that is a parallel circuit although not really relevant to your question. Parallel conductors would be two or more conductors connected at both ends which is not what you meant.
 
xformer said:
A short circuit or a ground fault would pull more amps than just the light.
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This. Just to have a pedagogical moment and expand a bit. The three main problems you can have that result in over current are overloads, short circuits and ground faults. The general rule is that an ocpd is at the start of the circuit and will protect against all three. An OCPD at the end will protect against overloads only. We are only allowed to do that only in limited applications like tap conductors. Taps are quite restricted, especially for branch circuits.
 
xformer said:
A short circuit or a ground fault would pull more amps than just the light.
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And a 20 amp breaker will protect 14 AWG from short circuits and ground faults. The trip time of 15 and 20 amp breakers when there is a short circuit or ground fault is almost identical.
 
It is definitely a violation, even if the possibility of a problem in the future is low.

I also ran into this recently. A few lights and a receptacle were added in a #14 run off a #12 dining room circuit. If it was only lights, I probably would have just stuffed a note in the box for anyone in the future and called it a day. But, the receptacle put me over and I ripped it all out and redid it in #12. Yes, a PITA.

If this #14 run is easy to replace, I'd do that. If not and it has little possibility of someone tapping it for a receptable, I might just put a note in the box and leave it there.
 
As long as it’s not one of the required 20 amp circuits, just install a 15 amp breaker done.
For the next installer, just put a little tab inside it says fuse down because of 14 on 12 something so the next moron doesn’t mess it up
 
electrofelon said:
Well yeah, ok, but we are not permitted to decide when we can reduce conductor size. I don't think that is the best response to address the OP's question.
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You're right, but for the sake of edification, I think it's good to be truthful. The breathless dramatic warnings about fire and destruction are disingenuous. The truth is, a #14 on a 20 amp breaker is a code violation. It is also not really going to spontaneously ignite and kill the family.
 
electrofelon said:
Well yeah, ok, but we are not permitted to decide when we can reduce conductor size. I don't think that is the best response to address the OP's question.
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It is a technical response to a comment that suggested that the 20 amp OCPD could not protect the 14AWG from short circuits and ground faults...nothing more should be read into my statement.
 
CoolWill said:
You're right, but for the sake of edification, I think it's good to be truthful. The breathless dramatic warnings about fire and destruction are disingenuous. The truth is, a #14 on a 20 amp breaker is a code violation. It is also not really going to spontaneously ignite and kill the family.
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Where the switch supplies a single lighting outlet, I think you can make a case for using fixture wire as a tap to the lighting outlet, with the tap originating at the load side of the switch. If we do that we can run up to 50' of 18AWG fixture wire to the luminaire on a 20 amp branch circuit. See 240.5(B). The feed to the switch would still have to be 12 AWG.
In this application the 14 AWG is not fixture wire so it is a violation, as the rule in 240.5(B) only applies to fixture wire. 402.10 permits us to use fixture wire to connect a luminaire to a branch circuit, and while this would not be the typical use of that rule, I believe it applies where there is only a single lighting outlet.
 
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