dwelling unit switch leg size

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mporterf

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Question....Can anyone tell me if the code allows for 20amp lighting circuit to feed a 15 and switch via #12 awg, then reduce the wire size down to #14 awg to feed the lighting load?
 
It's a practice I have seen accepted in some areas (mainly GA), but I know of no
Code section that allows it.
 
The 15A switch is fine as long as the lighting load is 15A or less. But in most cases you can't reduce the wire size as that is creating a branch circuit tap. Use of a branch circuit tap is quite limited.
 
I am amazed at how often this question is asked. It is definitely non compliant to undersize the switch leg as that switchleg is part of the branch circuit. Art 240.4(D) will not allow it unless you install a 15 amp breaker
 
Dennis Alwon said:
I am amazed at how often this question is asked. It is definitely non compliant to undersize the switch leg as that switchleg is part of the branch circuit. Art 240.4(D) will not allow it unless you install a 15 amp breaker
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We are doing a big addition and we are busy with several big projects so we subbed the electrical in the addition. They did what OP mentioned, bring power in on 12-2 and then 14-2 for switch legs (the county just adopted building codes for commercial and residential subdivisions, but this is neither so no inspection).

I didn't say a word about it because I'm sure I would get "we've always done it like this".
 
Dennis Alwon said:
I am amazed at how often this question is asked. It is definitely non compliant to undersize the switch leg as that switchleg is part of the branch circuit. Art 240.4(D) will not allow it unless you install a 15 amp breaker
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I once looked wayyy back to see if the practice was ever compliant and don't recall the result of my search , but it was allowed, by practice, in this area of GA and TN about 20 years ago and the practice died hard.
 
Its been done around here as well.
Any tap rule that is considered would mostly likely only apply to 18" and that being from the fixture.
In a search on this site this has been asked before and there is a wealth of info on how and why its not compliant.
Im only stating as I remember.
 
dwelling unit switch leg size

What's the article that allows us to use smaller gauge fixture whips?

Nvm found it. 410.117
 
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reduced conductor for switched legs was common here as well. There was no inspections in most single family dwellings in the area until about mid 1990's so nobody was correcting those that didn't know any better until that time.
 
The OCPD is the defining factor of the branch circuit rating & conductor size -- -- --- A good example of overside wires is for voltage drop
 
kwired said:
reduced conductor for switched legs was common here as well. There was no inspections in most single family dwellings in the area until about mid 1990's so nobody was correcting those that didn't know any better until that time.
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Another factor in earlier times was #14 60?C conductors were rated 20A. Not sure when Article 240 requirements for small conductors came into existence.
 
It's easy to understand why a couple of lights on #14 won't overload when on a 20a breaker, but I always thought the reason it is not allowed was due to short-circuit ratings. A 14-gauge wire experiencing a low-resistance short might not allow as much over-current as a 12-guage so it might slow the magnetic tripping of a 20a breaker.

Of course likely the other reason is how murky things would get out in the field if electricians were left to determine when #14 was allowable on a 20a circuit. Can you imagine trying to write a clear code section about that?
 
edlee said:
Of course likely the other reason is how murky things would get out in the field if electricians were left to determine when #14 was allowable on a 20a circuit. Can you imagine trying to write a clear code section about that?
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It is allowed in some conditions - like motor circuits. Take 10HP 460 volt three phase motor and you can have 75 Deg 14 AWG conductors and up to a 35 amp breaker and be code compliant. But motor circuits also have motor overload protection that inherently protects the conductor as well from overload.
 
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