Switch leg wire size

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construct

construct

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I am an Inspector and I had a contractor ask me about using 14 ga wire for his light fixture switch legs on a 20amp branch circuit. My initial thought is that the switch leg wire must have the ampacity of the branch circuit rating. The only thing I find in the NEC is where it talks about fixture wires being a minimum of 18ga and that they cannot be used as branch circuit conductors. I must be missing something. Help please.
 
construct said:
I am an Inspector and I had a contractor ask me about using 14 ga wire for his light fixture switch legs on a 20amp branch circuit. My initial thought is that the switch leg wire must have the ampacity of the branch circuit rating. The only thing I find in the NEC is where it talks about fixture wires being a minimum of 18ga and that they cannot be used as branch circuit conductors. I must be missing something. Help please.
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Fixture wires (Art 402) is not where you would look for this requirement.
Art 210 Branch Circuits is where the requirements can be found.
Art 240 Overcurrent Protection also.

You will find that the requirement of the size of the conductor for switch leg is to be sized according to the overcurrent device supplying the circuit in question.
 
Cavie said:
How did the undersized sw leg noncence ever get started??????
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An undersized switch leg is _not_ nonsense at all. Under the NEC it is an unacceptable design, because the switch leg conductors would not be considered protected by the OCPD. But other parts of the NEC permit various components with ratings smaller than the OCPD rating, as long as they are sufficient for the load served.

For example, you can have a 20A 120V circuit, with a 10A switch feeding a 1000W load. You would be required to use a minimum of 12ga Cu conductors, but that 10A switch is perfectly acceptable.

The short 'fixture wires' which are part of the fixture itself are much smaller than the circuit wiring. These conductors are not protected from overload by the OCPD, but are considered acceptable by UL because they are sufficient for the load served.

Thus it is not intuitively obvious that circuit conductors could not be similarly reduced in size to match the particular load served. It is simply an NEC rule that you must match the circuit conductors to the OCPD in this case.

-Jon
 
winnie said:
The short 'fixture wires' which are part of the fixture itself are much smaller than the circuit wiring. These conductors are not protected from overload by the OCPD, but are considered acceptable by UL because they are sufficient for the load served.


-Jon
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I would add that a field installed fixture whip with 6' of 3/8" FMC and #18 conductors is permitted on a 20 amp circuit. The smaller gage conductors need not be part of the fixture itself.
 
240.5 (B) (2).
Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(3) 20 ampere circuits - 14 AWG and larger.
 
Rich Elec. said:
240.5 (B) (2).
Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(3) 20 ampere circuits - 14 AWG and larger.
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You missed #1:


240.5(B)(2) Fixture Wire. Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(1) 20-ampere circuits ? 18 AWG, up to 15 m (50 ft) of run length
(2) 20-ampere circuits ? 16 AWG, up to 30 m (100 ft) of run length
(3) 20-ampere circuits ? 14 AWG and larger
(4) 30-ampere circuits ? 14 AWG and larger
(5) 40-ampere circuits ? 12 AWG and larger
(6) 50-ampere circuits ? 12 AWG and larger
Click to expand...
 
Yes, you can use fixture wire, but only between the outlet on the branch circuit to the supplied equipment. This permits the use of the small conductor fixture wire on 20 amp circuits for fixture whips, but would not permit it between the switch and the fixture.
Article 100 definition "branch circuit"
402.11
Don
 
Rich Elec. said:
240.5 (B) (2).
Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(3) 20 ampere circuits - 14 AWG and larger.
Click to expand...
Switch legs are NOT fixture wires
Switch legs are part of the BRANCH CIRCUIT.



In Infinity's example ( 240.5(B)(2) ):
Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following...

Two different animals.
 
infinity said:
I would add that a field installed fixture whip with 6' of 3/8" FMC and #18 conductors is permitted on a 20 amp circuit. The smaller gage conductors need not be part of the fixture itself.
Click to expand...
You missed #1:
240.5(B)(2) Fixture Wire. Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(1) 20-ampere circuits — 18 AWG, up to 15 m (50 ft) of run length
(2) 20-ampere circuits — 16 AWG, up to 30 m (100 ft) of run length
(3) 20-ampere circuits — 14 AWG and larger
(4) 30-ampere circuits — 14 AWG and larger
(5) 40-ampere circuits — 12 AWG and larger
(6) 50-ampere circuits — 12 AWG and larger
Click to expand...
Click to expand...
Aye...

...But to elaborate, an 18AWG whip, according to 402.10(2), can only be used "for connecting luminaires (lighting fixtures) to the branch-circuit conductors supplying the luminaires (fixtures)" because, as stated in 402.10(1), fixture wire is permitted "for installation in luminaires and in similar equipment where enclosed or protected and not subject to bending or twisting in use..."

...And in any case, conductor ampacity is limited to 6A as in Table 402.5, because you'd have to use a fixture-wire type of conductor as listed in Table 402.3
 
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Smart $ said:
Aye...

...But to elaborate, an 18AWG whip, according to 402.10(2), can only be used "for connecting luminaires (lighting fixtures) to the branch-circuit conductors supplying the luminaires (fixtures)" because, as stated in 402.10(1), fixture wire is permitted "for installation in luminaires and in similar equipment where enclosed or protected and not subject to bending or twisting in use..."

...And in any case, conductor ampacity is limited to 6A as in Table 402.5, because you'd have to use a fixture-wire type of conductor as listed in Table 402.3
Click to expand...


Yes, you've summed it up nicely.:grin:
 
Cavie said:
How did the undersized sw leg noncence ever get started??????
Click to expand...

480sparky said:
By the same person who says you can't have wire nuts in a panel. ;)
Click to expand...

I can only say that if you were to undersize the wire and somebody else came along and decided to fish over from the load to a few other loads, you could burn up your wire. But that's assuming you added a significant amount of KW.
 
infinity said:
I would add that a field installed fixture whip with 6' of 3/8" FMC and #18 conductors is permitted on a 20 amp circuit. The smaller gage conductors need not be part of the fixture itself.
Click to expand...

True, but you cannot used those whips to daisy-chain fixtures.
 
Rich Elec. said:
240.5 (B) (2).
Fixture wire shall be permitted to be tapped to the branch circuit conductor of a branch circuit in accordance with the following:
(3) 20 ampere circuits - 14 AWG and larger.
Click to expand...
Yes, but switch-legs as part of the building wiring are not fixture wire, even if they supply fixtures.
 
Smart $ said:
. . . an 18AWG whip, according to 402.10(2), can only be used "for connecting luminaires (lighting fixtures) to the branch-circuit conductors supplying the luminaires (fixtures)" . . .
Click to expand...

. . . and not for connecting fixtures to other fixtures.
 
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