Fixture Whips

[Alwayslearningelec]

When using FMC as fixture tails is it usually 3/8" or 1/2"? Doubt it's ever 3/4". Thank you for the feedback.

 

[augie47]

90% of the fixture whips I see are "factory made" and all have been 3/8. I seldom see 1/2" unless someone is extending the wiring past the 1st fixture as a branch circuit.

 

[Tulsa Electrician]

If it is a spec job look it up in the spec book. Some will call out for minimum 1/2" unless it's a factory fixture whip. Some even talk about using MC as a fixture whip and any limitations of it's use if allowed.
Some specs will limit you to six feet no matter what.

 

[don_resqcapt19]

and if you are making your own, you will have to use a conductor that has an ampacity at least equal to that of the branch circuit, unless you use fixture wire.

 

[infinity]

99% of the ones we use are 3/8" X 6' long FMC.

 

[Tulsa Electrician]

and if you are making your own, you will have to use a conductor that has an ampacity at least equal to that of the branch circuit, unless you use fixture wire.

Good point.

 

[Alwayslearningelec]

and if you are making your own, you will have to use a conductor that has an ampacity at least equal to that of the branch circuit, unless you use fixture wire.

and fixture wire is called or abbreviated FNN or something like that???

 

[electrofelon]

and if you are making your own, you will have to use a conductor that has an ampacity at least equal to that of the branch circuit, unless you use fixture wire.

Any idea what the reasoning of this is? Why is an 18 awg fixture whip safe but one made from 14-2 MC on a 20A circuit not? Imo this is one of those things they should change instead of spending time on things like the new 1/4 conductor box fill allowance and the dimmer on each end of a hallway.

 

[ActionDave]

and fixture wire is called or abbreviated FNN or something like that???

You can use regular THHN. TFFN is for wire gauges smaller than 14AWG which you wouldn't be using anyway.

 

[ActionDave]

Any idea what the reasoning of this is? Why is an 18 awg fixture whip safe but one made from 14-2 MC on a 20A circuit not? Imo this is one of those things they should change instead of spending time on things like the new 1/4 conductor box fill allowance and the dimmer on each end of a hallway.

I agree. Plus there is that wacky tap rule for lights that lets you run like fifty feet of 18AWG or something like that.

 

[infinity]

We use #16 or #18 TFFN in our field made 3/8" fixture whips.

 

[don_resqcapt19]

Any idea what the reasoning of this is? Why is an 18 awg fixture whip safe but one made from 14-2 MC on a 20A circuit not? Imo this is one of those things they should change instead of spending time on things like the new 1/4 conductor box fill allowance and the dimmer on each end of a hallway.

No idea why...just what the code says. You have an opportunity right now to submit a PI to make a change. Remember that in general the code changes are made by code users who submit PIs.

 

[don_resqcapt19]

You can use regular THHN. TFFN is for wire gauges smaller than 14AWG which you wouldn't be using anyway.

That was the point of my comment. There is no reason not to make your own fixture whips using conductors smaller than the size of the branch circuit conductors. If you have a 20 amp lighting circuit, you can't make a fixture whip using 14 AWG THHN, but you can make one using 16 AWG TFFN.

 

[infinity]

If you have a 20 amp lighting circuit, you can't make a fixture whip using 14 AWG THHN, but you can make one using 16 AWG TFFN.

Another good example of a code section that needs a re-write.

 

[Rick 0920]

A lot of contractors today "daisy chain" their troffer fixtures. If you do this, you can't use the factory pre-made fixture whips unless the conductors have an ampacity of 20 amps. For example, if you daisy chained 30 troffers together, the whip between fixture #1 and #2 will see the load of the other 29 fixtures. I used to do this often because if your whips are 6' or less, Art. 330.30 (D)(2) allow you to run the whips unsupported which will save you lot of work not having to install your own ceiling wires.

 

[ActionDave]

That was the point of my comment. There is no reason not to make your own fixture whips using conductors smaller than the size of the branch circuit conductors. If you have a 20 amp lighting circuit, you can't make a fixture whip using 14 AWG THHN, but you can make one using 16 AWG TFFN.

I thought fixture whips were only legal because they were UL listed as a complete assembly and that you couldn't make your own out of parts.

 

[don_resqcapt19]

I thought fixture whips were only legal because they were UL listed as a complete assembly and that you couldn't make your own out of parts.

Nope, only because they comply with 240.5. There is nothing that restricts the use of 240.5 to manufactured assemblies.

 

[BarryO]

I thought fixture whips were only legal because they were UL listed as a complete assembly and that you couldn't make your own out of parts.

That's 240.5(B)(1). 250(B)(2) applies to field-assembled situations. It does seem a little nuts to allow 100 foot long "taps" in this case.

 

[ActionDave]

Fascinating. This is an area of the code I have glossed over forever. I'm both intrigued and annoyed. Someone is going to have to explain to me what is functionally different about TFFN and THHN that I can run 100 feet of 16AWG on a 20A breaker and I can't even run one foot of 14AWG.

 

[don_resqcapt19]

Fascinating. This is an area of the code I have glossed over forever. I'm both intrigued and annoyed. Someone is going to have to explain to me what is functionally different about TFFN and THHN that I can run 100 feet of 16AWG on a 20A breaker and I can't even run one foot of 14AWG.

Just a code rule ...no idea of how it got started or why. Been in the code for a long time. It was 240-4 in the 1975 code with the same language.