What does 240.5 (B)(2) allow and does anyone use it?

[MiElectrician]

To me it looks like I could pipe my lighting run to small offices and then run #18 mc (if it exists) to the fixtures. Also looks like large general office space could be piped to a box every 100 feet and then whipped with #18 mc.
I've never seen this done and assume that I'm misunderstand something but not sure what. Thanks in advance.

Mi electrician

 

[iwire]

To me it looks like I could pipe my lighting run to small offices and then run #18 mc (if it exists) to the fixtures. Also looks like large general office space could be piped to a box every 100 feet and then whipped with #18 mc.
I've never seen this done and assume that I'm misunderstand something but not sure what. Thanks in advance.

Mi electrician

See table 402.3 for list of conductors that are 'fixture wires'.

MC, NM etc are not in the list

 

[Dennis Alwon]

To me it looks like I could pipe my lighting run to small offices and then run #18 mc (if it exists) to the fixtures. Also looks like large general office space could be piped to a box every 100 feet and then whipped with #18 mc.
I've never seen this done and assume that I'm misunderstand something but not sure what. Thanks in advance.

Mi electrician

You cannot run 18 awg from the switch to the lights. The fixture whip can be 18 awg but not the rest of the branch circuit wiring.

 

[MiElectrician]

So none of the fixture wires come in anything like mc, so I'm guessing that I'd have to run flex and then feed tffn into it and this is why everyone just runs 12/2 mc.
Thanks for the quick response btw.

MI electrician

 

[Dennis Alwon]

So none of the fixture wires come in anything like mc, so I'm guessing that I'd have to run flex and then feed tffn into it and this is why everyone just runs 12/2 mc.
Thanks for the quick response btw.

MI electrician

Yep, I have seen fixtures wired from one to the other with mc but you cannot use the fixture whip to do this. Years ago we often got lay in fixtures without the whips so we had to make our own but we used metal flex with #12 wire....We probably could have used smaller wire but that was all we had on the trucks... Obviously if you are doing a large job it wouldn't pay to do that

 

[augie47]

The "answer" may lay here:
402.11 Uses Not Permitted. Fixture wires shall not beused as branch-circuit conductors except as permitted elsewherein this Code

 

[Smart $]

The "answer" may lay here:
402.11 Uses Not Permitted. Fixture wires shall not beused as branch-circuit conductors except as permitted elsewherein this Code

210.19(A)...

(4) Other Loads. Branch-circuit conductors that supply
loads other than those specified in 210.2 and other than
cooking appliances as covered in 210.19(A)(3) shall have
an ampacity sufficient for the loads served and shall not be
smaller than 14 AWG.

...


Exception No. 2: Fixture wires and flexible cords shall be
permitted to be smaller than 14 AWG as permitted by
240.5.

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

 

[petersonra]

What is the benefit of even doing this there's so little difference in cost between 14 + 16 + 18 that few feet wire just can't make that much difference cost-wise.

 

[Smart $]

What is the benefit of even doing this there's so little difference in cost between 14 + 16 + 18 that few feet wire just can't make that much difference cost-wise.

You can buy 18AWG fixture whips by the barrel. AFAIK 6' is the longest sold. I was told it saves only a little on material cost, but the cost savings on labor is significant. How true, I do not know.

Q: If a tap is permitted to 50ft., can one daisy chain 8 fixtures with 6' whips?

 

[lauraj]

You can buy 18AWG fixture whips by the barrel. AFAIK 6' is the longest sold. I was told it saves only a little on material cost, but the cost savings on labor is significant. How true, I do not know.

Q: If a tap is permitted to 50ft., can one daisy chain 8 fixtures with 6' whips?

I never actually thought about it before, but yeah, I believe you are correct.

 

[GoldDigger]

I never actually thought about it before, but yeah, I believe you are correct.

If you daisy chain the fixtures, all but the last whip would be branch circuit conductors, not taps to a single fixture.
JMO

 

[Smart $]

If you daisy chain the fixtures, all but the last whip would be branch circuit conductors, not taps to a single fixture.
JMO

Where in the pertinent sections (and exceptions thereto) are we limited to a single fixture?

I do not believe these tap conductors must meet the requirements of 210.19(A)(4) Exception No. 1 because #18 and #16 have an allowable ampacity of 6A and 8A respectively [402.5].

 

[GoldDigger]

Where in the pertinent sections (and exceptions thereto) are we limited to a single fixture?
.

More by inference than direct statement. If a feeder tap has to end at a single OCPD, a fixture tap should end at a single fixture.
The usage of the word "tap" in this section is unclear.

 

[Smart $]

More by inference than direct statement. If a feeder tap has to end at a single OCPD, a fixture tap should end at a single fixture.
The usage of the word "tap" in this section is unclear.

The only section passage which refers to these fixture wires as a tap is 240.5(B)(2)... which would be covered by the 240.2 definition of a tap conductors.

I'm aware of the underlying implications and would prefer something a bit more explicit.