Nipple Derating Factor code reference 310.15(B3A)(2)

[Brian Baker]

If someone were to run two conduit pieces from a panel box to an LB or similar point and the conduit does not exceed 24 inches going into and out of the LB does this code reference still apply?

 

[infinity]

If you have a nipple 24" or less there is no derating required. Every pull point starts the 24" measurement over so if you had a 24" nipple into an LB and then into a 24" nipple, no derating would apply. If you had a coupling where the LB is then derating would apply.

 

[Carultch]

If you have a nipple 24" or less there is no derating required. Every pull point starts the 24" measurement over so if you had a 24" nipple into an LB and then into a 24" nipple, no derating would apply. If you had a coupling where the LB is then derating would apply.

So does this mean that one could theoretically build a 20 ft run, with C-bodies every 2 ft, and still take credit for the 24" no derate rule? Not that one would do that in practice, since I can't think of an example where it would be cost-effective, but it would still comply with the NEC.

I take it that the possibility for a setup like that is more of an oversight in the NEC, than any physical reason why it would be safer than the same conductors in a 20 ft continuous run. I can see a physical reason why this would be allowed, considering the conduit fill percentage rule.

 

[packersparky]

If you have a nipple 24" or less there is no derating required. Every pull point starts the 24" measurement over so if you had a 24" nipple into an LB and then into a 24" nipple, no derating would apply. If you had a coupling where the LB is then derating would apply.

Here a LB (or any condulet) is not considered a "similar enclosure" as boxes or cabinets and derating would apply to the installation you describe.

(4) Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(B)(3)(a) adjustment factors need not apply to this condition.

 

[Brian Baker]

Would that mean using any juntion box would reset the count? Not that this would be cost effective.

 

[infinity]

Here a LB (or any condulet) is not considered a "similar enclosure" as boxes or cabinets and derating would apply to the installation you describe.

(4) Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 in.) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and 310.15(B)(3)(a) adjustment factors need not apply to this condition.

310.15(B)(3)(a)(2) is the section applicable to my last post. If you have 24" raceways joined by a conduit body or a box the raceway has not exceeded 24".

310.15(B)(3)(a)(2) Adjustment factors shall not apply to conductors in
raceways having a length not exceeding 600 mm (24 in.).

 

[packersparky]

310.15(B)(3)(a)(2) is the section applicable to my last post. If you have 24" raceways joined by a conduit body or a box the raceway has not exceeded 24".

Here 310.15(B)(3)(a)(2) is applied in conjunction with Note 4 to Table 1 of Chapter 9 which I included in my last post. The note to the table is interpreted here to say that a condulet is included as part of the raceway system as it is not a "similar enclosure" to a box or cabinet. The definition of "conduit body" seems to support this view. That is the way it is viewed here, YMMV.

 

[ggunn]

So does this mean that one could theoretically build a 20 ft run, with C-bodies every 2 ft, and still take credit for the 24" no derate rule? Not that one would do that in practice, since I can't think of an example where it would be cost-effective, but it would still comply with the NEC.

As Jurassic Park has shown, just because something is possible doesn't necessarily make it a good idea.

 

[Adamjamma]

unfortunately, I have seen this one done in the early eighties, in Virginia. Every 24 inch nipple went into a 4 inch box... all the way down a 14 foot wall, and had around 20 wires stuffed in them... all with blank plates as well.

My boss was looking at the job and told the owner we would have to rip that out and put in proper conduits for the wire...

We did not get the job. Owner thought it was just fine. In fact, he felt we could run our extra wires through it no problem because he could fit an extra wire in it...

Boss told me in the truck on the way home, idiots like that you walk away from..they are a fire waiting to happen...

 

[infinity]

Here 310.15(B)(3)(a)(2) is applied in conjunction with Note 4 to Table 1 of Chapter 9 which I included in my last post. The note to the table is interpreted here to say that a condulet is included as part of the raceway system as it is not a "similar enclosure" to a box or cabinet. The definition of "conduit body" seems to support this view. That is the way it is viewed here, YMMV.

I can see your point but IMO that list doesn't override 310.15(B)(3)(a)(2) which only mentions the length of the raceway.

 

[sameguy]

Let me get this, to save money, we need to add material and labor as opposed to running two pipe runs.
I would bid against that person all day long!

 

[jaggedben]

It isn't the 20ft run that presents a condundrum. It's the situation where, say, you want just two nipples with an LL to get out of a box and up the wall 24", and there's stuff in the way that prevents two smaller raceways from going in.

 

[wwhitney]

It's not immediately clear to me from the Article 100 definitions whether a conduit body is a raceway. Here are the 2017 definitions:

Conduit Body. A separate portion of a conduit or tubing system that provides access through a removable cover(s) to the interior of the system at a junction of two or more sections of the system or at a terminal point of the system.

Boxes such as FS and FD or larger cast or sheet metal boxes are not classified as conduit bodies.

Raceway. An enclosed channel designed expressly for holding wires, cables, or busbars, with additional functions as permitted in this Code.

Cheers, Wayne

 

[jaggedben]

It's not immediately clear to me from the Article 100 definitions whether a conduit body is a raceway. Here are the 2017 definitions:



Cheers, Wayne

I don't think that's the question. I think the question is whether a conduit body is a 'similar enclosure'as compared to a box or cabinet.

 

[wwhitney]

I don't think that's the question. I think the question is whether a conduit body is a 'similar enclosure'as compared to a box or cabinet.

That would be true if you believe that Chapter 9 Table 1 Note 4 overrides 310.15(B)(3)(a)(2).

Otherwise, the only question is whether a conduit body is a raceway or not. If it is, then you include its length when measuring the raceway length. If it is not a raceway, then you measure raceway length between conduit bodies.

Cheers, Wayne

 

[infinity]

That would be true if you believe that Chapter 9 Table 1 Note 4 overrides 310.15(B)(3)(a)(2).

Otherwise, the only question is whether a conduit body is a raceway or not. If it is, then you include its length when measuring the raceway length. If it is not a raceway, then you measure raceway length between conduit bodies.

Cheers, Wayne

I agree. 310.15(B)(3)(a)(2) stands alone without the chapter 9 reference. IMO a conduit body is not a raceway but the Article 100 definition is rather poor at stating that one way or another.