Raceway or Free Air

[ML-LDS]

Is a 4" diameter nipple that is 8" in length considered to be a conduit? The scenario is that we have this 4" diameter, 8" long rigid nipple that allows passage of three conductors from one panel to another. Due to its short length, is this still considered to be a conduit (raceway), thus mandating the use of Table 310.15(B)(16) "Not more than three current-carrying conductors in raceway, cable, or earth..."; or can this be considered free air, since its length is so short?

 

[jeremy.zinkofsky]

Is a 4" diameter nipple that is 8" in length considered to be a conduit? The scenario is that we have this 4" diameter, 8" long rigid nipple that allows passage of three conductors from one panel to another. Due to its short length, is this still considered to be a conduit (raceway), thus mandating the use of Table 310.15(B)(16) "Not more than three current-carrying conductors in raceway, cable, or earth..."; or can this be considered free air, since its length is so short?

It is still a raceway but not subject to the same restrictions that conduit of length greater than 24" is i.e. conduit fill, reduction of conductor ampacity, etc. So for a length of conduit under 24" you can fill it to 60% and you do not have to upsize the conductors as you would for longer installations containing more than three current carrying conductors. See Chapter 9 Note 4.

 

[ActionDave]

What Jeremy said. 310.15(B)(3)(a)(2) is the code reference.

 

[GoldDigger]

Although you do not derate for over three conductors, you would still use the raceway rather than the free air base value

 

[ML-LDS]

Thanks Jeremy. I see what you mean about conductor fill. But it sounds like I will still have to size the three conductors based on ampacities listed in Table 310.15(B)(16) rather than the ampacities listed in Table 310.15(B)(17)...? I was trying to find somewhere in the code that defined the length of a nipple such that it was not considered to be a raceway. For example, would the use of a close nipple or chase nipple be reason enough to mandate ampacity sizing according to Table 310.15(B)(16)...?, or is the length of the close nipple (raceway) so short that it is considered negligible and thus allow ampacity sizing as if it were in free air Table 310.15(B)(17)?

 

[ML-LDS]

Thanks GoldDigger and ActionDave. I will size my conductors based on Table 310.15(B)(16).

 

[jumper]

Thanks Jeremy. I see what you mean about conductor fill. But it sounds like I will still have to size the three conductors based on ampacities listed in Table 310.15(B)(16) rather than the ampacities listed in Table 310.15(B)(17)...? I was trying to find somewhere in the code that defined the length of a nipple such that it was not considered to be a raceway. For example, would the use of a close nipple or chase nipple be reason enough to mandate ampacity sizing according to Table 310.15(B)(16)...?, or is the length of the close nipple (raceway) so short that it is considered negligible and thus allow ampacity sizing as if it were in free air Table 310.15(B)(17)?

Forget free air. It does not apply here what so ever.

Ampacity is Table 310.15(B)(16)

And as already stated, Chapter 9 note 4

(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) ad-
justment factors need not apply to this condition.

 

[jeremy.zinkofsky]

You're not going to find a loophole. Free air means free air. Like speaker wire or comm cables ran without any type of raceway. Even if you ran all of your conductors in tiny nipples from enclosure to enclosure, they will still be enclosed and not in free air.

 

[gadfly56]

Don't forget that the higher ampacity for free air conductors is about removal of heat. Once you put them in a raceway, it's harder to remove the heat. Done.