ECN Forum Forums Code Related Discussion NEC & other Code issues cables in conduits/raceways

Is there anything in the NEC which prohibits installing cables--NM, AC, MC, TC, etc...in properly sized conduits? While I don't think it's a good practice to put some of these (like AC or MC) in a conduit, as long as it doesn't exceed the wirefill area for the particlar conduit, is it OK? I'm not concerned at this point with "why the heck would you want to put MC cable in a conduit?" This discussion came up at work, where we ran type TC cable in a tray and then went into a conduit for 100' or so on the outside of a building, then another 40' underground, then back up and into another building. I believe thee is no NEC prohibition to installing these types of cables in pipe as long as everything is properly sized, grounded and terminated.

There is nothing in the NEC prohibiting any cable from being installed in a conduit. As a matter of point only, there is a restriction on a conductor being installed in a cable tray...it must be 1/0 or larger.

I suppose that, while there is no direct prohibition, other issues can arise that make it a questionable practice.
That said, I can think of many valid reasons to run an assembly in a pipe...mechanical and environmental protection being first in mind.

When a conduit traverses several environments, it is usually considered to maintain a separate environment than the one it passes through. For example, EMT passing through a hazardous location is not considered part of the classified area.
A notable exception to this is conduit buried in the ground....this is considered a "wet" location, and some cables are not allowed in wet locations.

There is also the matter of grounding (or more correctly, bonding) the conduit. To properly do so, you would need to use a junction box- which makes it hard to understand why you'ld want to continue with a redundant raceway.

I got to say something, I can't help it. There are several cable and conductors that are not 1/0 or larger and are listed for use in cable trays.

Also putting a cable or conductor in a raceway because it is not suitable for a wet environment does not solve the problem. For example installing NM cable in conduit because it is not suitable for a wet location, does not change the location and should not be approved.

[This message has been edited by George Little (edited 03-22-2005).]

I always see folks posting about NM in a conduit related to a wet location. Like pulling it into a conduit along the outside of a dwelling. The argument is, the conduit is outside therefore a wet location?

I see Bell Boxes surface mounted with a GFCI in them all the time. Isn't the Bell Box a wet location?? Is it OK to use NM to feed said GFCI??

Walrus- I would see no problem with installing a surface mounted box on the outside of the building for a receptacle or lighting fixture and supplying it with NM cable as long as you are just popping out of the building and entering the back of the box. I do see a problem with running conduit in a wet location and then pulling in NM cable.

This forum is an awesome location for these types of questions and I'm sure we will get some interesting comments on this subject.

The 2002 (accidently) prohibits the practice. The 2005 permits it.

I don't see a problem with it either but
I do see the bell box as a wet location and if NM isn't suitable for a wet location then should it be allowed there even if its just popping in the back of box. Next I see a state inspector I'm going to pose this question and see what he says

I don't see a problem with a cable in a raceway, but I think you can run into some trouble when you get to a meter socket, box or a cabinet.

Check out 312.5(C) and the last sentence of 314.17(B). These seem to be requirements that apply to all cables and if the cable is in a raceway that connects to a box, then the requirement is met for the raceway but not the cable.

Tom

CRW
Your particular installation of type TC cable in conduit is expressly permitted!

336.10 Uses Permitted Type TC tray cable shall be permitted to be used in the following:
(2) In cable trays, or in raceways, or where supported in outdoor locations by a messenger wire.

I love the stuff. Any I've ever seen was also wet location and UV rated.




[This message has been edited by electure (edited 03-24-2005).]