I may be mistaken but I think I have read that using NM wire (A.K.A. Romex) in conduits is forbidden by code. The reason I read was that in a conduit, it would not be able to dissipate the heat from the resistance inherent in all wiring.
Aside from the problem of pulling it through the conduit with bends, how is the heat buildup in a conduit anymore severe than running it in a wall completely surrounded by insulation? If anything, if the conduit were surface mounted, I’d think it would be better than buried in insulation.
Inquiring minds want to know 🙂
Teri
Replies
There is no restriction, I repeat NO RESTRICTION in using NM in conduit.
And there are not adjustments for heat build up.
For pulling NM through conduit it has to be figured as one big wire with the diameter the width of the NM. So that makes for fairly large conduit.
But that it does not have to be that big when it is only used to sleeve for protection. Such as a drop down a basement wall.
William the Geezer, the sequel to Billy the Kid - Shoe
Bill can repeat himself all he likes .... but this is a topic of considerable debate in the trade. This suggests that the answer isn't that clear.
Not that it really matters; "designing to code" is itself a violation of of the NEC; Article 90 specifically states the NEC is niether a design manual nor a DIY guide.
I'm pretty sure there's no law specifically prohibiting one from playing on the freeway while wearing a blindfold; yet that doesn't mean you should do it.
Cutting to the chase, Romex is it's own complete wiring method. If you want to change to another method - such as pipe - why not use materials intended for use with that method?
Also, contrary to Bill's assertion, running Romex in pipe can create situations that the NEC prohibits - such as running Romex in a wet location. Examine your reasons for wanting the pipe in the first place; chances are, this is a situation where you're not supposed to use Romex at all.
"Also, contrary to Bill's assertion, running Romex in pipe can create situations that the NEC prohibits - such as running Romex in a wet location."No, the problem is not caused by having Romex in conduit. The problem is caused by using Romex in none approved locations. But you would have the same problems using other wires not rated for use in wet locations.The problem is not the conduit, but the wire..
William the Geezer, the sequel to Billy the Kid - Shoe
Bill,I ran into what you spoke about in 2003 when I was wiring my Rastra ICF shop/apartment. The NM was run in the wooden floor system and then sleeved in EMT where it ran a short additional distance in a channel cut into the Rastra to reach the boxes. My inspector had a problem with the sleeving of the NM for heating concerns, and he wanted me to transition to individual conductors in the EMT. This would have peppered the ceiling with j-boxes and taken a longer time to do. However, he was okay with it when I explained that the EMT was only for very short runs at the boxes, purely for mechanical protection.When dealing with the AHJ, it sometimes matters a lot the way you describe what you plan to do.Bill
The International Electrical Code doesn't say NM cable in not permitted to be installed in conduit. It tells you what type of wire IS permitted to be installed in conduit and NM cable is not one of them. The UL (Underwriters Laboratory) has not approved NM to be installed in a "raceway" therefore the folks that write the codes, the International Code Council say "NO". It's all about keeping the wire within the temp. range of it's intended operating range by allowing air space around the wire.
You can either use to correct wire (THWN or THHN) or you can strip the outer jacked off the NM cable. The wires inside the "Romex" are THWN.
"International Electrical Code "Where is the International Electrical Code used? I have never heard of it..
William the Geezer, the sequel to Billy the Kid - Shoe
the last inspector I asked said if the run was 24 in or less he was ok with it... Longer he wanted a bushing on the end of the conduit to prevent mechanical damage and to strip off the sheathing.
I have the 2005 NEC in PDF form and searched for "24 in".And this here are the only 2 places that use 24 that might have any bearing on this.310.15 (B)(2)(2) Adjustment Factors
(a) More Than Three Current-Carrying Conductors in a Raceway or Cable.Where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables are stacked or bundled longer than 600 mm (24 in.) without maintaining spacing and are not installed in raceways, the allowable ampacity of each conductor shall be reduced as shown in Table 310.15(B)(2)(a). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor.But that says that if you have more than 3 current carrying conductors in a cable or more than 3 current carrying conductors in a conduit or more than 3 conductors or cables are bundled together then you need to derate.But, in most case we are talking about only 2 or 3 conductors so whether they are in a conduit or outside a conduit and bundled they aren't derated.The other place is in calculating conduit fill."(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)(2)(a) adjustment factors need not apply to this condition." That says for for 24" or less you can go to a higher percentage of conduit fill.Again that is the same regardless of if it is a wire or cable.Now the NEC very clearly states that CABLE can be used in conduit. But there are many different types of cable. But the NEC never references any specific types.Now this is the section on calculating conduit sizes based on fill."(2) Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage.Now this is from the handbook. It is not code, but explanatory information. "The maximum fill requirements do not apply to short sections of conduit or tubing
used for the physical protection of conductors and cables. Cables are commonly
protected from physical damage by conduit or tubing sleeves sized to enable the cable
to be passed through with relative ease without injuring or abrading the protective
jacket of the cable. The requirement of 300.5(D)(1) regarding physical protection of
direct buried cables and conductors as they emerge from below grade is an example of
conduit or tubing being used as a protective sleeve and not as a continuous raceway
system per 300.12. However, a fitting is required on the end(s) of the conduit or tubing
to protect the conductors or cables from abrasion. [See 300.15(C)."This would be what is typically used to sleeve a run down a basement wall. And this is how you treat a CABLE when calculating conduit fill.If you could not put cables in conduit then this would not be their."(9) A multiconductor cable of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter."Now here it specifically allows for NM to be run in conduit for protection.300.15 Boxes, Conduit Bodies, or Fittings — Where Required...
Where the wiring method is conduit, tubing, Type AC cable, Type MC cable, Type MI cable, nonmetallic-sheathed cable (NM), or other cables, a box or conduit body shall be installed at each conductor splice point, outlet point, switch point, junction point, termination point, or pull point, unless otherwise permitted in 300.15(A) through (M).
...
(C) Protection A box or conduit body shall not be required where cables (of which NM is one type specified) enter or exit from conduit or tubing that is used to provide cable support or protection against physical damage. A fitting shall be provided on the end(s) of the conduit or tubing to protect the cable from abrasion.And from the handbook."Section 300.15(C) permits conduit or tubing to be used as support and protection
against physical damage without terminating in a box. It also permits conduit or tubing
to be used as physical protection for underground cables that exit from buildings or
that are located outdoors on poles, without a box being required on the end of the
conduit. A fitting to protect the wires or cables against physical damage is required on
the ends of the conduit or tubing.".
William the Geezer, the sequel to Billy the Kid - Shoe
>>>Where is the International Electrical Code used?Indeed. What is IEC?I've used NM inside conduit in many situations, mostly to protect conductors from mechanical damage. It would have been really messy and unsightly to transition to THHN.None of my inspectors had a problem with this.Scott.
I personally have never read that you are not allowed Romex in conduit. Then again I have never looked because it is something that we NEVER do out in the field, probably for the same reasons others have mentioned. We ALWAYS transition to individual conductors by stripping the jacket and using the appropriate change-overs.
If anyone can share the section of the Codebook that references this, please share with the rest of the class. This thread has ratcheted up my curiousity.
"We ALWAYS transition to individual conductors by stripping the jacket and using the appropriate change-overs.""310.11 Marking
(A) Required Information
...
(B) Method of Marking
(1) Surface Marking The following conductors and cables shall be durably marked on the surface. The AWG size or circular mil area shall be repeated at intervals not exceeding 610 mm (24 in.). All other markings shall be repeated at intervals not exceeding 1.0 m (40 in.).(1) Single-conductor and multiconductor rubber- and thermoplastic-insulated wire and cable(2) Nonmetallic-sheathed cable
...If you strip the sheathing then you remove the markings.Although it is only for a section that you can see anyway. But a inspector that want to hang you, but can't find an "real" problem could call that out..
William the Geezer, the sequel to Billy the Kid - Shoe
Thank you gentlemen,
Even if some of you don't think some of the other respondents are gentlemen :-)
I only asked the question as I got to thinking about the alleged problem with heat buildup.
If I may ask, if the wire (circuit) is so loaded as to have significant heating from the current for the wire size, then NM (aka Romex) buried in insulation can't be good either? But I suppose there is some code de-rating for that situation.
I wasn't planning to actually put NM in conduit except for a sleeve in areas where there is potential mechanical abuse. Several answered that question, so thank you.
-- Teri