I have a 6/3 NM-B cable that is to be run through a Southwire Ultratite conduit to an external outlet for a generator. I plan to strip the cable prior to threading through the conduit: 1. for ease of passage; 2. for thermal issues. Just wondering what is the protocol for where the stripped section should start - just outside the conduit, or just inside? Also, the Ultratite fitting at the back of the outlet box has no provisions for clamping the wires in place. Can I presume then, that in this instance, clamping is not necessary as long as the wire is firmly anchored before entering the conduit run?

  • If you are running NM-B wire through conduit, you need to derate it because of heat concerns. Feb 21, 2015 at 5:30
  • It's a 6-3 cable and I'm planning to strip the outer sheath that surrounds the four wires.
    – Mark F
    Feb 21, 2015 at 5:45
  • 1
    @EricGunnerson Can you cite a source on that?
    – Tester101
    Feb 21, 2015 at 6:02
  • With only 3 CCCs in a 6-3 cable and with the sheath removed before running through the conduit, there should be no need to de-rate, correct?
    – Mark F
    Feb 21, 2015 at 6:17
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    @Tester101, EricGunnerson will not be able to find it because it does not exist. That is simply an urban legend code. Feb 21, 2015 at 13:44

2 Answers 2


There are (at least) two problems with this, and the solution to both is to change to THWN (or another wet-rated labeled conductor) when you change to conduit.

Problem one is that stripped NM is not labeled and not acceptable per code for that reason, as @Speedy Petey said.

The second is that you are running to an external location, which means that the conduit is by code defined to be a wet environment, and even with the sheath on, NM is not rated for wet locations, but you need a wire that is rated for wet locations.

  • 1) The NM outer sheath will be stripped only in the portion that runs through the 18" of conduit through the wall. It will be labeled along the remaining 20 ft of its length. 2) The Ultratite connections are designed to be waterproof (product name is actually "Liquidtight"), as is the outlet box (obviously). Therefore, this is not a wet/damp location.
    – Mark F
    Feb 21, 2015 at 15:28
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    It is defined, by code, as a wet location. There are no exceptions for the type of conduit. And it will, in fact be wet, if only due to condensation from the interior air hitting the cold exterior conduit, in which case a perfectly waterproof conduit just holds all the water inside.
    – Ecnerwal
    Feb 21, 2015 at 16:58
  • Thanks for the clarification Ecnerwal. I see your point here. I'm wondering how long it has been against code to run NM wire to outside outlets? My professionally installed hot tub and an outside outlet are both fed by NM cables!
    – Mark F
    Feb 21, 2015 at 18:05
  • @MarkF -- are you confusing NM-B with UF? Feb 21, 2015 at 18:14
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    If your hot tub is fed with any type of NM cable for ANY portion outside of the house that is also a major violation. Feb 21, 2015 at 20:53

i am assuming this is a USA install. once you remove the cable sheath you install it just like single wires if they are properly rated (at least as high as your peak voltage, usually 300 or 600 volts). there is no need to leave parts of the sheath on. if these wires are not rated or are not sufficient then you need to use real THHN singles or install it with the sheath all the way. i am not familiar with the type of conduit you mention. the uninsulated ground wire in metal conduit could be an issue (it can spread fault current to the conduit). you could buy a spool of green insulation THHN to replace any uninsulated ground wire with.

  • 1
    I'm not saying it is not done quite often, but buy code you CANNOT strip the sheathing off NM cable and then pull the wires in conduit. The internal wires of NM cable are not labelled and therefor cannot be used individually. Feb 21, 2015 at 13:39
  • See response to Ecnerwal's comment above
    – Mark F
    Feb 21, 2015 at 15:33

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