THHN versus NM for conduit wiring?

Question

I am wiring a small workshop, using conduit. I was shocked to see how expensive THHN/THHW cable is, with respect to NM-B: at local big-box store, 100ft of 14/2 NM was $33, whereas 100ft of THHN was about $20 (so $60, almost double the price of NM, for 2 conductors plus EGC).

I am wondering about the pros and cons of using NM instead of THHN. Issues I see, for various options, are as follows:

1. Just run exposed NM ? Probably against code, but it's just a detached shop and won't be inspected. I'm using conduit for outlets, but this is for lighting wiring in the ceiling, so out of reach; OTOH, it might be tempting to hang things on it. Probably a terrible idea.

2. Run NM inside conduit ? Might be tough, due to its stiffness. OTOH, I'm using pretty big conduit (3/4" for just 2 14ga conductors plus EGC) and only two bends max.

3. Pull the conductors out of the NM jacket and use these in the conduit ? How difficult would this be ? Don't want to have to rip the jacket the whole way, but once one conductor is pulled out (probably the EGC) the others should be easy. I've heard varying opinions on whether the wire inside the jacket of NM is actually THHN. I've read it doesn't have as "slippery" insulation, so doesn't pull as easily as real THHN. I've also read it's un-marked, so technically against code, but I probably don't care.

4. Bite the bullet and pay much more for real THHN.

5. Use armored cable such as MC or BX.

Answer 1

I pay $48-52 per 500ft for #12 THHN/THWN-2. I do not use #14 at all.

My preferred supplier is City Electric, and I shop around other proper electrical supplies, and Menards on 11% off days.

I do not buy ground wire because I use EMT properly, I use enough conduit clamps to hold it where it belongs, and I refrain from routing it unguarded in places at risk for damage or pullout.

When I find an odd situation where I worry about EMT parting, I dive into my junk drawer and find some old solid THHN or Romex that I had pulled out earlier, and strip down a bare wire of enough length to link the two junction boxes on either side of the danger zone.

By the way, I use stranded THHN/THWN-2. After the pleasure of working with stranded THHN/THWN in conduit, the idea of choking NM down a conduit is laughable.

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You cannot strip the sheath off NM as a "cheap" way to get THHN. The reason is obvious once you work with the various wire types, but NM wire insulation doesn't even begin to compare to THHN insulation and it will too easily take damage. You are also relying on being able to strip sheath 100% perfect with no damage to either black or white insulation. It is also not marked, so it is not legal to use. And then you only have solid wire, which is more alligator wrestling.

The other big problem with shucking NM is you are stuck with only 2 wire color choices. I stock 9 colors of THHN and 10 colors of tape. If you're buying just a few rolls of THHN, consider colors other than white black red.

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1. I don't know whether running exposed NM is legal in your shop. Conduit is very convenient for lighting. Do not hang anything on electrical cables or conduit. If you want hangers for low voltage wiring or anything else, put them up there while you're up there.
2. Your statements are inconsistent: one hand is hanging oversized conduit and running superfluous ground wires, the other hand is wringing over the cost of wire. Make up your mind. Either you're trying to save money or do a good job. I wire my lighting grids with 1/2" EMT and 2 THHN wires. Easy peasy.
3. As mentioned, individual wires inside NM will get damaged if pulled through conduit.
4. If THHN is much more expensive, you're sourcing at the wrong place. The big-box stores really getcha on small reels, and shamelessly overcharge on most other electrical parts too. (just not the ones you're likely to price-check). Big-box are not gods of pricing, or even selection; they are gods of being open at 9:30pm on a Saturday. They also have some freakish "Pied Piper" effect on consumers; it's almost impossible to convince folks to stop shopping at big-box.

Answer 2

Option 6: shop somewhere that is not going to rip you off on something as basic as 14AWG THHN.

Your intuition that NM and THHN should be priced similarly per wire-foot (length of cable * number of conductors in cable) is indeed correct -- the copper content is the main driver of the price of the finished product. (At an online supplier I use as a pricing reference, 14AWG THHN is 9 cents to the foot, while 14/2 W/G NM is 25 cents to the foot.)

So, we can conclude from this data that the big-box store is ripping you off on the THHN. As Harper suggests, an electrical supply house won't do that to you, so I would suggest finding one local to you and asking them for a price instead.