I know that gray, UF-B outdoor 14/2 electrical cable can be used both outdoors and indoors for permanent installations in Michigan. Why isn't the outdoor cable ALWAYS used for ALL 15amp indoor wiring then?

The outdoor cable can do so many more things than the indoor.

Outdoor cable is: 25%-50% cheaper. (Wow!) Is highly resistant to acids, alkalis, corrosives, chemicals, lubricants, fungus, water, UV, and can be directly buried underground. Sheds, garages, barns, etc.

Both in/out door 100' reels are copper. 100' of the indoor weighs 6.1#. The outdoor weighs 6.5#.

I don't see the downside. Just the drastic lower price is enough to use it everywhere indoors and out. What am I missing? Why would the far better/safer/durable cable be so much cheaper... and NOT used everywhere 14/2 15amp is needed?

Update: 3 different DIY store employees didn't have an answer. But they found their manager that "knows all about wiring". He said you CAN use the outdoor wiring, indoors... but the building inspector would immediately raise a red flag due to the gray coloring... and give you a headache about it.

(I would think the inspector would only say "wow, you guys used the far better product than needed. Excellent job.")

  • Does it come in different gauges? Grey colour does not mean much, what is the label/writing on the cable? 14/2 can only be used up to 15 amp circuits, nothing bigger. Michigan electric code might allow it, but might not be allowed in other places for indoor/outdoor use. Sounds more like extension cable(not for permanent use).
    – crip659
    Jul 31 '21 at 14:25
  • It's permanent UF-B (Romex style)... just like the white stuff.
    – TammyTech
    Jul 31 '21 at 14:32
  • 1
    Reading up on UF-B, seems like the only reason it is not used more is that it is usually more expensive than NM-B. It being 25 to 50% cheaper might be a good sale or a mistake. Is it copper wire or aluminum wire? Aluminum wire that size needs special connections/devices made for aluminum wire.
    – crip659
    Jul 31 '21 at 14:46
  • @crip659 Yeah, something is "off" here. UF is always more expensive, unless, like you said, a silly sale, or a pricing mistake. + Jul 31 '21 at 14:53
  • 4
    I suspect that you've found an arbitrage opportunity. My guess: ordinary NM-B is flying off the shelves and gets re-stocked at higher prevailing prices. UF-B doesn't move as fast, so hasn't been restocked recently, and thus doesn't reflect crazy new material prices as quickly. Jul 31 '21 at 20:33

In my neck of the woods, 14/2 UF is $99.00 for 250 roll, 14/2 NM is $85 at Home Depot. Still outrageous prices now, but hopefully they'll come back to earth. So I certainly haven't found the same pricing as you have.

Back to your question. UF is a total PITA (Pain in the A**) to work with. It's hard to strip, is stiffer than NM so makes it hard to pull. I don't know if the NEC has anything to say about running UF for interior circuits, perhaps some of the experts here could chime in.

  • On another forum, seems like striping is more based on the maker. Some is supposed to nicer than others, these days.
    – crip659
    Jul 31 '21 at 15:34
  • Additional PITA features if you need to pull through conduit besides incredible friction of pvc you have to calculate conduit fill as a round cable of greatest dimension of cable resulting with large conduits. Also a possible derating concern where most UF is sold as "UF-B", the "B" indicating 90°C conductors I don't see the 2020 NEC recognizing the "B", not allowing derating calculations of conduit/penetration/cable 24" long grouping based on greater than 60°C which would normally limit you to 3 current carrying conductors. Aug 1 '21 at 16:17
  • When they ran the UF down to my dock, they brought it all the way in through the crawlspace (40 or 50 feet) and tied it into the NM coming from the circuit breaker panel in a junction box in the crawlspace. They also ran a separate Uf from the dock through the crawlspace up to a 3-way light switch in the living space in order to control the dock lights.
    – SteveSh
    Nov 30 '21 at 16:18

UF-B doesn't come in some configurations

Good luck finding /4 or /2/2 UF-B -- it simply isn't made! On the other hand, there is nothing wrong with using some spare UF of the correct gauge and wire-count for an indoor run, and this might be desirable in a crudely roofed shed or utility space that's only barely "indoors".

Pricing varies

Your experience with UF being vastly cheaper than NM sounds like a local anomaly, otherwise people would do as you say. Normally, NM is somewhat cheaper as it uses somewhat less material for the jacketing, and is also easier to work with due to the ability to use a paper separator between the jacket and the insulated wires inside.


It's not just about the "per-foot" cost

Yes, anywhere NM-B is required, UF-B is allowed. So, "#14 NM" is a size you don't need to buy.

The way I see it, it's not just about the material cost per foot. It's also about the capital you have tied up in the fractional spools of material. And part of the problem here is that pricing is setup to be significantly cheaper when you buy larger spools, so you have to buy 250' spools of everything just to pay a non-outrageous per-foot price.

"Perfect world" you have 12 spools: 14/2, 14/3, 12/2, 12/3, 10/2, 10/3, all in both NM and UF. And since buying them in <250' spools is not cost effective, go price those 12 spools in 250' lengths. That's a lot of capital to tie up!

So buying the perfect wire for every task is just not cost effective unless you're wiring a house a week.

I actually take it a step further. Anywhere #14 is required, #12 is allowed. I don't stock any #14 wire.

But that's a pricing glitch

It's either a discount-store fluke, or a temporary "run on" building materials, or an error in your source data. UF is more expensive because the insulation and sheathing is more complicated. If anything, shortages and the building craze is drying up NM, since people aren't wise to the fact that UF will suffice.

  • 1
    Harp, I think the OP is right, I did some pricing research and it's all over the board, it's insane, in some cases UF is less expensive than NM, I checked both Lowes and HD and got similar results, but what really blew me away is both are pricing 1,000' of 12/2 NM at over a thousand dollars. HOLY COW. Aug 1 '21 at 15:22

I'm not sure who I'm suppose to up-vote as the 'correct answer' here. Several people had various good answers... others gave additional info that was also very helpful (for things I didn't even think about). And I assume I can't up-vote a "comment", only an "answer".

Aloysius Defenestrate wins it for his suggestion (but in a comment). It does indeed look like the lower price was due to higher copper prices (Home Depot even had a makeshift sign taped to their shelf). Perhaps the lesser used "outdoor cable" was store inventory from months before the price increases. While the much used "indoor cable" was newer stock, at its newer higher prices.

And a thank you to George Anderson for the stripping suggestion. Outdoor may be harder to strip. I've never tried it... but it looks like part of the difference between the 2 cables are:

  • Indoor has its white outer insulation bundled loosely around all 3 conductors.
  • Outdoor has its gray outer insulation bundled tightly around EACH of the 3 conductors, individually. (Probably to avoid an airspace where water could gather.)

Wrong answers: It's not "an extension cord". It's not due to being the wrong gauge, nor aluminum wire, nor the wrong amp rating. It wasn't a pricing error, not a huge sale.

100' copper 14/2 indoor white: $86
100' copper 14/2 outdoor gray: $56
  • Hi TammyTech: I think you were right (see a recent comment re: pricing). It's absolutely INSANE right now, nothing makes sense. UF has always been more expensive than NM, until now. And even the number of feet in a coil now changes the equation a lot. Totally market driven pricing, it'll change. When I built my house, I was paying about $120 for a 1,000' spool of 12/2 NM. A couple of years later, it jumped to $400 during a shortage and I was outraged. Now Lowes and HD are selling 1,000' spools of 12 for over $1,000. NUTS, JUST NUTS. Aug 1 '21 at 14:58
  • Oh, and BTW, you can upvote comments. I think it only gives the commenter a point or two, but it's a nice way to show your appreciation for the comment. Aug 1 '21 at 15:29

From my experience, underground UF-B is generally more expensive as the jacket material is more expensive to make. Currently, many big box stores have the UF-B marked less than the NM-B cable. That's because the price is not as inflated from demand like NM-B. NM-B is also used more frequently because it is WAY easier to work with. Wire prep 50 outlets with some good romex cable then try to do the same with equivalent size UF-B and it will be easy to see why underground cable is not typically used indoors. However, I am tempted to buy some myself for a 100ft run from my panel to an RV outlet on the outside of my house. 50ft of it will be indoors so my previous plan was to buy romex 50' NM-B for around $50 and use individual wires in conduit for the outdoor portion. Now, the indoor NM-B is nearly 3 times the cost it was when I first priced it and I can do it cheaper with underground cable.

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