OT - NM-B Wire

61-4010 · Nov 5, 2011

Need to run a 50A 240V circuit outside to a spa. From the main panel, it will be 50A then once it goes to the spa panel outside, there will be a GFCI breaker. The run is about 80 feet....about 2/3 will be under the house in the crawl space and 1/3 outside running along the deck. All will be encased in watertight conduit.

Can I use NM-B wire for this since it will be all in watertight conduit?

dr sportster · Nov 5, 2011

I'm not looking in the code book.Usually I just make up some hairbrained answer so here goes. Normally RX does not go into pipe. Almost every buried pipe will get water inside . That cable you spec has paper inside that gets wet and and the copper will slowly [very, very slowly] detiorate. The proper cable would be UF . If you use UF you don't need the pipe. However it is fine to sleeve it if you desire. I have seen inspectors not wanting UF to be brought through the house and wanted a transition made to RX once entering the home . This is an utterly ridiculus requirement.But ...

Rick Kr · Nov 5, 2011

Agree with Sportster.

I always use UF outside. Depending on location, I put it inside conduit also, adds a little more protection from a stray shovel.

Also, if it is underground, it will get wet, or at least quite moist. Based on everything I have dug up.

Rick

LJD · Nov 6, 2011

You're talking #6 copper if using Romex and shooting for a 2% voltage drop..

If I was doing the job, I'd use some version of USE or URD aluminum in conduit. You can go to Home Depot and buy it by the foot, often cheaper then at a wholesale electric store.

I suspect you'll find the #4 aluminum USE or URD "underground service entrance" or "underground residential distribution cable" cable cheaper then #6 UF copper. #4 URD would do the job just fine.

I just installed some underground circuits using 2-2-4 URD cable from Home Depot. Normally it would be $1.08 per foot, but they sold it to me for 60 cents per foot since it was a remnant "end of reel" item. I'm not sure what the 4-4-2 costs right now.

OT - NM-B Wire

61-4010

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dr sportster

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Rick Kr

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LJD

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