I’m putting in a 50amp RV receptacle about 60’ from the meter. Planned on using 6/3 W ground buried in pvc conduit. Is it better to use the NM-B with stranded wire or the UF-B under ground wire that is solid? The UF is slightly cheaper.
I thought you were supposed to use THHN.
I’m thinking UF-B cable w/o conduit. Interested in seeing what those that know say. 
For any buried circuit, you should always use an underground-rated cable. Putting it in PVC will help keep the gophers from chewing on it.
While the UF might be a bit harder to work with, it will stand more ground shift and seasonal freeze/thaw expansion/contraction. And it's waterproof, unlike the NM.
While the UF might be a bit harder to work with, it will stand more ground shift and seasonal freeze/thaw expansion/contraction. And it's waterproof, unlike the NM.
To me, it depends on the depth I'm willing to bury (trench). e.g. PVC @ 18in or UF @ 24in. Minimum #6/3 solid wire regardless. If not UF, then THWN in conduit. If using UF without conduit, transition from depth to above ground box with conduit. Others may not agree but that's OK.
NM-b isn’t rated for burial
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KOPET, response #5 in my opinion is correct. UF is a harder to work with. The WP stiff jacket is tougher than NM or individual THHN, but applicable for your project. Try and back fill with minimal rock or debris as settling, heavy equipment or freezing can potentially damage it long term.
If you decide to go with thwn or hhn, let me know. I bought big spools of 6 gauge of it from a guy on here I think about 7 years ago. Have a ton. I can pull off 4 70ft runs for you. Not sure if I have enough green but probably do for 70ft. Otherwise you can use white like I did for ground. I have black, red, white and green. I made a 150' extension cord in flexible conduit that has worked great for many years. Before anyone says anything yes I accounted for voltage drop in that distance.
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No drop at that distance to be of concern.
And conduit buried is consider wet location and should have THWN, The W for wet location. Most THHN is dual rated but.... Any electrician will tell us that buried conduit will collect condensation. UF would fine of course. No Romex in buried conduit. 2008 code anyway.
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