Cable type required for underground

[John Sheets]

Folks,
I won't bore you with all the details, but I simply need to know if cable that is run underground in PVC conduit, joints glued together, from house to garage, is required to be "underground feeder" or.... since the conduit is there, is it OK to use the standard plastic sheathed Romex type stuff that you would normally use indoors. None of the cable would be exposed, completely encased by the conduit for the entire run.
Thanks, JS

[Robert Reece]

If you run either in conduit you have to derate the amp rating because you essentially have 2 conduits. I think the correct way to do it in conduit is run individual conductors. You could achieve this by just stripping the romex, or you can buy lengths of wire in whatever guage you need. If you use the same color wire for all your conductors, just mark the ends with different color tape before you pull them.

[Joe Chritz]

THHN is fine but I think there is slightly less expensive wire you can use.

T90 maybe, I am not an electrician nor did I stay at a Holiday Innn Express.

Joe

[Rollie Meyers]

THHN is fine but I think there is slightly less expensive wire you can use.

T90 maybe, I am not an electrician nor did I stay at a Holiday Innn Express.

Joe

THHN cannot be used underground as it's considered a wet location & THHN is for dry locations only, what is needed is a dual rated THHN / THWN rated cable for a wet location. The NEC considers conduits underground & outdoors to be wet locations.

[Lee Schierer]

Despite your best efforts, the pvc conduit may leak. I would use direct burial rated cabling and make sure the wire size is large enough for the run length and anticipated load.

[David G Baker]

I put 25 feet 2" PVC conduit underground and pulled my #2 direct burial wire through it. I had measured wrong and the wire was 10 feet short. I pulled the wire back out of the conduit, it was very wet. The wetness really surprised me because the weather was fine, no rain, no mist and the humidity was average. I had capped the ends of the conduit prior to letting the conduit set over night to keep out any chance of critters or moisture getting in the pipe. The only thing I can think of is condensation from the warm outside air and the cool underground temperature causing the wetness.
I would use underground wire in conduit and individual strands of the required sized wire. You don't really need the conduit, I use it because I frequently dig holes and don't have the memory that I once had. DAMHIK

[Rob Russell]

If you run either in conduit you have to derate the amp rating because you essentially have 2 conduits. I think the correct way to do it in conduit is run individual conductors. You could achieve this by just stripping the romex, or you can buy lengths of wire in whatever guage you need. If you use the same color wire for all your conductors, just mark the ends with different color tape before you pull them.

It is acceptable to pull a cable assembly through conduit. If this case it would mean something like UF - Underground Feeder cable because the cable has to be wet location rated and normal Nonmetallic Cable doesn't carry that rating.

There is something you have to do when when pulling cable through conduit - make sure that the conduit is sized appropriately. When you pull a multiconductor cable through conduit, you have to take the cross-sectional area of that cable and use that to calculate conduit fill. If the cable is elliptical (such as UF), you need to use the longer diameter as a circular diameter when you calculate how much space the cable takes up.

[Roger Frazee]

It's not clear to me what you are doing. Are you running a feeder to a sub-panel in the garage or just a 120 volt line for lights and receptacles.

Don't pull a multi wire cable like uf-b and as already said no romex. Use individual wires intended for underground wet location and conduit.

[John Sheets]

It's the latter. Just for some receptacles that won't be used often, lights, and garage door opener.

[Roger Frazee]

Hi John

I'm sorry I had to leave for a bit. If this is just a branch circuit of 120 volts you want to get some copper 12 awg thwn and a 20 amp breaker. Be aware of long distances though as voltage drop can at times be a concern. At the big box most thhn is dual rated as thwn or thwn-2. Get some black, white and green. It will be stranded wire not solid. Use this it will pull easily through the conduit. Land it on a snap switch for your required disconnect. Then from it wire your switches for lights and also your receptacles. If you want to get 2 20 amp branch circuits to the garage you can do what is called a multiwire branch circuit. If that is something you would like we can tell you how to do that also. You are also allowed to run a 3 way switch loop to the garage for outside lights if you want. Remember gfci for your receptacles out there.