Sub Panel questions

[JOH]

Hey everyone. Long time lingerer, first time poster....

I want to start of by saying I am NOT an electrician and don't claim to be one! I know enough to be dangerous and "attempt" some stuff by myself and most is successful.

That being said, I had a new 30 x 40' pole barn built last fall and I am just now getting around to getting electrical service ran to it. So far, this is what I have been directed to (by friends and big box store employees) and just want everyones more proffessional opinions here to feel more comfortable before I start the project.

My barn is 120' from my main service panel on the outside of my house. It's a 200 amp main service. I'm planning to come off that with 100 amp breaker, feeding service to the barn with 2-2-4 Triplex Aluminum URD in conduit (2" probably and I know URD is direct bury but I want to be extra safe) along with a #8 THHN ground to connect the two panels to a 100 amp sub panel in the barn. I will probably never have the need for anything over 60 total amps but like I said, I always like to be safe than sorry.

Couple of questions;
1. Am I using the right service wire (2-2-4 aluminum and #8 THHN ground)?

2. I've read somewhere recently that you can't put URD on inside of structures. Is this right? If so, I assume I will need to splice it just outside in a junction box and bring in something else?

Probably alot more questions will arise from your answers but I'll start here and probably should have asked these questions to proffessionals before I went ahead and already purchased most of the stuff I mentioned!

I appreciate everyones input!

 

[pattenp]

# 2 Al can be over current protected to a max of 90 amps. URD is not allowed inside. You'd need to use a J-box outside to transition to SER cable for the inside. Mobile Home Feeder is allowed inside but needs to be in conduit.

Edit: Ether use MHF all the way in conduit or a combination of MHF and SER if you don't want to run conduit inside. Use 2-2-2-4 MHF and or with 2-2-2-4 SER, that will give you up to 90A.

The #8 ground, if copper is good for 100A. If the #8 is aluminum then it's only good for a 60A feed. If aluminum for 100A feed the ground needs to be at least #6.

 

[eddie1278]

URD is not a recognized building wire by the NEC. You can use USE with a dual rating that can go directly into the panel.

 

[JOH]

Thanks guys. Yeah, the #8 was copper, forgot to mention that.

I guess I'm not sure on the USE rating now. I'm not in front of the wire but I think I remember seeing "USE-2" or "USE-Type 2" on it???

If I had to go to 90 amp I could just put that size in my main from the house panel and still have the 100 amp in the sub right?

 

[pattenp]

The breaker in the main panel is sized to protect the feeder wire to the sub panel. The sub-panel can be rated more than the feed but not less. So having a 100A sub-panel be fed by 90A is okay. Also if the wire is only USE or USE-2 it cannot be inside of the house. You need to use THHN/THWN or XHHW or Mobile Home Feeder (RHH/RHW) wire to be able to run the wire from panel to panel. You can use the USE-2 for the outside but you will need to change over to a wire that is approved for inside use by splicing in a jbox on the outside just as you enter the structure.

 

[JOH]

Thanks for the info. I will plan on splicing on the outside in a jbox! Also, I assume I need to ground with 2 ground rods 6' apart outside also? I don't believe the cement guys left me any rebar to attach to but I can ask.

 

[pattenp]

If you don't have the ufer ground then you should sink 2 8' ground rods 6' apart. The electrode conductor needs to be one continuous piece of wire. #6 bare copper is what's commonly used. Also if the electrode ground wire is in a location where it may be subject to damage it should be placed in a conduit sleeve.