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underground wiring

Posted by charlie67 (My Page) on
Thu, May 17, 12 at 4:54

I want to run two runs of underground wire from the house in pvc conduit. One run will be approx 100 ft to an outdoor receptacle located on a wooden fence line, and the other run will go to a barn approx 200 ft from the house. I would like to run both runs in one pvc conduit. How best can I accomplish this? Can I buy a "T" to split off the conduit? i am working with #6 wire for the barn run. I want to try and avoid making 2 separate runs of conduit if feasible.


Follow-Up Postings:

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RE: underground wiring

Well a T in the plumbing sense wouldn't work. What you would need to do is put a junction box in at the point the split would be. Remember that anything underground (even in conduit) is a wet location so make sure your conductors and whatever else are rated for that.

The barn will most likely have special requirements as well. It sounds like with #6 you're planning multiple circuits out there. You'll need ground rods, appropriate disconnect, etc... You must run four conductors (two hots, neutral, and ground) to such a structure. Depending what's in the barn, there may be other requirements.


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RE: underground wiring

Tell me this jct box would it be located above ground on some sort of pole? would I use a pvc outdoor type?


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RE: underground wiring

It could be IN the ground for all it matters.


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RE: underground wiring

If there are no splices or other connections in the junction box, underground is OK.


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RE: underground wiring

"If there are no splices or other connections in the junction box, underground is OK."

Even if there ARE splices in the JB it can be underground.

It is just a little harder to make secure connections.


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RE: underground wiring

As I said, everything that's underground needs to be approved for wet locations. If you place the box in the ground, you can splice there but you have to use an approved splice (i.e., not regular wirenuts).


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RE: underground wiring

the wire insulation is marked rhh-2 and rhw-2. what does that mean? is it ok for underground in pvc conduit?


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RE: underground wiring

RHW-2 is 90C rated for both wet and dry locations. It should be OK.
There's no such thing as RHH-2 to my knowledge, just RHH (not that it matters here).

Note that you need to derate the ampacity of the conductors because you have more than three current carrying conductors in the same conduit. Of course, with 200+ foot runs you may wish to size up the conductor for voltage drop reasons anyhow.


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RE: underground wiring

Thanks for the info. I have #6 wire to run. Considering I will be making a 200 ft run with one set (3wires to power a 20amp gfi outdoor receptacle)and 4 #6 wires to power the barn with 220v,nuetral, and ground at a distance of 300ft. what breaker size will I need to use at the main box in the house for the barn run? My distances are more than I stated in my first post. My Bad!!! Thanks


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RE: underground wiring

What power requirements do you have in the barn?

The 20Amp GFCI will require a 20Amp beaker.

If your #6 is copper, then it has a rated ampacity of 75 which has to be derated by 80% to 60A. If it is aluminum, it has a rated ampacity of 55 which derates to 27.5 which you can round up to the next breaker size of 30A.


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RE: underground wiring

I have #6 copper to work with. The requirements for the barn are what ever capacity that wire will carry at 300ft. That's because I already have the wire stored from a few years back when a 250" roll of 14/2 with ground was $18.00!!! So I'll work with what I have. I can't even imagine what #6 copper RHW wire x 4 @ 300ft costs today. According to the above posting I can run 60amp at 300ft, so with 4 #6 conductors I would use a 2pole 60amp breaker at the main box. What if I dropped down to a 50 amp 220v circuit, what distance can I run then with this wire? Thanks


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RE: underground wiring

The ampacities have above have nothing to do with distance. It's the standard capacity for 90C wiring derated due to having more than three current carrying conductors in the conduit.

The amount of load you can run depends on how much voltage drop you can tolerate in the barn. Since it seems that the wire size is fixed, it doesn't seem like it matters. You still use a 60A breaker.

To compute the voltage drop you'll need the ACTUAL load drawn and the distance (and the #6) wire size. You can google to find several calculators that will let you know what kind of drop you're looking at.


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