Underground 120V branch circuit installation for a residential sliding gate

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fandi

Senior Member
Location
Los Angeles
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Electrical Engineer
Hello,
There's a residential sliding gate that needs 120V power(not sure hard-wired or plugged-in). I read somewhere on this forum that because the THHN/THWN outer insluation will come apart and break down over time, only XHHW-2 wires can be used. Is that true? When the underground wires get up to the ground surface, it will not go straight to the house. Instead, the wires then connect to another 30ft run of Romex inside EMT conduit to get to the outdoor main electrical panel's breaker.
So my questions are:
- What types of underground wires can be used?
- The wires can be direct buried or they have to be in Electrical PVC conduit? (Either way the burial depth is 18" for a driveway of a single family house per table 300.5)
- If PVC is used underground, how does the PVC pipe couples with EMT conduit above ground? Can an outdoor j-box installed on the ground next to the outside wall? (The j-box sits on the ground will subject to water damage as that spot is the lowest spot in the area). Do they make pvc-emt coupler?
Thanks.

 
All the newer THHN is dual rated as THHN/THWN and is rated for outdoors, which is a wet location. You do have to put it in conduit. The NM (Romex) is not allowed outdoors in conduit.
Most of the XHHW-2 is rated for direct burial. However I usually put that in conduit as well due to the fact that it is easily damaged if hit by something or rocky ground that could nick it on backfill. Plus, if in conduit, it would be easier to replace in the future if needed.
So....THWN fine to use in conduit
XHHW-2 fine to use with or without conduit.
 
Either one can be used.

Both have to be in conduit, no direct burial.

Why are you using romex in EMT.

UF cable can be buried and used inside, no changeover needed.

A residential GFCI protected, 120V 20A circuit would have a burial depth of 12”.
 
Little Bill said:
All the newer THHN is dual rated as THHN/THWN and is rated for outdoors, which is a wet location. You do have to put it in conduit. The NM (Romex) is not allowed outdoors in conduit.
Most of the XHHW-2 is rated for direct burial. However I usually put that in conduit as well due to the fact that it is easily damaged if hit by something or rocky ground that could nick it on backfill. Plus, if in conduit, it would be easier to replace in the future if needed.
So....THWN fine to use in conduit
XHHW-2 fine to use with or without conduit.
Click to expand...
Thanks Bill for the quick reply. So THHN wires will be used 30' underground and 30' above aground. How do you couple the pvc and emt conduits? Thanks.
 
Little Bill said:
All the newer THHN is dual rated as THHN/THWN and is rated for outdoors, which is a wet location. You do have to put it in conduit. The NM (Romex) is not allowed outdoors in conduit.
Most of the XHHW-2 is rated for direct burial. However I usually put that in conduit as well due to the fact that it is easily damaged if hit by something or rocky ground that could nick it on backfill. Plus, if in conduit, it would be easier to replace in the future if needed.
So....THWN fine to use in conduit
XHHW-2 fine to use with or without conduit.
Click to expand...

Wanna explain burying XHHW and also the no conduit part?:blink:
 
In no particular order:

Being in conduit does not negate the need for W-rated wire.

If you use rigid conduit, the depth need only be 6".

I would use the same conduit type for the entire run.

Can you not bury the entire run to the panel?

As mentioned, GFIC protection reduces the depth to 12".

You could use UF at 18" and sleeve the stub-ups.
 
This thread was temporarily moved to an area accessible only to the moderators. In a PM exchange with the OP, I have learned that he is merely providing advice to a neighbor, and will not be involved in any electrical installation work. As this is therefore not a DIY situation, I am putting this thread back into the open forum. I apologize to the OP for the delay and inconvenience.
 
Last edited:
charlie b said:
This thread was temporarily moved to an area accessible only to the moderators. In a PM exchange with the OP, I have learned that he is merely providing advice to a neighbor, and will not be involved in any electrical installation work. As this is therefore not a DIY situation, I am putting this thread back into the open forum. I apologize to the OP for the delay and inconvenience.
Click to expand...

Thank you Charlie. This forum is one of the most beautiful things I have seen in my life. Also the tremendous work the mods have put in for free.
 
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