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Old 05-20-2011, 08:51 PM   #1
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Underground wire to lamp post


Hi all!

Looking to run conduit for a future outdoor brick pillar which will have a lamp on top. This is a new construction so the rough grade is currently about 6 inches below what the final grade will be and I want to get this installed before the landscapers come with the top soil.

The electricians ran the wiring through the basement to the point where it will exit the house and go to the post and I am planning on doing the rest.

I did some searching online and found several different opinions on what to use for conduit. Does PVC have to be buried deeper than rigid metal conduit, and is standard rigid metal conduit suited for underground use?

I guess the question is, what should I use for conduit and how deep? The less digging I have to do the happier I am

Thanks

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Old 05-20-2011, 09:10 PM   #2
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Underground wire to lamp post


18" deep. I would use the PVC. No worries about rusting out in future.

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Old 05-20-2011, 09:46 PM   #3
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Underground wire to lamp post


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Hi all!

Looking to run conduit for a future outdoor brick pillar which will have a lamp on top. This is a new construction so the rough grade is currently about 6 inches below what the final grade will be and I want to get this installed before the landscapers come with the top soil.

The electricians ran the wiring through the basement to the point where it will exit the house and go to the post and I am planning on doing the rest.

I did some searching online and found several different opinions on what to use for conduit. Does PVC have to be buried deeper than rigid metal conduit, and is standard rigid metal conduit suited for underground use?

I guess the question is, what should I use for conduit and how deep? The less digging I have to do the happier I am

Thanks
PVC, Schd 40 below, Schd 80 above or Schd 80 for both.

RMC is expensive and will rust out in 40 years, I think you can get it in AL, then it wouldn't rust. PVC is cheap, even schd 80 isn't that expensive and it never rusts, rots, etc.

No reason I can think of not to use PVC for anything underground residential.
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Old 05-20-2011, 10:01 PM   #4
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Underground wire to lamp post


if protected by a GFI UF cable could be only 12"
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Old 05-20-2011, 10:04 PM   #5
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I'd put it on a GFCI, and run 3x THWN wires in PVC conduit 12" deep. That's what I did for my lamp post.
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Old 05-20-2011, 10:06 PM   #6
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I'd put it on a GFCI, and run 3x THWN wires in PVC conduit 12" deep. That's what I did for my lamp post.
Ditto - this is what I did to a fountain.
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Old 05-20-2011, 10:37 PM   #7
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PVC sounds like the way to go.

I hope it's already on a GFCI breaker. The electricians installed a switch by the front door that feeds the wire in the basement that will eventually go to the light. There are 3 GFCI breakers in the main panel so I will have to test the wires to see if they are on one of those 3 circuits.

Thanks for your help
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Old 05-20-2011, 10:39 PM   #8
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Underground wire to lamp post


All you have to do is install a GFCI outlet on that line before it leaves the basement. Connect the light to the LOAD side of the GFCI outlet, then you are protected. Much cheaper than a GFCI breaker.
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Old 05-20-2011, 10:49 PM   #9
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Much cheaper than a GFCI breaker.
Definitely, and I actually have an extra GFCI receptacle laying around in a drawer that I can put to perfect use so it won't cost anything. Thanks for the tip!
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Old 05-21-2011, 07:36 PM   #10
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One more quick question... I have a length of 16/3 SOW cable that I bought years ago and I seem to recall being told that it was rated for contact with water, oil, etc. Is this wire up to code to use in underground conduit?

Thanks
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Old 05-21-2011, 07:51 PM   #11
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One more quick question... I have a length of 16/3 SOW cable that I bought years ago and I seem to recall being told that it was rated for contact with water, oil, etc. Is this wire up to code to use in underground conduit?

Thanks
No, not rated for use in conduit - it's used more like in a power cord senario.
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Old 05-22-2011, 09:45 AM   #12
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2 problems with your suggestion of using 16/3 SOW cord...(1) 16 gauge is less than the minimum required size of wire for any branch circuit wiring in a house (2) Cords cannot be used in place of a building fixed wiring system.
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Old 05-22-2011, 11:00 AM   #13
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OK, thanks for letting me know.
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Old 05-28-2011, 12:35 PM   #14
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Underground wire to lamp post


OK I picked up the PVC and I got one of these:



I will have to drill a hole in the foundation of the house to pass the PVC pipe through.



Where you see the gray below the siding, there is wood behind the plastic cover. There is actually a hole the foundation where a faucet was going to be but then it was moved due to that area being covered in soil. I am planning on using the existing hole for the PVC.

When I've seen one of the above PVC connectors on a house, it's always above ground. This will eventually end up being covered in dirt when the landscaping is done.

2 questions arise: Is this the wrong type of PVC connector for being below ground, and although this isn't exactly an electrical question, is standard exterior caulk going to be sufficient to keep moisture from seeping in where the PVC enters the building below ground?

Also, the home center had a specific type of cement for this PVC. I already have PVC primer and cement used for standard plumbing pipe. Is the glue I have not compatible with PVC conduit?

Any input is appreciated
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Old 05-28-2011, 01:59 PM   #15
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your glue is fine. this is not acceptable for underground, as it has to be accessible. If underground you need a 90. i would not use standard caulking

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