PVC as conduit

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Old 09-27-18, 12:58 PM
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PVC as conduit

I was searching for conduit and came across a list of different types along with pros and cons for each. With the pvc it mentioned having to use a separate ground wire which I don't understand since the cable run thru the pvc conduit has a ground wire. I have used pvc schedule 40 before and didn't run a ground wire separate from the cable. What would be the purpose of a separate ground wire? I read this on Home Depots buying guide for conduit. If a separate ground wire is required what recourse do I have with the work I did several years ago using pvc?
 
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Old 09-27-18, 01:34 PM
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Normally individual conductors are used in conduit not cable. Individual conductors require a ground but cable doesn't.

Use note NM-b cannot be used in buried conduit .because it is a wet location.
 
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Old 09-27-18, 02:38 PM
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I have to run some 12/2 wire to the opposite side of my house by way of metal conduit buried in a trench. Using metal conduit saves me from digging 18 inches of hard soil to put in the UF alone. I'm allowed to bury it 6 inches if it is in metal conduit. I'm getting flexible metallic waterproof conduit. So, do I put in individual conductors plus ground in the conduit or should I fish 12/2 cable thru it?
 
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Old 09-27-18, 04:11 PM
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I'm getting flexible metallic waterproof conduit
Flexible metallic conduit cannot be used underground.
Also, not any kind of metal conduit can be used underground.
You need galvanized or stainless steel rigid metal conduit or inter mediate metal conduit. Regular EMT conduit will corrode away in few years.
Running rigid metal conduit won't be easy if you don't have right tools. They are pretty much galvanized pipe and you will need to cut thread on any cut sections.

You are better off digging deeper and run PVC conduit. You can rent a trencher to make things easier.
You only have to go 18". If you install GFCI breaker and the circuit is less than 20A, you can go 12".

So, do I put in individual conductors plus ground in the conduit or should I fish 12/2 cable thru it?
You can use both. But you cannot use NM-b.
Even if you put the cable in conduit, you have to use UF cable or use THWN wires.
 
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Old 09-27-18, 05:47 PM
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Is it the one otherwise known as liquid tight conduit?
 
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Old 09-27-18, 06:55 PM
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Liquid-Tight Flexible Metal Conduit (Seal-tite) is actually approved for direct burial. Of course it needs to be marked as such and would be the most expensive wiring method.
 
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Old 09-28-18, 10:02 AM
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Liquidtight also requires burial depth of 18", just like PVC. Only threaded rigid steel conduit is allowed at 6" depth.
 
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Old 09-28-18, 10:05 PM
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"If you install GFCI breaker and the circuit is less than 20A, you can go 12" My breakers are going to be 20amps. What's the relationship with the 12" and a breaker less than 20amps? I guess I will go with the PVC and just dig deeper. I don't think I'm up to working with the rigid metal.
 
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Old 09-28-18, 10:14 PM
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It can be 20A. It's 20A or less. The run just needs to be GFI protected.
 
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Old 09-29-18, 01:58 PM
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PJ, thanks. PVC at 12 inches with GFI breaker it is. Thanks to everyone who responded to my question. I had bought EMT and had wire pulled thru half. I guess I'll eventually learn not to begin a project until I have all the facts straight.
 
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Old 10-02-18, 12:32 PM
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I have two of three runs completed. I am short about 15 feet of cable and would like to know whether a junction box is allowed on the outside of house. Otherwise I'll have to buy 50 feet of new cable. Not a big deal as far as cost of overall project but would rather use what I have if possible.
 
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Old 10-02-18, 06:05 PM
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would like to know whether a junction box is allowed on the outside of house.
It is allowed using weather proof junction box. There are PVC junction box with cover that you can just glue PVC conduits right on to the fittings. It is also generally more watertight compared to metal junction box.

You are not allowed to bury the junction box though. It must remain accessible.

I would use gel filled water proof wire nuts if your junction box will be at the ground level.
 
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Old 10-02-18, 06:20 PM
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Does it have to be locked in any way?
 
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Old 10-02-18, 07:05 PM
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It does not need a lock. .
 
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