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diy solar

Can I use thhn wire for ground/earth and bury it?

doox00

Solar Enthusiast
Joined
Jul 22, 2023
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301
Location
US-MI
Can I use thhn stranded copper wire for earth/ground and direct bury it? They bury bare copper wire when used as earth so I would think you could use it.. am I wrong?
 
It is not rated for direct burial.
I know that but it would only be used as earth/ground, they use bare copper and direct bury it when used as ground. Does anyone know for sure if it would fail an inspection?
 
I know that but it would only be used as earth/ground, they use bare copper and direct bury it when used as ground. Does anyone know for sure if it would fail an inspection?
It works just fine, doesn’t really matter what the insulation on a buried ground wire is. Only your AHJ would know for sure if it’ll pass inspection.
 
No, it would not pass an inspection.
Assuming that your inspector isn't completely useless. (Some are)
 
Curious. Could one run this in flexible outdoor rated conduit to the ground rods?
 
Curious. Could one run this in flexible outdoor rated conduit to the ground rods?
Yes (appropriately sized), which depends on if it's EGC or GEC.

This doesn't really come up much in DIY though. Since we don't really recommend supplemental ground rods, and people only bury new ground rods every time they make a new structure.
 
Weird, what’s the (electrical) reason for that?
Probably a physical damage reason.

I believe you need an explicit NEC exception to run bare EGC outside of a wiring method. There are such exemptions for under solar array and retrofit EGC for old circuits without ground.
 
Since we don't really recommend supplemental ground rods, and people only bury new ground rods every time they make a new structure.
Was thinking of when a ground is run to the main structure ground rods. Not supplemental. I know there are depth considerations for different conduits but was curious.
 
Not rated for direct burial.
But does it matter since it is just a ground/earth though? I am running PV wires from a solar array, using direct burial wire for the array, I wanted to use the thhn that is grounded to the array back to the solar shed where all the grounds run to and gets hooked to a grounding bar that the rest of the system grounds too.
 
Was thinking of when a ground is run to the main structure ground rods. Not supplemental. I know there are depth considerations for different conduits but was curious.
It depends on its purpose.
If it's an EGC, it's purpose is electrical safety, and must be protected from physical damage.
A GEC is usually very short, and less likely to be damaged. But even then, it should be protected if it is located in a place where it's likely to be damaged.
 
But does it matter since it is just a ground/earth though?
You are mixing terms.
The EGC for the solar array, has nothing to do with earth. Other than the fact that the earth is also connected to the grounding system.
The grounding system should only connect with earth at one location. This is usually at the same place as the N/G bond, but not always.
 
Okay, can I use my direct burial PV 10 gauge wire as ground then? It has red insulation, can I just mark it with green tape on each end?
 
Okay, can I use my direct burial PV 10 gauge wire as ground then? It has red insulation, can I just mark it with green tape on each end?
That would depend on its size. If smaller than #4 AWG, it can not be re identified as ground. If #4 or larger, it can.
 
My stamped engineered plans show 10 gauge grounds to each array.
Depending on what your inspector will be okay with, you might be able to get away with spray painting the ends completely green, where they can be seen.
My local inspectors would be fine with this. But yours may not.
 
Okay, can I use my direct burial PV 10 gauge wire as ground then? It has red insulation, can I just mark it with green tape on each end?

Not sure why you would have that much direct burial individual circuit (current carrying) conductors sitting around. I'd take a pause before buying stuff. I'm not sure direct bury individual PV conductors are recommended/allowed, over using 10/2 USE cable or something. By default I assume things need to be in a multi-conductor wiring method, unless someone gives me a code citation excusing running conductors separately. There probably is a PV direct burial exemption, since they sell it. But just because I see it in a catalog, doesn't mean I understand the conditions of use.

Also your wiring callouts (3) are mislabeled as low voltage 48V, it's probably carrying 300 VDC
 

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