Use of bare copper conductors for grounding PV modules

[philly]

I'm looking at a design that calls for bare copper ground conducotrs to be used for grounding the various PV modules/structures in an array. I was wondering however if there was anything in the NEC that required these conductors to be bare, or if they could be THHN conducotrs with a jacket? I do not believe there is anything preventing the use of THHN cables other than it will be easier to terminate the bare copper condutors to the modules since you dont have to strip the cable to land it on grounding lugs.

For all the ground cables from the combiner boxes to the inverter, etc.. regular THHN cable is called for the ground? Is there anything in the NEC that dictates what type of cable bare conductor or otherwise is to be used for PV installations?

 

[ggunn]

I'm looking at a design that calls for bare copper ground conducotrs to be used for grounding the various PV modules/structures in an array. I was wondering however if there was anything in the NEC that required these conductors to be bare, or if they could be THHN conducotrs with a jacket? I do not believe there is anything preventing the use of THHN cables other than it will be easier to terminate the bare copper condutors to the modules since you dont have to strip the cable to land it on grounding lugs.

For all the ground cables from the combiner boxes to the inverter, etc.. regular THHN cable is called for the ground? Is there anything in the NEC that dictates what type of cable bare conductor or otherwise is to be used for PV installations?

Are the grounding lugs for the modules listed for stranded wire?

 

[philly]

Are the grounding lugs for the modules listed for stranded wire?

I'm not sure. They are the typical Brundy J-Lug type

 

[iwire]

I'm looking at a design that calls for bare copper ground conducotrs to be used for grounding the various PV modules/structures in an array. I was wondering however if there was anything in the NEC that required these conductors to be bare, or if they could be THHN conducotrs with a jacket? I do not believe there is anything preventing the use of THHN cables other than it will be easier to terminate the bare copper condutors to the modules since you dont have to strip the cable to land it on grounding lugs.

For all the ground cables from the combiner boxes to the inverter, etc.. regular THHN cable is called for the ground? Is there anything in the NEC that dictates what type of cable bare conductor or otherwise is to be used for PV installations?

The NEC allows insulated or bare EGCs.

However if the design calls for bare why would you use anything else?

 

[philly]

The NEC allows insulated or bare EGCs.

However if the design calls for bare why would you use anything else?

I am the one behind the design and have the contractor asking if he can use either.

I specified bare because I thought it would be easier to terminte on module lugs.

I want to give contractor the option of using either, but want to make sure there are no code issues with using either.

So are you esentially saying that ground conductors weather they are ECG, GEC's, etc.. can be either bare or stranded (THHN)? If they want to use stranded for grounding the modules I do not see an issue with this, I just want to make sure this is not violating any code issues?

 

[ggunn]

I am the one behind the design and have the contractor asking if he can use either.

I specified bare because I thought it would be easier to terminte on module lugs.

I want to give contractor the option of using either, but want to make sure there are no code issues with using either.

So are you esentially saying that ground conductors weather they are ECG, GEC's, etc.. can be either bare or stranded (THHN)? If they want to use stranded for grounding the modules I do not see an issue with this, I just want to make sure this is not violating any code issues?

I don't think you can use THHN where the wiring is outdoors and exposed, but either way I'll wager that the installer would prefer to use solid bare copper. Having to strip insulation at every lug would be a pain.

 

[philly]

I don't think you can use THHN where the wiring is outdoors and exposed, but either way I'll wager that the installer would prefer to use solid bare copper. Having to strip insulation at every lug would be a pain.

This is what I would have thought, that the contractor would not want to strib the stranded cable at every lug but he is the one who is asking?

So are you saying that you cant use standed cable where not protected in a raceway such as conduit? I have seen many installation where a stranded ECG was run ouside of a raceway? Any NEC requirment?

One of the construction managers is saying that he doesn't think bare copper conductors can be run in conduit? Any truth to this in the NEC? The only thing I recall in the NEC related to this is that I believe a bare grounding electrode conductor (GEC) can't be run in conduit due to a choke effect? Does anyone know of any section prohibiting the use of bare copper in conduit?

 

[jaggedben]

I wouldn't use stranded wire THHN wire for an exposed EGC on a PV array, because I wouldn't trust it to be as mechanically durable if the insulation decays in the sun and comes off. That said, I don't know where in the NEC it is clearly prohibited to use stranded wire.

If it is okay to use a bare solid conductor for an EGC, then it stands to reason that it is okay to use an insulated solid conductor (THHN or otherwise), because the insulation is superfluous to the purpose and it does not matter if it decays. Perhaps the contractor can find insulated wire at a cheaper price because there is more supply, and is willing to strip insulation because he thinks he will still save money. I would say that is his prerogative, as long as it solid wire.

I have both heard and know from experience that it is often a stupid idea to run larger solid conductors inside conduit, bare or otherwise. I would tell you not to run a bare #8 ground inside 3/4" conduit because your wire pull will turn a good day into a bad one. But it doesn't violate the NEC AFAIK.

 

[ggunn]

So are you saying that you cant use stranded cable where not protected in a raceway such as conduit?

No, I am saying that I don't think THHN can be run outside of conduit outdoors whether it is stranded or solid. You could run USE-2 as an insulated EGC, I guess, but it would be very expensive and a real pain to work with. Bare copper is the industry standard for this application for a reason; it's easy to work with and cheaper than insulated wire of the same gauge. I don't see why they would want to use anything else. Has your contractor ever done solar before?

You can get bare stranded copper, you know, but I've never seen it used as a solar module EGC; you'd have to confirm that the lugs are listed for it. Also, your AHJ may have something to say about this.

 

[ggunn]

If it is okay to use a bare solid conductor for an EGC, then it stands to reason that it is okay to use an insulated solid conductor (THHN or otherwise), because the insulation is superfluous to the purpose and it does not matter if it decays.

There you go using logic to predict what the NEC would say.

 

[philly]

No, I am saying that I don't think THHN can be run outside of conduit outdoors whether it is stranded or solid. You could run USE-2 as an insulated EGC, I guess, but it would be very expensive and a real pain to work with. Bare copper is the industry standard for this application for a reason; it's easy to work with and cheaper than insulated wire of the same gauge. I don't see why they would want to use anything else. Has your contractor ever done solar before?

You can get bare stranded copper, you know, but I've never seen it used as a solar module EGC; you'd have to confirm that the lugs are listed for it. Also, your AHJ may have something to say about this.

Just so I am correct on the terminology.

Bare copper conductors (lets say #6) are typically a solid conductor correct? But it sounds like you are also saying you can buy a bare copper stranded conductor for the same purpose as long as equipment is UL listed? Typically though bare copper is solid.

Insulated cable is stranded. Even though it is stranded it can still be used as an ECG and does not violate the NEC, it would just be more difficult to use.

So in summary:

1) For an EGC Bare solid or stranded can be used
2) For an EGC Insullated stranded can be used (has to be rated for outdoor exposure)
3) Either bare/stranded, insulated/non-insulated can be run inside conduit?

Is this correct

 

[ggunn]

Just so I am correct on the terminology.

Bare copper conductors (lets say #6) are typically a solid conductor correct? But it sounds like you are also saying you can buy a bare copper stranded conductor for the same purpose as long as equipment is UL listed? Typically though bare copper is solid.

Insulated cable is stranded. Even though it is stranded it can still be used as an ECG and does not violate the NEC, it would just be more difficult to use.

So in summary:

1) For an EGC Bare solid or stranded can be used
2) For an EGC Insullated stranded can be used (has to be rated for outdoor exposure)
3) Either bare/stranded, insulated/non-insulated can be run inside conduit?

Is this correct

Yes, you can buy stranded bare copper. Whether it is suitable for EGC, as allowed by code and your AHJ, I do not know. And yes, typically bare copper is solid.

Insulated conductors may be solid (up to AWG #8) or stranded.

1) I do not know if stranded bare copper can be used as EGC.
2) Insulated conductors can be used for EGC in general. I do not know for sure that if insulated the insulation must be outdoor rated if used for module EGC, but my guess would be that it does.
3) I'm pretty sure that bare copper can be run in conduit, but usually we transition it to stranded and insulated wire for conduit runs.

The way we usually do this is to run the PV home run wiring in USE-2 and the EGC in solid bare copper from the array to a combiner/transition/junction box, where the output wires are all THHN/THWN-2 in conduit. Also, individual AHJ's are sometimes specific about what is and is not acceptable for PV array ECG conductors. Check with them.

 

[jaggedben]

There you go using logic to predict what the NEC would say.

No way, I would never do that. Notice I didn't mention the NEC.

 

[jmellc]

I wouldn't use stranded wire THHN wire for an exposed EGC on a PV array, because I wouldn't trust it to be as mechanically durable if the insulation decays in the sun and comes off. That said, I don't know where in the NEC it is clearly prohibited to use stranded wire.

If it is okay to use a bare solid conductor for an EGC, then it stands to reason that it is okay to use an insulated solid conductor (THHN or otherwise), because the insulation is superfluous to the purpose and it does not matter if it decays. Perhaps the contractor can find insulated wire at a cheaper price because there is more supply, and is willing to strip insulation because he thinks he will still save money. I would say that is his prerogative, as long as it solid wire.

I have both heard and know from experience that it is often a stupid idea to run larger solid conductors inside conduit, bare or otherwise. I would tell you not to run a bare #8 ground inside 3/4" conduit because your wire pull will turn a good day into a bad one. But it doesn't violate the NEC AFAIK.

I don't have my book handy, but NEC prohibits solid wire larger than #10 from being pulled in a racceway. A single ground in a raceway may be an exception, not sure.

 

[cadpoint]

I thought the THHN qualifed something as being covered!

 

[T.M.Haja Sahib]

Using bare copper wire underground poses two prudent questions.
1)If there is sulphur in the soil,is the copper wire tinned?
2)Is the soil resistivity adequate enough to prevent electrolytic corrosion of buried building steel by the copper wire?

 

[jmellc]

Using bare copper wire underground poses two prudent questions.
1)If there is sulphur in the soil,is the copper wire tinned?
2)Is the soil resistivity adequate enough to prevent electrolytic corrosion of buried building steel by the copper wire?

Good questions. I never had the issue come up. I have buried hundreds of ground wires & never had a question on it. In the 70's, we more often left a few inches up & left clamp exposed.

 

[roger]

If all bare copper had to be solid, I'd hate to have to install lightning protection systems everyday using say 4/0 solid.

Roger

 

[ggunn]

If all bare copper had to be solid, I'd hate to have to install lightning protection systems everyday using say 4/0 solid.

But you do. It's called a ground rod.

 

[iwire]

Using bare copper wire underground poses two prudent questions.
1)If there is sulphur in the soil,is the copper wire tinned?
2)Is the soil resistivity adequate enough to prevent electrolytic corrosion of buried building steel by the copper wire?

Good questions. I never had the issue come up. I have buried hundreds of ground wires & never had a question on it. In the 70's, we more often left a few inches up & left clamp exposed.

Consider direct bury copper water lines last many decades

Consider a ground ring is a direct buried copper conductor.

I think T.M. is worrying about nothing.