Grounding/Bonding as it pertains to overground cabling methods - Utility Scale PV installs.

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Ckennedy

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Hi All,

I've been poking around a while here and am intimidated by the wealth of knowledge. I'm posting only because I cannot find an answer I've been looking for so I need some help.

What are the grounding bonding requirements for a utility scale PV system when it comes to an over-ground cabling system like CAB other messenger wire based hangers? I'm based out of Canada but manage projects in the USA as well.

I'm an electrician here with a strong knowledge of the CEC and there is really nothing that dictates the need for grounding within the hangers. The system should be bonded at either end via termination points and the equipment should be bonded via the piles or grounding grid. Am I correct in assuming the same is true in the NEC?

Example:

Currently dealing with a system that requires 22 x 600mcm aluminum cables per hanger to be hung over-ground (landfiill, cant penetrate). Wondering if we need to run a separate ground within the CAB style hangers? I'm thinking we don't need it at all as the messenger wire is isolated from the cables and the cables will be terminated at each end into a box that's bonded to the grid.

Thoughts?
 
In general the NEC requires that an Equipment Grounding Conductor be installed with the circuit conductors. Not sure of any section in the NEC would permit an installation like you are describing.
 
don_resqcapt19 said:
In general the NEC requires that an Equipment Grounding Conductor be installed with the circuit conductors. Not sure of any section in the NEC would permit an installation like you are describing.
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As there's an existing grounding grid for the equipment and all of the equipment is already grounded, is this used as a backup system? Seems a bit redundant.

Also, the equipment is attached to piles that are 5-10ft into the ground, usually 14 gauge steel or 8' round steel pipe.... tied in with whips to the racking.

It's not a problem to run a ground in the hanger but I cant find anything in the NEC that directly explains if/why it is needed. Can you point me in the direction of that? I understand that this is probably considered a raceway type installation but not fully confident on that either...
 
A ground grid or other connection to earth does not take the place of an EGC. 250.112, the last part of the parent text requires most electrical equipment to be connected to an EGC.
That is not a raceway installation as you are not installing conductors in a raceway. It sounds like Messenger Supported Wiring, Article 396. The messenger can be used as the required EGC in some cases.
 
don_resqcapt19 said:
A ground grid or other connection to earth does not take the place of an EGC. 250.112, the last part of the parent text requires most electrical equipment to be connected to an EGC.
That is not a raceway installation as you are not installing conductors in a raceway. It sounds like Messenger Supported Wiring, Article 396. The messenger can be used as the required EGC in some cases.
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So then I'll just need to run a bare copper wire of appropriate size within the hanging system and run a jumper from the messenger wire to the EGC?

Sounds pretty easy.. almost too easy, hah.

Thanks for the help Don.
 
I agree with Don. The messenger is the EGC, and per the NEC it must be run with the circuit conductors. Not to mention that it's a bare metal part that must be bonded anyway.

It might be cliche to mention here, but grounding is not bonding. And note: The NEC doesn't require the grounding grid, but it does require an EGC run with the circuit conductors when the leave arrays. So if you're going to leave out something and still meet NEC requirements, it would be the grounding grid. You can ground each array separately as long as you have EGCs connecting them.

I don't think the grounding grid serves any purpose unless its for lightning protection, which is outside the code and would be a subject for an LPS expert.
 
jaggedben said:
I agree with Don. The messenger is the EGC, and per the NEC it must be run with the circuit conductors. Not to mention that it's a bare metal part that must be bonded anyway.

It might be cliche to mention here, but grounding is not bonding. And note: The NEC doesn't require the grounding grid, but it does require an EGC run with the circuit conductors when the leave arrays. So if you're going to leave out something and still meet NEC requirements, it would be the grounding grid. You can ground each array separately as long as you have EGCs connecting them.

I don't think the grounding grid serves any purpose unless its for lightning protection, which is outside the code and would be a subject for an LPS expert.
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There seems to be a lot of back and forth in the NEC. Not quite contradictory but definitely left up to a lot of subjective interpretation.

I'm just trying to see if I need an EGC within the hangers that are attached to a messenger cable. These hangers carry cables. The messenger cable is attached to the metal structure which is attached to a metal pile which is driven into the ground. The metal structures and the equipment on these structures are bonded to the structure which is obviously grounded by way of it being 10+feet into the ground using 80-200kg of steel.

Making my head melt that this isn't good enough and that I'd have to run a supplementary EGC within the hangers for the sole reason that they have cables in them... which are grounded at each termination point.....
 
Ckennedy said:
So then I'll just need to run a bare copper wire of appropriate size within the hanging system and run a jumper from the messenger wire to the EGC?

Sounds pretty easy.. almost too easy, hah.

Thanks for the help Don.
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You don't need an extra wire if the messenger is the EGC. Some of the pictures on the CAB website show a bare copper wire for the messenger. (Others seem to show an aluminum wire, also okay but obviously trickier to bond directly to copper jumpers.)
 
jaggedben said:
You don't need an extra wire if the messenger is the EGC. Some of the pictures on the CAB website show a bare copper wire for the messenger. (Others seem to show an aluminum wire, also okay but obviously trickier to bond directly to copper jumpers.)
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That other wire is a simple steel aircraft cable and I don't see an EGC within the hanging system which has me so confused. The copper wire is a steel wire that's cladded in copper, so I understand that part of it. It's the other pictures that have me confused.

As seen below....

Also, looking at it now.. even if the messenger wire was used as an EGC, is it not insolated due to the rubber/plastic coating?
 

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I'll have to admit to lacking experience with those particular wire types, although it seems to me that the insulation could be stripped where it's bonded to equipment.

BTW the steel in the ground may provide some reduction of shock hazard but is not reliable for triggering the ground fault detection on the inverter that would alert you to ground faults that could cause fires. (First ground fault doesn't cause a problem if not detected, second fault on the other side of the circuit closes an uncontrolled PV circuit and looks like a stick welder.) It's true that if you have a ground grid that it could perform the same function, but personally I don't like the idea of being unable to inspect the bonding after installation. And the NEC doesn't really allow it.
 
Only reason why I suspect it's steel wire is because AL would crumple under the weight of that. hah.

Just mystifying how common sense got missed on this it seems. The EGC in any version seems to be overly redundant in this type of install.
 
Ckennedy said:
. The EGC in any version seems to be overly redundant in this type of install.
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Maybe. Note that most of what you are doing is bonding. Connecting everything to dirt doesnt really do much, so it doesnt matter that you have a "structure which is obviously grounded by way of it being 10+feet into the ground using 80-200kg of steel."

Note that there is lots of silly stuff that goes on in PV systems and it can make things confusing. What I mean is there are often all sorts of grounding and bonding stuff that the designer puts in that doesnt serve any NEC purpose or even accomplish anything other than apparently making them sleep better at night. For example, I worked on a utility scale PV system that had this "bonding wire" that was routed around the array and attached to the combiner panels and inverters. It didnt meet any NEC requirement and caused some confusion as to what its purpose was.
 
don_resqcapt19 said:
In general the NEC requires that an Equipment Grounding Conductor be installed with the circuit conductors. Not sure of any section in the NEC would permit an installation like you are describing.
Click to expand...

I am shooting from the hip here without checking the wording, but i believe 690 only requires the EGC to be routed with the other conductors when it leaves the vicinity of the array. I am not sure if there is a consensus on whether different isolated rows of a ground mount array are the same array? IF they are, it would seem an isolated ground ring or bonding wire could be used as the EGC if it met the other NEC requirements as far as size and termination.
 
electrofelon said:
Can a steel messenger wire be an EGC? I dont see that listed in 250.118
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Maybe if it is listed? I'm curious about the claims on the CAB website. CEC, but not NEC? 250.118 doesn't say 'other listed EGCs'.

So yeah, barring that, I made incorrect assumptions about those pictures and if those messengers are not copper or aluminum conductos then you would need another EGC in the hangers.

Not entirely convinced that a copper or aluminum messenger wouldn't be strong enough, although I'm sure it depends on the details of what it's asked to hold up.
 
electrofelon said:
I am shooting from the hip here without checking the wording, but i believe 690 only requires the EGC to be routed with the other conductors when it leaves the vicinity of the array. I am not sure if there is a consensus on whether different isolated rows of a ground mount array are the same array? IF they are, it would seem an isolated ground ring or bonding wire could be used as the EGC if it met the other NEC requirements as far as size and termination.
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Not that I'm in charge, but I bet it's cost effective down the line from a service and troubleshooting standpoint to take the equivalent amount of copper out of the ground grid and put it into the hangers as EGCs. Like I said above, if I'm troubleshooting that system 15 years later I don't want to be guessing which rows of panels still have a good connection to the ground grid, or trying to find documentation that a ground grid was even installed to plan.
 
jaggedben said:
Maybe if it is listed? I'm curious about the claims on the CAB website. CEC, but not NEC? 250.118 doesn't say 'other listed EGCs'.

So yeah, barring that, I made incorrect assumptions about those pictures and if those messengers are not copper or aluminum conductos then you would need another EGC in the hangers.

Not entirely convinced that a copper or aluminum messenger wouldn't be strong enough, although I'm sure it depends on the details of what it's asked to hold up.
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Yeah not sure, I mean ACSR is used as an EGC most of the time, and I don't really even see that as meeting anything in 250.118. not sure if when they State the size of ACSR it's only the aluminum conductors? Or does that size include the steel strand?
 
jaggedben said:
Not that I'm in charge, but I bet it's cost effective down the line from a service and troubleshooting standpoint to take the equivalent amount of copper out of the ground grid and put it into the hangers as EGCs. Like I said above, if I'm troubleshooting that system 15 years later I don't want to be guessing which rows of panels still have a good connection to the ground grid, or trying to find documentation that a ground grid was even installed to plan.
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Yeah for sure, I would skip any sort of
separate, possibly superfluous, ground ring or inter-row bonding jumper and just route it with the conductors.

I wonder if the op could just use a piece of ACSR for the messenger? Even if it has to be large, probably cheaper than a separate EGC in the hangers.
 
Ckennedy said:
Example:

Currently dealing with a system that requires 22 x 600mcm aluminum cables per hanger to be hung over-ground (landfiill, cant penetrate). Wondering if we need to run a separate ground within the CAB style hangers? I'm thinking we don't need it at all as the messenger wire is isolated from the cables and the cables will be terminated at each end into a box that's bonded to the grid.
Click to expand...
A bit of a hijack of this discussion but I'm curious how you are doing the ground electrode system in capped landfills? Most of the time in the projects I see we can't disturb the soil deeper than 6" so have to go with a UFER electrode on the cap. Some clients don't want to use a UFER and that means putting in a grounding electrode system off the cap and running long grounding electrode conductors.
 
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