Ground conductor on a solar pole mount base

[DerrickM]

I am installing a pole mount system with an 8" sch 80 steel pipe buried in the ground approx. 8'.
The electrician I am working with has installed many street lighting poles and bases and recommended we install a ufer ground, attached it to the rebar structure deep in the concrete base and bring it up to the top of the base for future attachment.
Now microinverters no longer need a GEC, so the EGC in its cable is all you need in your branch circuit wiring and for bonding the circuit and the rails/ frames of your solar equipment.
I watched Mike Holts presentation on Auxilary grounding electrodes and how much he feels they add to the risk of lightning attacking your solar electronics etc. I'm thinking based on that, I do not want to connect that ground wire coming out of the earth to my microinverter branch circuit EGC because of this risk.
Why did we install the ground wire in the earth if we are not going to be using it or if it can cause serious damage from a possible lightning strike in the nearby earth?

Any thoughts?
Thanks,
Derrick

 

[jaggedben]

Thoughts, in no particular order...

- Even if you hadn't put in the UFERs, you'd probably still have the problem, because your poles themselves are only two feet short of NEC requirements for an electrode, and are thus likely to act as such anyway. Since you have wiring running between these metal poles it's probably wise to consider your bonding strategy between the structures regardless. If your poles were wood I might suggest that you not connect the UFERs to anything, but since you have steel in the ground then in my opinion your stuck with a risk you need to consider.

- How are you running your branch-circuit wiring to the poles? Underground? Or by chance overhead? I believe it could make a huge difference to the ultimate answers your question.

- Concerning lightning problems, the requirements or lack thereof for the micro-inverters are essentially irrelevant, and so is the wiring you run from the arrays to ground if that that isn't also a connection between the poles/UFERs. (i.e. if your not running wiring overhead). For example, with underground wiring you could run only an EGC, sized based upon the branch circuit breaker, from the array to ground level. But your bonding considerations between the electrodes still remain.

- The NEC really doesn't cover lightning protection, so if that is a serious concern in your area there's another code for that and you should consult a lightning protection expert. Some of the NEC's provisions may help mitigate lightning damage if the strike isn't too close, and other NEC provisions permit for (but don't require) installations that will make the situation much worse, as discussed in the video you viewed. Mike Holt's big objection to 690.47(D) in the 2014 NEC is that the code requires an electrode that is likely to make the situation worse but doesn't require the minimum bonding connections required elsewhere in the NEC to mitigate that danger. Namely, it doesn't require bonding jumpers sized to 250.66, because it's an auxiliary electrode. The electrode really shouldn't be required at all, and I believe it won't be in the 2017 code.

- The presumed danger here would be that lightning energy travels along a small grounding wire between your poles and their UFERs. In order to avoid that, I would probably size them at least to the minimum requirements for grounding electrode system bonding jumpers, which would be at least a #8 wire by table 250.66, or else consult a lightning expert with experience in the area.

 

[zman990]

I was always under impression that by grounding close to the pole mounted array will route any lighting strike directly to earth at it least path of resistance so since you would have one away from the house it wouldn't ever have ability to send surges to the loads at home.
Thus adding extra protection for the customer and there home but it is definitely not needed.


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[iwire]

I was always under impression that by grounding close to the pole mounted array will route any lighting strike directly to earth at it least path of resistance so since you would have one away from the house it wouldn't ever have ability to send surges to the loads at home.

Electricity does not take the path of least resistance exclusively, it takes all available paths.

So while the remote electrode will likely divert some of the surge it will not prevent the surge from heading towards the home as well.

 

[jaggedben]

I was always under impression that by grounding close to the pole mounted array will route any lighting strike directly to earth at it least path of resistance so since you would have one away from the house it wouldn't ever have ability to send surges to the loads at home.
Thus adding extra protection for the customer and there home but it is definitely not needed.

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Let's be clear, if a lightning bolt directly strikes the array on the pole everything will be destroyed, so that's not what this is about. If you want to protect property from direct strikes there's another code for that (NFPA 780) and it involves a whole lot more.

What's at stake here is voltage gradients from lightning strikes that are not direct but may be nearby enough to do damage. This video from our host here isn't short, but it explains the whole issue and it really changed how I look at a lot of these grounding questions.

I think there may be something to the notion that if you ground the array at its location then that can reduce the likelihood of the array being struck directly, but these other issues still come into play. I am also not a lightning expert beyond having watched that video.

 

[zman990]

Ya idk either I would just use egc it is ungrounded array 250.122 only one ground is needed

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