Split 400A service grounding question (with Enphase)

[innavent]

Hello all,

I have a customer in San Diego County where we are splitting the system to back-feed one 200A sub-panel and one 200A section built into the 400A main. I've seen grounding done both ways:

1) separate EGC (from the GEC) connected to the inverters and modules run all the way to each 200A sub-panel, and

2) combine the EGC from the modules and inverters with the Enphase inverter ground GEC in the AC disconnect at the end of the engage cable string (and still run it to each 200A sub-panel). If option 2 is done, would you use an irreversible crimp (assuming your transition is from solid bare to solid THHN/THWN)?

I'm wondering if option 2 hasn't been an issue in the past because it's 'hidden' in the ac disconnect at the end of each inverter string? We have some contention about whether option 2 is allowable.

Second question is, we've run separate EGC in the past for each Enphase string then terminated them at the service panel vs. running a EGC through all modules and inverters in the system. As long as they all terminate in the same place, they do not need to be bonded together correct?

Thanks for your help in advance!

 

[jaggedben]

First of all happy thanksgiving.

I'll leave aside the issue of why you are splitting the up the system interconnection points, and assume you have a good reason for not putting it all into the 400A main. (It would certainly simplify your grounding if you could.)

As far as grounding, the guiding principles are more or less this:
-The GEC must go to the grounding electrode system, which usually means crimping to the existing AC GEC.
-EGCs must terminate in the same place where the branch circuit originates.

Given that, here's what I would suggest you do, based on the level of detail available.

1) Run a GEC to all inverters and bring it to your j-box or disco for the circuit conductors that are going to the main panel. Bond all the modules to the GEC as well. Combine this GEC with the Engage cable EGCs for the circuits that are interconnecting at the main, and run it back to the AC GEC, as in your 'option 2' method.
2) Run a separate EGC with the circuits that go to the sub. Only the Engage cable EGCs for those circuits are connected to this EGC.

If option 2 is done, would you use an irreversible crimp (assuming your transition is from solid bare to solid THHN/THWN)?

Yes, the irreversible crimp is required for the GEC or combined GEC/EGC. I hope your transitioning to stranded THWN not solid.

We have some contention about whether option 2 [combined GEC/EGC] is allowable.

The NEC explicitly allows this, so I'm not sure what the contention would be.

Second question is, we've run separate EGC in the past for each Enphase string then terminated them at the service panel vs. running a EGC through all modules and inverters in the system. As long as they all terminate in the same place, they do not need to be bonded together correct?

Assuming you mean GEC not EGC, that's an acceptable method. But it's a waste of wire if you can combine them all on the roof and run a single 8awg combined EGC/GEC to the service panel. In your case, you can do that for the circuits that go to the service panel, and run a separate EGC for the circuits that go to the subpanel.

 

[innavent]

Thank you so much! Happy Thanksgiving to you too. What you're telling me is basically what we'd thought (we are running THHN).

Have a great one!

Kevin