Grounding a stand alone sub panel

[timselectric]

I'm in a similar situation as OP and could also benefit from clarification (I'm shining the timselectric bat signal).

I have an off grid system with a Victron Multiplus II 48/3000 inverter with the AC out back feeding 120v into a sub panel (6 spaces, 12 circuits). I have a small 2600W floating neutral generator that I plan to connect to the inverter. The default behavior of the Multiplus is to disable its own N/G bond when the AC supply is connected (in my case, I start up the generator).

I'm thinking that it would be just as well to fully disable the N/G bond on the Multiplus and put the N/G bond in the sub panel (read: main panel), then connect the sub panel directly to my DC grounding bus bar (which is connected to the EGC).

This saves me from using a N/G plug on the generator, and I think should also allow me to avoid having to bond the generator frame to the ground system. Does this make sense?

Yes, that's exactly how I would do it.

 

[glandpuck]

It would seem that PV- is connected to ground, somewhere.
I would separate PV- connections and test in both directions for continuity with ground to determine where.

I found my problem. After carefully trouble shooting everything above ground that I could see and measure, I next had to look at the splice cans the master electrician installed in the ground. All of his splice bolts were wrapped in the insulating tape and then wrapped in electrical tape. But these are not really meant for wet locations. Plus over time the wires sticking out of the splice bolt pierced the covering tapes. And the material itself degraded and corroded ruining the splice. The PV+ to was the worse. The ground splices were not affected, The PV- to a lesser degree.
The attached photos speak for themselves.
The solution was to replace all of the splices with NSI EPDM rubber coated wire connectors designed for damp/wet and even submersible locations. This solved al of my fault issues and crazy codes. Plus, while the bad connection passed voltage through to the inverter, they were not passing amperage. Now my system is humming along like a happy toddler!

Installers really need to pay attention to indoor/outdoor/damp/wet/insulated/submerged, etc when it comes to making connections that will last and can be serviced and repaired.

 

[timselectric]

Glad that you figured it out.

 

[Nan_wpg]

I'm in a similar situation as OP and could also benefit from clarification (I'm shining the timselectric bat signal).

I have an off grid system with a Victron Multiplus II 48/3000 inverter with the AC out back feeding 120v into a sub panel (6 spaces, 12 circuits). I have a small 2600W floating neutral generator that I plan to connect to the inverter. The default behavior of the Multiplus is to disable its own N/G bond when the AC supply is connected (in my case, I start up the generator).

I'm thinking that it would be just as well to fully disable the N/G bond on the Multiplus and put the N/G bond in the sub panel (read: main panel), then connect the sub panel directly to my DC grounding bus bar (which is connected to the EGC).

This saves me from using a N/G plug on the generator, and I think should also allow me to avoid having to bond the generator frame to the ground system. Does this make sense?

We have almost the same setup. (I have a smaller panel and only one,circuit .) I think if you disable the ground relay AND run ground from your panel to the ground bus will you not have a ground loop? Your panel ground already runs to the multiplus, and then from multi to the ground bus.

I’m,still not clear when you disable the multi plus ground relay if it just turns off the relay only (and still leaves neutral bonded) or does it disable the N/G bond completely?

Here’s my set up (grounding not done yet):

 

[offgrid-curious]

I’m,still not clear when you disable the multi plus ground relay if it just turns off the relay only (and still leaves neutral bonded) or does it disable the N/G bond completely?

As I understand it, it will disable the N/G bond completely. Otherwise, the relay will disable the N/G bond when the AC input is active. I haven't actually done this yet, so can't speak authoritatively. My system is currently so over provisioned I don't even think I need a generator.

 

[Nan_wpg]

As I understand it, it will disable the N/G bond completely. Otherwise, the relay will disable the N/G bond when the AC input is active. I haven't actually done this yet, so can't speak authoritatively. My system is currently so over provisioned I don't even think I need a generator.

I would think it disables it completely. My multipluss has the N/G bond but I now have a panel so I think I will N/G bond at the panel.

Do you happen to have a picture or wire diagram of your system? Wondering why you’d run a ground conductor from your panel to the bus, if,you already run a 3 wire from the multi to your panel. Your multi has a ground connection to,the bus as well?

 

[offgrid-curious]

Unfortunately I don't have an updated diagram handy. I'll try to explain in words.

I have 3 ground bus bars across my system:

1. Outside in my MNPV6 combiner box. PV is bonded here and this bus bar is connected to a grounding plate.
2. My DC panel ground bus bar is bonded to the outside ground bus via PV Teck 90 cable.
3. The sub panel bus bar is bonded to the DC panel ground bus bar via the Multiplus AC Out 1 (the sub panel is connected to AC Out 1).

The Multiplus ground is connected to the DC panel ground bus bar.

I was planning on connecting my generator to the Multiplus AC In 1. The generator has a floating neutral. By disabling the N/G bond relay on the Multiplus and doing the N/G bond on the sub panel, I can always have the N/G bond on the sub panel regardless of whether the generator is running or not.

Does that make sense?