Can my off grid panel share a ground rod with Grid tie panel

[Chris30559]

Hi Everyone,

I've tried to read through tons of threads looking for a similar situation as mine and came up empty. Sorry if it's been answered already. I also made a quick sketch of what I believe I should do but hope someone can double check. To me it seems ok.

So I have a XW6048 LF inverter powering an off grid panel, this panel is N-G bonded. This panel then feeds a sub panel maybe 20-30ft away, not terribly far, which feeds more off grid loads. This sub panel is right next to my grid connected main panel. My question is, can I connect the ground from my off grid sub panel to my main service panel, which is N-G bonded as well, but furthermore has the ground rod attached. Currently there are no other ground rods in the system. The main point of connecting the grounds to me is to get a ground rod connected to the off grid panels in some way. Its also my understanding all grounds can and should be connected together to a single ground rod.

Further lets assume at this point the grid mains "L1, L2, N" will never be connected to the inverter in any way. So, the 2 different N-G bonds should be OK right? since electrically they really have nothing to do with each other except for the common ground.


Thanks for any insight.
Chris

 

[Daddy Tanuki]

if L1, L2 and neutral are never connected then you are fine and dandy they are simply sharing a rod jammed into the earth and nothing else. I do not know about your inverter, but my magnum unbonds the neutral and ground whenever generator or grid power is present on its inputs there by eliminating any concerns. sounds like you could setup an ATS that you can wire up so that the inverter is the primary for those areas you currently have it set to an use the grid as backup for them.... just a thought

 

[Chris30559]

if L1, L2 and neutral are never connected then you are fine and dandy they are simply sharing a rod jammed into the earth and nothing else.

Thanks for your input, that is what I thought as well.

I do not know about your inverter, but my magnum unbonds the neutral and ground whenever generator or grid power is present on its inputs there by eliminating any concerns. sounds like you could setup an ATS that you can wire up so that the inverter is the primary for those areas you currently have it set to an use the grid as backup for them.... just a thought

Very good thought, I actually plan on doing exactly that, however my inverter does not make or break any bonds with neutral and ground, it is all done in the circuit breaker panel. However I do plan on adding a contractor to break my off grid N-G bond in the event I need to power my loads with the grid in which the L1,L2,N will all be on a contractor as well.. I will use the Low battery aux on the inverter to activate a contractor to connect grid power and likewise activate the off grid N-G bond contractor to disconnect.

 

[zanydroid]

What about getting rid of N-G relay and neutral switching. In this case you would have a single N-G bond in the main.

N-G relay is more for mobile applications where you will disconnect completely from shore

 

[Chris30559]

Interesting idea, so you're saying I should connect the neutral from the output of the inverter and the grid neutral permanently. Then my N-G Bond would be in the grid panel like you said. At which point I would only switch L1 and L2 from grid in the rare case I need "shore power" to my loads.

I do know my inverter N terminals for each output and AC input are internally connected already.

I don't want to leave L1 and L2 connected unless they are needed. Mainly because the inverter handles that poorly. I.e. tries to either load shave, charge, or passthrough.

 

[zanydroid]

Yes, then you can use a two-pole transfer switch, which might be easier to find. And you have one less thing that can fail / be misconfigured (Neutral-Ground relay)

You might be able to find some pros/cons on the forum if you look for comparison of two-pole vs three-pole transfer switch.

 

[Chris30559]

Yes, then you can use a two-pole transfer switch, which might be easier to find. And you have one less thing that can fail / be misconfigured (Neutral-Ground relay)

You might be able to find some pros/cons on the forum if you look for comparison of two-pole vs three-pole transfer switch.

I actually already have a 3 pole contactor that I'd use as the transfer switch, so that wouldn't have been the issue. But I do like the simplicity of what you describe. No N-G relay.

So there is no possible way the inverter L1 ,L2 could somehow use the N from the grid as a return right. I don't see how but just wanted to pose the question in case I was missing something.

 

[zanydroid]

So there is no possible way the inverter L1 ,L2 could somehow use the N from the grid as a return right. I don't see how but just wanted to pose the question in case I was missing something.

No it can’t.

If you want to read up on it I believe you are allowed to choose bond isolation transformer secondaries to grid neutral, which is a similar situation. in that case it would not have enough isolation to be considered a separately derived system under code and be subject to different rules than a SDS. I don’t know off hand what the consequences are.

As long as you don’t bond N-G again the bonded N should be ok.

The N and G should be sized large enough to carry fault current for most sane designs.