Grounding Chassis to AC Earth Ground

[RayWranglerMD]

Can the chassis ground on the Classic 250 be grounded to the earth grounding rod for the existing AC breaker panel which is independently powered by a generator only. Nothing on the solar side is grounded yet (not panel(s), nor batteries, nor metal chassis) and in reading the Midnight directions it appears the controller and batteries can both be grounded using the chassis ground lug on the classic down to the earth ground (rod) without changing any of the default GFP settings nor removing the internal Classic GFP jumper.

Would a fault on the separate AC generator powered system affect the separate DC solar components if the solar controller was connected to the AC system at a shared earth grounding rod?

Setting up a new off grid DC only system (no inverter, nor tie to existing 10kw generator powered AC circuits) with Classic 250, 12v battery bank, DC fuse block and simple 12v wiring circuits for lights, USB ports, and CPAP breathing machine.

[Vic]

Hello Ray,   Welcome to the Forum.

There can be a lot involved with grounding.   Personally I try to not give any advice,   as there are so many variables,   and  on a Forum,   we are using the eyes and information of others.

If you are in the USA,   the National Electrical Code (NEC)  is the primary guide for safe,   Code compliance.

The following should give a good overview:
https://www.mikeholt.com/instructor2/img/product/pdf/1292448885sample.pdf

Your system is not the customary system design that most of us here,   deal with.  The wiring diagrams for the Classic,   and MidNite E-Panels should show customary grounding for common system designs.

FWIW,   Good luck,   Vic

[boB]

In addition to Vic's advice, I would say that the ground point is at the AC source.

In you case, the source is the generator and it is running into that main breaker panel.  That panel is where the main ground to generator and AC distribution to the loads should be connected to the ground rod, typically.   

Then, the Classic's chassis ground lug can connect by way of a wire to that main breaker panel ground point.

The DC negative (typically) can also be grounded to that AC panel.

Do you have any lightning protection ?  SPDs ?   those too have a ground and would be for your solar PV+ and PV- lines if you do.

Sounds like you are probably good to go though.   


This next part is extra and you should not have to pay any attention to it but here goes....

What I do sometimes as a sanity check is to measure the potential voltage difference between two points before I connect them together if I fear anything bad.  AC and DC measurements.  Sometimes there is "leakage" and you might measure a voltage difference BUT there is not any real force behind it.  That's when I bring out a resistor and connect them between the two points if I'm afraid I'm going to get any sparks or smoke.  If it is leakage, then even with a fairly high value of resistance, that voltage might drop to zero or almost zero proving it was just some kind of small leakage.


OK, let us know how it goes.  You're probably just fine connecting things together I would think.

[RayWranglerMD]

Thank you very much for the great input(s). I have grounded the PV system to the shared earth ground rod (shared with 10kw AC generator grounds). I plan to add an SPD to the system which is hopefully as straightforward as I understand them to be. Thanks again, the knowledge base available in this forum is an excellent resource.

[ICPete]

The DC negative (typically) can also be grounded to that AC panel.

I'm designing a new multimode grid-tied and battery-backup PV system for my residence.
My understanding of the 2017 NEC (applicable to my location) is that PV source conductors on buildings must have GFP.
That would mean the DC negative of the Midnite Classic(s) would NOT want to be connected to the building ground (GEC).

Can you please clarify? I realize there are folks out there who entirely disagree with GFP for DC PV charging systems, but the code is the code.

I'll post my related question about the consequences of GFP in another topic.
But I'd like clarification if boB's quoted statement above applies ONLY IF you wish NOT to use the Classic's GFP.

Peter