When Are Ground Rods Required at a Generator?

[jar546]

I've only seen a handful of installations that required this. As a matter of fact, I can probably count them on one hand. There are situations where ground rods are required at a generator. Who knows the answer as to under what circumstances ground rods are required at a generator?

 

[Mr. Inspector]

When the plans require them.

 

[jar546]

When the plans require them.

That is not the answer we are looking for. We are looking for an NEC-driven answer that not only changes the ground rod requirements, but how the system is wired and disconnected.

 

[steveray]

When it is a separately derived system

 

[wwhitney]

When it is a separately derived system

Does not require ground rods at the generator, merely requires a GEC (Grounding Electrode Conductor) to a GES (Grounding Electrode System). The adjacent building's GES could be used. In fact if the generator is sufficiently close to the structure, any ground rods you install for it must be connected back to the building's GES.

The only requirement I can see for a ground rod at the generator itself would be 110.3(B), if the listing standard requires one. Of course, until the 2020 NEC generators weren't required to be listed.

Cheers, Wayne

 

[steveray]

Does not require ground rods at the generator, merely requires a GEC (Grounding Electrode Conductor) to a GES (Grounding Electrode System). The adjacent building's GES could be used. In fact if the generator is sufficiently close to the structure, any ground rods you install for it must be connected back to the building's GES.

The only requirement I can see for a ground rod at the generator itself would be 110.3(B), if the listing standard requires one. Of course, until the 2020 NEC generators weren't required to be listed.

Cheers, Wayne

And what is that sufficiently close dimension in the NEC again?....Yes, they could use some other grounding electrode, such as rebar in the concrete supports, but my point was that it did not need it's own GES unless it was an SDS....But even that answer could be a little fluid...

 

[jar546]

Does not require ground rods at the generator, merely requires a GEC (Grounding Electrode Conductor) to a GES (Grounding Electrode System). The adjacent building's GES could be used. In fact if the generator is sufficiently close to the structure, any ground rods you install for it must be connected back to the building's GES.

The only requirement I can see for a ground rod at the generator itself would be 110.3(B), if the listing standard requires one. Of course, until the 2020 NEC generators weren't required to be listed.

Cheers, Wayne

I started this thread to educate, not debate technicalities. Far too often, I’ve seen inspectors call for ground rods at generators without understanding why. Many don’t know what a separately derived system actually is, let alone when it applies. Most residential inspectors may go their whole career without seeing one. And yet, they’re out there calling for ground rods by default, even when the generator doesn't require it. Meanwhile, they’re missing the bigger issue, like a neutral-to-ground bond in a non-SDS installation, which I’ve personally found on follow-up inspections.

The reason this matters is that education doesn’t come from just quoting code; anyone can open the book. It comes from understanding how the system works and knowing what to look for. A generator with a 4-pole ATS is a clue. A switched neutral is a clue. The bond location inside the generator is a clue. But none of that gets caught if the inspector doesn’t know what they’re looking at.

Your reply was technically accurate and appreciated, but I’d really like to see you start more discussions, too. You’ve clearly got the knowledge, and I think the forum would benefit even more if you shared your perspective from the top down now and then—help us all look at these issues in a broader context. It's easy to break something down once someone else posts it, but there’s real value in being the one who puts it out there in the first place.