Supplemental ground rod question

[KD4UPL]

I have a shop building with a 400 amp 240/120v service. There are 2 200 amp service disconnects on the shop. One feeds the shop, the second will feed a house on the same property. I'm running a 200 amp 4 wire feeder from this second service underground to supply the house about 250 feet away. About halfway between the two buildings I'm going to bring the feeder out of the ground to a mobile home panel mounted to pressure treated posts set in the ground. This panel will have an outlet to power my motor home when it's parked there, some outdoor lighting, and an electric wood splitter.

I don't think the NEC requires a grounding electrode at this remote panel. I will have a grounding electrode system at both buildings. My questions are:
I'm I correct that the remote panel doesn't need a grounding electrode?
Would installing a grounding electrode be beneficial?
Would installing a grounding electrode actually be a bad idea?

Thanks,

 

[LarryFine]

I'm I correct that the remote panel doesn't need a grounding electrode?

No, it needs an electrode.

Would installing a grounding electrode be beneficial?

Technically, no, but NEC requires it.

Would installing a grounding electrode actually be a bad idea?

No.

 

[KD4UPL]

Okay. Help me out. What is the code reference that says it needs a rod? We're under the 2014 NEC here by the way. I looked in 230, 250, and even 551 and couldn't really find anything saying it needed one.

 

[LarryFine]

It qualifies as a structure.

 

[roger]

Okay. Help me out. What is the code reference that says it needs a rod? We're under the 2014 NEC here by the way. I looked in 230, 250, and even 551 and couldn't really find anything saying it needed one.

250.30 or 32, I'm not in front of a code book at the moment.

Roger

 

[KD4UPL]

If it's a structure then I see how it would need one. I didn't think a breaker panel screwed to a post was a structure.
Thanks for the help.

 

[electrofelon]

If it's a structure then I see how it would need one. I didn't think a breaker panel screwed to a post was a structure.
Thanks for the help.

FWIW There was a recent code change (forget which year) where they added the words "other than equipment" to the definition of "structure"

 

[tom baker]

Ground rods are for lightning. Your panel could get hit, same as your house or shop

 

[augie47]

With the change electrofelon notes, it's a grey area at best but, as Tom states, it could prove useful and there is certainly no reason not to have it,

 

[Poweranytime]

My understanding is it wouldn't be required at the post with the equipment but at the house being a separate structure you would need a shut off outside and the electrodes and inter system Bridge would be required at this equipment. No 2020 in front of me but believe 250.94 and 250.32

 

[jaggedben]

Ground rods are for lightning. Your panel could get hit, same as your house or shop

Seriously, what good will any ground rods do if a lightning strike happens within the triangle of those three locations? I think 'ground rods are for lightning' is mostly a myth.

 

[tom baker]

Seriously, what good will any ground rods do if a lightning strike happens within the triangle of those three locations? I think 'ground rods are for lightning' is mostly a myth.

A cell tower can take a direct hit and survive, one I had installed had 4 10 ft rods connected by 2/0 cu.

 

[electrofelon]

Seriously, what good will any ground rods do if a lightning strike happens within the triangle of those three locations? I think 'ground rods are for lightning' is mostly a myth.

A cell tower can take a direct hit and survive, one I had installed had 4 10 ft rods connected by 2/0 cu.

I did a few cell towers like 15 years ago. Yes very elaborate grounding, there were a lot more than 4 rods on the ones I did (must have been dozens) with everything cad welded together - tower, ice bridge, fence, etc. I am also skeptical that all that earthing does much. Seems to me that the bonding is what is important, just to reduce damage from lighting jumping across different parts.

 

[LarryFine]

I did a few cell towers like 15 years ago. Yes very elaborate grounding, there were a lot more than 4 rods on the ones I did (must have been dozens) with everything cad welded together - tower, ice bridge, fence, etc. I am also skeptical that all that earthing does much. Seems to me that the bonding is what is important, just to reduce damage from lighting jumping across different parts.

Same here, in all points.

 

[jaggedben]

A cell tower can take a direct hit and survive, one I had installed had 4 10 ft rods connected by 2/0 cu.

Yeah, I mean, that actually kinda illustrates my point. To be clear, when I said 'mostly a myth' I meant with respect to NEC requirements. Here you talk about a (presumably) metal tower with grounding well in excess of NEC requirements. So, what's the point? Is the advice to the OP to install 4 10 ft rods connected by 2/0 cu?

As best I can tell, NEC grounding requirements are equally aimed at high-voltage faults to low voltage wires, open neutrals, and lightning, but actually provide paltry protection against all three. I suppose there's a fine line between using those justifications to encourage people to follow the code, and giving people who drive ground rods a false sense of security.

 

[Joe.B]

I recently saw plans for a house with a detached ADU, each building has a Ufer (CEE) ground and the feeder to the ADU was UF trenched over. The owner is an engineer of some sort and he stamped his own plans but is hiring a contractor to do the build. In addition to the two Ufer grounds he called out an additional piece of #4 copper to connect the two Ufer's at the bottom of what will be the feeder trench. Apparently he wants to make sure that the two grounding electrodes stay at the same voltage potential? Anybody ever heard of something like this? See any problems with this? Thanks.

 

[Dennis Alwon]

It is more than just lightning it is also for power surges.

 

[ActionDave]

I recently saw plans for a house with a detached ADU, each building has a Ufer (CEE) ground and the feeder to the ADU was UF trenched over. The owner is an engineer of some sort and he stamped his own plans but is hiring a contractor to do the build. In addition to the two Ufer grounds he called out an additional piece of #4 copper to connect the two Ufer's at the bottom of what will be the feeder trench. Apparently he wants to make sure that the two grounding electrodes stay at the same voltage potential? Anybody ever heard of something like this? See any problems with this? Thanks.

It's fine. In the context of this thread it is the same thing that they do on cell sites.

 

[ActionDave]

Yeah, I mean, that actually kinda illustrates my point. To be clear, when I said 'mostly a myth' I meant with respect to NEC requirements. Here you talk about a (presumably) metal tower with grounding well in excess of NEC requirements. So, what's the point? Is the advice to the OP to install 4 10 ft rods connected by 2/0 cu?

As best I can tell, NEC grounding requirements are equally aimed at high-voltage faults to low voltage wires, open neutrals, and lightning, but actually provide paltry protection against all three. I suppose there's a fine line between using those justifications to encourage people to follow the code, and giving people who drive ground rods a false sense of security.

You just summed up all the cognitive dissonance that exists in art. 250.

 

[jaggedben]

I recently saw plans for a house with a detached ADU, each building has a Ufer (CEE) ground and the feeder to the ADU was UF trenched over. The owner is an engineer of some sort and he stamped his own plans but is hiring a contractor to do the build. In addition to the two Ufer grounds he called out an additional piece of #4 copper to connect the two Ufer's at the bottom of what will be the feeder trench. Apparently he wants to make sure that the two grounding electrodes stay at the same voltage potential? Anybody ever heard of something like this? See any problems with this? Thanks.

My guess is that in case of lightning causing a voltage gradient in the ground he is trying to encourage the charge to take a path that is other than through the feeder conduit. Causes no problems if everything else is to code.