Small Guard shack ground Rod debate

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brother

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Ran into an existing situation where they have a small guard shack (7x5 possibly) with a small 125amp panel with about 4 circuits in it (lights receptacle and special for air conditioner). They ran a 30 amp feeder to it, single phase 2 hots, neutral and ground.

I was under the impression since they ran more than 1 circuit to it and its technically a seperate structure and it sits out in the open in the weather in the parking lot, then it was suppose to have its own ground rod etc.. for lightning and overvoltages. Others say, no it does not since its just a small shack. Never thought the size made a difference for guard shacks. I dont have my code with me at the moment, but am I correct on this? NEC 2024 250 somewhere in there? Doubt if it gets changed, but just double checking myself. Am I correct on this?
 
roger said:
You are correct, 250.32
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Thanks. Not that its going to change anything, as these folks wont install it unless they get hit with an inspection.
roger said:
You are correct, 250.32
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I forgot to add, what was the reason they made an exception for single circuits or multiwire circuits when the original reason was for lightning and overvoltages? Does anyone know the history of that article?
 
GES is required at a panel and no one really knows why. If the structures are the same then their potential for a lightning strike, surges, etc. are the same. So one/two circuits or more I don't see any difference.
 
LarryFine said:
I believe it's because branch circuits originate from there.
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But what difference would it make if the supply to the same structure were a feeder or a branch circuit? Wouldn't the lightning or surge risk be the same?
 
infinity said:
But what difference would it make if the supply to the same structure were a feeder or a branch circuit? Wouldn't the lightning or surge risk be the same?
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Lightning abatement may not be the only reason for grounding electrodes. I think it's also attempting to re-establish a zero-volts-to-earth reference for the separate structure, like with services.

Before four-wire feeder rules, the same thing used to be done with feeeder neutrals. Many NEC rules were based on understanding at the time, and they haven't had a reason to change them.
 
LarryFine said:
Lightning abatement may not be the only reason for grounding electrodes. I think it's also attempting to re-establish a zero-volts-to-earth reference for the separate structure, like with services.
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I'm not sure that a separate structure fed by a 20 amp MWBC is any less safe than a separate structure fed by a 20 amp feeder to a panel. If it is then the NEC should require a GES for either scenario.
 
infinity said:
I'm not sure that a separate structure fed by a 20 amp MWBC is any less safe than a separate structure fed by a 20 amp feeder to a panel. If it is then the NEC should require a GES for either scenario.
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I'm just "mentally reverse-engineering" it. What I see that is physically and/or electrically different is the point of origin of the circuit(s) in question. The EGC originates where the EGC/GEC systems are bonded.

Again, this may have originated when three-wire feeders were the norm, and re-earthing the neutral at a remote structure/sub-panel seemed logical, like a service, and no good reason to change it ever arose.
 
LarryFine said:
Again, this may have originated when three-wire feeders were the norm, and re-earthing the neutral at a remote structure/sub-panel seemed logical, like a service, and no good reason to change it ever arose.
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It could be a holdover from the 3-wire feeder days but that ended over a decade and a half ago. My question is not really asking why do we have a GES when there is a panel at the separate structure it's why don't we require a GES when there is no panel.
 
infinity said:
My question is . . . why don't we require a GES when there is no panel.
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That's what I'm getting at; the GES is located at the panel where the circuit (and its EGC) originates.

The load end could be "carried around" like a cord, as long as it's grounded where it's "plugged in."
 
Would a the purpose of a GES not be to limit the touch/step potential between the earth and any exposed metal electrical enclosures?
 
tortuga said:
Would a the purpose of a GES not be to limit the touch/step potential between the earth and any exposed metal electrical enclosures?
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I used to think so, but it has been made clear to me by others here that it doesn't work that way.

There is no requirement that an electrode be installed at the remote panel or other enclosures.

And, the earth is not conductive enough locally for it to be effective in minimizing step potential.
 
When I was doing traffic signal work for the County of Los Angeles, we started converting our controllers from electromechanical to digital. We were installing "170 Controllers" which were all solid state. Our electrical service started on a utility pole and went underground to the controller where we installed a second ground rod. After installing several cabinets, we started getting calls that the intersections were going on "Flash". I discovered that there was a difference in potential between the two ground rods. So, I disconnected the second ground rod at the controller cabinet and pulled a grounding conductor back to the service, and that corrected the problems.

This was from my earlier post ... I thought this might apply, since we now have more sensitive electronic equipment that are tripping GFCI (Ground Fault Circuit Interrupters).
 
LarryFine said:
Lightning abatement may not be the only reason for grounding electrodes. I think it's also attempting to re-establish a zero-volts-to-earth reference for the separate structure, like with services.

Before four-wire feeder rules, the same thing used to be done with feeeder neutrals. Many NEC rules were based on understanding at the time, and they haven't had a reason to change them.
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But the GES does not do that...it simply raises the voltage of the earth for a small area round the electrode
 
Thanks for all the responses and insight. I am curious how others would interpret a light pole that has 'other circuits that spliced in it but continue to feed other poles, but only 1 circuit actually powers that specific pole light. Also another scenario, a circuit supplies the light on the pole but another circuit supplies other equipment on the same pole, for example a camera (including low voltage of 30volts), or some other equipment that has 120v or more. Is a GES still required?
 
brother said:
Thanks for all the responses and insight. I am curious how others would interpret a light pole that has 'other circuits that spliced in it but continue to feed other poles, but only 1 circuit actually powers that specific pole light. Also another scenario, a circuit supplies the light on the pole but another circuit supplies other equipment on the same pole, for example a camera (including low voltage of 30volts), or some other equipment that has 120v or more. Is a GES still required?
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I think poles are exempt from any GES requirements.
 
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