Ground rod for stand alone refrigeration units

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kwired said:
But it is a stand alone and presumably portable thing. There are millions of refrigerated trucks/trailers out there that have onboard generator as well as shore power capability and they don't drive ground rods, kind of hard to when on the move. Other than the direct lightning strike, only other time there is an issue is nearby strike and some transient current entering via the shore power connection, which is what you have with other buildings connected to the grid. A lot of lightning damage in permanent buildings comes from nearby strikes. Direct strike is likely to have damage whether there is a grounding electrode or not.

Permanent buildings/structures don't require a grounding electrode is supplied by a branch circuit. They do if feeder or service supplied.
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Trucks and Associated trailers are not covered by the national electrical code though so if you are talking about a truck and trailer it is a moot point. I got the impression from the original poster that it was a cargo container sitting on the ground and not a trailer.
 
MotoRand said:
I understand that the circuit bonding is good.

I think there is a need for a ground rod for possible lightening strikes, or similar overvoltage problems. My concern is that there will be people coming in and out of this loading and unloading several times a day, so I would like to be sure there is a good path to ground, in case of lightning. The container is metal, so that does help with the grounding issues.
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By this logic, all of these shipping containers need grounding electrodes. You may notice none of them have them.

A ground rod is not a lightning protection system and will serve no real purpose in your situation. The equipment grounding conductor connected back to the service you are supplied from will be connected to a grounding electrode system that provides protections against overvoltage and lightning coming from elsewhere. For direct strikes of either, a ground rod isn't going to do diddly squat. I think it's debatable whether your container is a 'structure' or whether it is 'installed'. If it is neither of those things then the NEC doesn't require a grounding electrode and may not even cover it at all. It seems like you are creating unnecessary work and expenses for other people.
 
I would point out that the code does not have an exception to following the rules just because they don't serve any useful purpose. Nor because most people ignore certain rules.
 
petersonra said:
Trucks and Associated trailers are not covered by the national electrical code though so if you are talking about a truck and trailer it is a moot point. I got the impression from the original poster that it was a cargo container sitting on the ground and not a trailer.
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I guess I had impression it was portable and trailer kind of comes to mind, but yes if it is not a trailer and is supplied with a feeder it should need it's own GES.

Sahib said:
Art.100. Definition for ground in earlier code cycles:a conducting body may serve as ground.
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How long ago?

Actually 250.52(A)(2)(1) does qualify this as a grounding electrode if it is in contact with earth for 10 feet or longer. Sitting on concrete probably not, embedded in concrete yes.
 
petersonra said:
It is both a structure and has a generator. Both situations require a grounding electrode system. In my opinion a stand-alone walk-in freezer that is not connected to the building as a separate structure and if it's fed by more than one branch circuit requires a grounding electrode system.
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I don't see this as a structure, I view it as equipment. I am not saying I am right or that you are wrong. That is the rub of the issue here.
 
Strathead said:
I don't see this as a structure, I view it as equipment. I am not saying I am right or that you are wrong. That is the rub of the issue here.
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If it is stand alone and away from structure it is supplied from, it is more likely to be supplied with a branch circuit, which case it wouldn't require a GES anyway. If it is supplied via a feeder, it gets more questionable whether a GES is needed.
 
system grounding/bonding

system grounding/bonding

I thought it might help to share a picture of the prototype system. It is a 20' by 8' container with an on board generator/refrigeration system. My concern is that when it is running off of the on board generator, there is no ground rod source. If it is connected to shore power or a generator micro grid, there is a grounding (ground rod or other) system, but not with the on board generator. A similar system has been made over the past several years, that doesn't have a ground rod. I feel we should include one, since this system would be set up in military camps for an indeterminate time period.

MTRCS.jpg
 
MotoRand said:
I thought it might help to share a picture of the prototype system. It is a 20' by 8' container with an on board generator/refrigeration system. My concern is that when it is running off of the on board generator, there is no ground rod source. If it is connected to shore power or a generator micro grid, there is a grounding (ground rod or other) system, but not with the on board generator. A similar system has been made over the past several years, that doesn't have a ground rod. I feel we should include one, since this system would be set up in military camps for an indeterminate time period.

View attachment 22396
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I myself would be more concerned about bonding adjacent units to one another to reduce any touch potential between them than I would be concerned about driving ground rods. If far enough apart you can't touch both at same time, they are fine as equipped.
 
MotoRand said:
I thought it might help to share a picture of the prototype system. It is a 20' by 8' container with an on board generator/refrigeration system. My concern is that when it is running off of the on board generator, there is no ground rod source. If it is connected to shore power or a generator micro grid, there is a grounding (ground rod or other) system, but not with the on board generator. A similar system has been made over the past several years, that doesn't have a ground rod. I feel we should include one, since this system would be set up in military camps for an indeterminate time period.

View attachment 22396
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And what do you expect the electricity to do? Name a scenario where current could find a path through a living body and back to the neutral building steel bonding point in the generator.
 
MotoRand said:
I thought it might help to share a picture of the prototype system. It is a 20' by 8' container with an on board generator/refrigeration system. My concern is that when it is running off of the on board generator, there is no ground rod source.
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How would this be different than a refrigerated truck parked at a rest stop?

If it is connected to shore power or a generator micro grid, there is a grounding (ground rod or other) system, but not with the on board generator. A similar system has been made over the past several years, that doesn't have a ground rod. I feel we should include one, since this system would be set up in military camps for an indeterminate time period.
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I agree with others, a ground rod isn't going to add any margin of safety.
 
I see no need for ground rods at all. Each self-contained unit is its own ground plane, so there would be no potential for a potential difference between a unit and earth.
 
MotoRand said:
I thought it might help to share a picture of the prototype system. It is a 20' by 8' container with an on board generator/refrigeration system. My concern is that when it is running off of the on board generator, there is no ground rod source. If it is connected to shore power or a generator micro grid, there is a grounding (ground rod or other) system, but not with the on board generator. A similar system has been made over the past several years, that doesn't have a ground rod. I feel we should include one, since this system would be set up in military camps for an indeterminate time period.
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When the unit is running with its onboard generator then the are no wires connecting it to far away sources of a high voltage such as lightning or damaged high-voltage wiring. To experience such conditions there would have to be a very direct strike on the unit, in which case !@#$ is going to happen whether there's a ground rod or not.

I think you have it backwards. The code permits portable generators to run without grounding electrodes, and (generally) requires permanent structures to have them.

The most convincing thing you have said in favor of a ground rod is 'an indeterminate time period'. That's the closest you've come to showing that this unit is 'installed' and perhaps should be considered a 'structure. Those are the criteria (if the unit is also fed by a feeder, and not just a branch circuit) that would trigger the NEC to require a grounding electrode. If it is 'portable' and running on its own power, or if it is just 'equipment' and not a structure, then the NEC doesn't require it.
 
We just got three ( 3 ) 30ft long of these containers in that look identical to these refrigeration units except they do not have a generator installed . My question I have is flexible seoow cord allowed to feed them if they are only temporary ? Supposedly these will be gone in 3 months . 3 phase 480 v , 30 amp feed to each one
 
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