Vehicle Mounted Generator - Construction Office Trailer

[moosecreek86]

I wanted to get this clear once and for all. I have re-visited this topic several times and seems like a huge grey area to me. Mike Holt mentions in bonding and grounding video that he would not install a vehicle mounted generator to temporary office construction trailer to code, and that he would absolutely violate code 250.6.


He mentions that if One-Hundred electricians removed the system bonding jumper how many of them would put it back when generator is no longer needed.


The Code guy on his panel mentions that when you have a feeder to a temporary building that it becomes a separately derived system and that by not removing Bonding jumper goes against code 250.6 Objectionable Current.

I am so confused on this topic, all I want to do is install this generator to be as electrically safe as possible.

The way I see it is, I would ground the Generator and not the temporary building because the generator is where the neutral and ground are boded together. Correct me if I'm wrong.

Attached are phots of exactly what I am dealing with. Any help is greatly appreciated.

Thanks,

 

[zbang]

People get a bit fussy about the terminology, I'll assume "ground the generator" means install a grounding electrode system (GES).

It's almost always the case that a feeder supplies the trailer, and that feeder should have separate neutral and ground conductors. You only want a bonding jumper at the trailer if that's the service disconnect (really unlikely, panel probably isn't rated as a service equipment anyway).

Neutral/ground bond - at the generator, not the trailer. At least half the generators I see already have one, and almost always on the CS connectors.

Grounding electrode (rods) - at the trailer because it's a "structure", scholars differ as to whether the trailer-mounted generator needs one, but since that's next to the trailer, also run a GEC from the rods to the trailer frame.

 

[moosecreek86]

People get a bit fussy about the terminology, I'll assume "ground the generator" means install a grounding electrode system (GES).

It's almost always the case that a feeder supplies the trailer, and that feeder should have separate neutral and ground conductors. You only want a bonding jumper at the trailer if that's the service disconnect (really unlikely, panel probably isn't rated as a service equipment anyway).

Neutral/ground bond - at the generator, not the trailer. At least half the generators I see already have one, and almost always on the CS connectors.

Grounding electrode (rods) - at the trailer because it's a "structure", scholars differ as to whether the trailer-mounted generator needs one, but since that's next to the trailer, also run a GEC from the rods to the trailer frame.

This makes perfect sense. I did speak with an inspector friend of mine and he mentions to have the GES/ Grounding electrode hooked to the generator and a separate ground rod for the office trailer frame for lightning reasons. Does this sound right?

The small panel is not service disconnect rated. It is a direct termination to some aluminum lugs that are probably not even rated for fine strand DLO cable. Um idk, haha I'm given some interesting parts to deal with. There are several other code violations like not having proper CGB connectors for SO cable, Lugs, wire identification, and workmanship etc..

I guess all I care about at this point is to have an effective ground fault current path. So I am running the GEC directly to the Generator.

Thanks for your help.

 

[don_resqcapt19]

I would treat it like a service, even though that is a code violation. I would leave the bond in the generator, and have a grounding electrode connection and a system bonding jumper in the trailer. I see very little difference in the hazard either way. There would only be hazard if the neutral conductor is open between the generator and the trailer. The locations of the system bonding jumper and the grounding electrode do little to change the hazard.

 

[don_resqcapt19]

...
I guess all I care about at this point is to have an effective ground fault current path. So I am running the GEC directly to the Generator.

Thanks for your help.

The grounding electrode and GEC have nothing to do with an effective ground fault current path. That path is what ever path that provides a connection between the generator neutral and the equipment grounding conductors.

 

[ActionDave]

The Code guy on his panel mentions that when you have a feeder to a temporary building that it becomes a separately derived system and that by not removing Bonding jumper goes against code 250.6 Objectionable Current.

Think about this. Where is the objectionable current traveling when the connection between the building and the generator when all you have between them is a rubber cord?

I am so confused on this topic, all I want to do is install this generator to be as electrically safe as possible.

The way I see it is, I would ground the Generator and not the temporary building because the generator is where the neutral and ground are boded together. Correct me if I'm wrong.

Grounding and bonding gets much easier to understand when you begin to treat connections to earth as useless voodoo and start thinking of terms of how to clear a fault.

 

[ActionDave]

I would treat it like a service, even though that is a code violation. I would leave the bond in the generator, and have a grounding electrode connection and a system bonding jumper in the trailer. I see very little difference in the hazard either way. There would only be hazard if the neutral conductor is open between the generator and the trailer. The locations of the system bonding jumper and the grounding electrode do little to change the hazard.

I agree.

 

[moosecreek86]

Think about this. Where is the objectionable current travelling when the connection between the building and the generator when all you have between them is a rubber cord?



Grounding and bonding gets much easier to understand when you begin to treat connections to earth as useless voodoo and start thinking of terms of how to clear a fault.

This puts things into a great perspective. I will try to be more conscious of this. Thanks for the insight.

 

[moosecreek86]

The grounding electrode and GEC have nothing to do with an effective ground fault current path. That path is what ever path that provides a connection between the generator neutral and the equipment grounding conductors.

This is also making some sense to me. I am currently studying Mike Holts electrical theory book. I purchased his complete 2017 ultimate library and I remember something about how fault current returns to the power supply via a equipment bonding jumper.

 

[moosecreek86]

This is the final result if anyone is curious. I feel like this was such a simple installation but I ended up getting caught up with the electrical theory and trying to understand how and why.

This being my first post, I will say I learned a lot. My language was all over the place including acronyms. I laugh at myself now that I re-read complete thread. I will get better at the precise language describing things. I guess I was in a hurry and not quite thinking straight. I appreciate all the feedback I truly do.

Thanks again,

 

[david]

People get a bit fussy about the terminology, I'll assume "ground the generator" means install a grounding electrode system (GES).

It's almost always the case that a feeder supplies the trailer, and that feeder should have separate neutral and ground conductors. You only want a bonding jumper at the trailer if that's the service disconnect (really unlikely, panel probably isn't rated as a service equipment anyway).

Neutral/ground bond - at the generator, not the trailer. At least half the generators I see already have one, and almost always on the CS connectors.

Grounding electrode (rods) - at the trailer because it's a "structure", scholars differ as to whether the trailer-mounted generator needs one, but since that's next to the trailer, also run a GEC from the rods to the trailer frame.

IMO job trailers get supplied as indicated in article 550.4(A) in your case simplifies the grounding issue and instillation of the GES, and feeder to the job trailer

 

[tom baker]

Regarding terms and language for grounding...
"we have met the enemy and he is us" Pogo
the term ground is used mostly incorrectly, by us. I need to pull a ground, or what size ground?
Mike Holt once said what color is it and what does it do?