# Permanently mounted Generator grounding question



## HARRY304E (Sep 15, 2010)

mkc62 said:


> I’m helping a co-worker upgrade the electrical in an old cabin he bought. Most of my work is industrial and don’t do much residential generator work. In reading the NEC, sections 250.6 , its getting a bit confusing. In doing searches here on this forum I also see all sorts of answers.
> 
> The work involves a new 200A service with 100A Sub panel (taking the place of an old large fuse box) also upgrading an old 60A generator transfer switch to match the 100A subpanel. My attached sketch below should clearly show the layout.
> 
> ...


Here is your sketch..Welcome to the forum..:thumbup:


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## HARRY304E (Sep 15, 2010)

That conduit run is it RMC or PVC?


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## Roger123 (Sep 23, 2007)

If you can not use the conduit as an EGC, then 250.32(B)(1) exception may apply.


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## mkc62 (Jun 30, 2012)

HARRY304E said:


> Here is your sketch..Welcome to the forum..:thumbup:



Thank you sir....must be something wrong on both my home and work computer, all I see is the little red *x* but I can see other peoples pics and schematics....does one need to create an album here at this forum then link from there? I do see there is a picture section, just not under the users control page.

As for the conduit, it is RMC in the gen shed, but at the basement end its PVC. All of this was probably done over 20 years ago.

let me see if we agree on this laymans interpretation of 250.32(b)(1)

Because my OLD gen wiring is existing, AND it meets ALL the requirements of 1,2,3 (under the exception clause)...Then the fact that my neutral from the Gen is non switched/Bonded via the new 200A's Supply neutral leg, I'm ok?


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## gottspeed (Mar 8, 2010)

Well without looking at the code that looks ok to me, its the same way service comes from a pole or to a garage with no bond, except that if that 100 amp panel is only connected by itself when the xfer switch throws then I might bond the neutral to ground there.


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## mkc62 (Jun 30, 2012)

If I bond the constant neutral to the separate ground bus in the Transfer switch, would that still be deemed as a separate ground and neutral at a sub location? ...or does that rule only apply to the 100A Sub load center?


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## Roger123 (Sep 23, 2007)

mkc62 said:


> If I bond the constant neutral to the separate ground bus in the Transfer switch, would that still be deemed as a separate ground and neutral at a sub location? ...or does that rule only apply to the 100A Sub load center?


Only bond the neutral at the first disconnect, which you have labeled as your primary 200 main panel. Since you are not switching the neutral at the transfer switch it stays isolated at the transfer switch and the sub-panel.


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## mkc62 (Jun 30, 2012)

Thanks....and that is the way I have it right now.

As for the new ground rod I drove at the generator building. My plan there is to bond that to chassis of the Gen. I need to check if internally of the GEN the neutral is bonded to chassis. I am told a lot of Gens are that way.

I'm assuming the exception 250.32(B)(1), will cover me against having to pull a new ground between the gen and the transfer. That being my original question. Ultimately I guess its whatever the inspector wants to see.


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## ceb58 (Feb 14, 2009)

mkc62 said:


> Thanks....and that is the way I have it right now.
> 
> As for the new ground rod I drove at the generator building. My plan there is to bond that to chassis of the Gen. I need to check if internally of the GEN the neutral is bonded to chassis. I am told a lot of Gens are that way.
> 
> I'm assuming the exception 250.32(B)(1), will cover me against having to pull a new ground between the gen and the transfer. That being my original question. Ultimately I guess its whatever the inspector wants to see.


It will be a coin toss. Since there has been an upgrade he could site 250.35


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## WarAdmiral (Jul 13, 2012)

Yes you will create a potential difference if no ground is pulled. If I ran a 30 amp line to a generator it would be a 10/3 rx and use an l14-30 receptical or a PB30. My point being is size big or small it's all the same regardless of plug in or hard piped.


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## B4T (Feb 10, 2009)

I thought the gr. rod was not necessary and up to AHJ.. :blink::blink:


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## WarAdmiral (Jul 13, 2012)

If this is a permanent installed unit an is sitting on a concrete pad that pad must be grounded to have equal potential. In this case you will need to use a ground rod


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## mkc62 (Jun 30, 2012)

After my last post, I went and talked to local code office chief inspector. His reply was such.

There is no grandfathering pertaining to any old wiring, 4 wires is all that will be accepted in this county. This was the case whether the generator was permanant or Mobile. He did suggest the local ground rod in the event of a permanent installation. I suggested a direct bury ground wire, which was acceptable but they needed to see the 18' deep trench prior to the final. If I am going to do that I might as well just lay all new conduit and all new wire and have it done proper. Pulling all new was what we were trying to avoid.

One thing I have come to find out on this topic, whether it be here on this forum, talking to local master electrician, or talking to the local code people. Everybody seems to have a different opinion as to how it should be done or accepted. So much for code and consistency.

Our plan now is to stub out a new external to the main structure, power inlet box which is at best a 20' conduit and wiring run. With intent of future generator at that location. This will satisfy the inspector for the service change. If homeowner later wants to reconnect his old wiring to his old generator, that is his decision.


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