# Supplementary ground rod



## ohmdoctor (Oct 5, 2007)

RIVETER said:


> I have always thought that the EGC and the GEC were for two completely different purposes. I still believe they are, but am trying to understand why the code would maintain that if you have a service to a building supplied from a FIRST building , that in that case, if you had only one grounding electrode at the second building, that the EGC from the first to the second would be allowed to be used for a supplementary ground. Or did I mis- read?


 
Although this a separate structure and must be grounded in accordance with 250.32 it is not a separately derived system so the equipment grounding conductor which is brought over with the buildings feeders can be used as a supplemental ground for that building. Also the buildings ground would only need to sized from 250.122 not 250.66 per 250.32(B)


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## RIVETER (Sep 26, 2009)

ohmdoctor said:


> Although this a separate structure and must be grounded in accordance with 250.32 it is not a separately derived system so the equipment grounding conductor which is brought over with the buildings feeders can be used as a supplemental ground for that building. Also the buildings ground would only need to sized from 250.122 not 250.66 per 250.32(B)


Thanks for responding. I am wondering the reasoning behind the decision to let a GEC be a conductor to a grounding electrode. If, by chance, a strike occurs at the second building and the first rod is not sufficient to take the strike, why send it into the first building's service... A place it may not have gone in the first place? Why not just drive another rod at the second building?


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## ohmdoctor (Oct 5, 2007)

RIVETER said:


> Thanks for responding. I am wondering the reasoning behind the decision to let a GEC be a conductor to a grounding electrode. If, by chance, a strike occurs at the second building and the first rod is not sufficient to take the strike, why send it into the first building's service... A place it may not have gone in the first place? Why not just drive another rod at the second building?




I agree with you I don't think this section is really addressing the hazard of a lightening strike. I think it's more just for grounding the system for ground faults... I'm not sure though out here in Ca, we don't deal with very many lightening strikes and aren't required to make provisions for it in most cases.
I don't think it would hurt to add an extra ground rod in any case!! But sense the second dwelling is derived from the main service of that property the entire grounding system has to be continues... If one building goes down they both go....


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## Bob Badger (Apr 19, 2009)

OK first things first, if you want to talk about NEC grounding and bonding requirements you really need to use the NEC terms or we will be talking in circles.

You called this thread ...



> Supplementary ground rod


Well to the NEC a Supplementary ground rod is an electrode as described by 250.54 it is now called an auxiliary electrode and it has nothing at all to do with a second building.



> *250.54 Auxiliary Grounding Electrodes.* One or more
> grounding electrodes shall be permitted to be connected to
> the equipment grounding conductors specified in 250.118
> and shall not be required to comply with the electrode
> ...


Auxiliary (or Supplementary) Grounding Electrodes are any electrodes that someone decides to add for any reason at all, they are not required by the NEC but they are permitted. They can be rods, plates, rings even a metal folding chair could be a Auxiliary (or Supplementary) Grounding Electrodes. There are no specifications other than they can only be connected to the Equipment Grounding Conductor, never to the neutral.

The ground rod some engineers require at a site lighting base would be an Auxiliary (or Supplementary) Grounding Electrode.

So moving on.




RIVETER said:


> I have always thought that the EGC and the GEC were for two completely different purposes. I still believe they are,


There are.




> but am trying to understand why the code would maintain that if you have a service to a building supplied from a FIRST building , that in that case, if you had only one grounding electrode at the second building, that the EGC from the first to the second would be allowed to be used for a supplementary ground. Or did I mis- read?



OK, except for a specific exception you cannot have a 'service' to a building supplied from a first building.

You can have a 'service' in the first building and a feeder to the second building.

At the second building you will be required to provide a Grounding Electrode System (GES) and under the 2008 NEC that will connect to the Equipment Grounding Conductor at the second building.



> *250.32 Buildings or Structures Supplied by a Feeder(s)
> or Branch Circuit(s).*
> (A) Grounding Electrode. Building(s) or structure(s) supplied
> by feeder(s) or branch circuit(s) shall have a grounding
> ...


These are not supplemental, supplementary or an auxiliary electrodes, they are just electrodes.

This grounding electrode system at the second building is aimed at keeping the lighting strike at the second building.

But it cannot do that, part of the strike current is always going to head back to the first building. The electrons go all directions available.


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## McClary’s Electrical (Feb 21, 2009)

RIVETER said:


> Thanks for responding. I am wondering the reasoning behind the decision to let a GEC be a conductor to a grounding electrode. If, by chance, a strike occurs at the second building and the first rod is not sufficient to take the strike, why send it into the first building's service... A place it may not have gone in the first place? Why not just drive another rod at the second building?


 

Please use the correct terms before you confuse yourself


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## jwjrw (Jan 14, 2010)

I believe if you only pull a 3 wire to the seperate structure no additional ground rod is required at it.


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## Bob Badger (Apr 19, 2009)

jwjrw said:


> I believe if you only pull a 3 wire to the separate structure no additional ground rod is required at it.


Up until the 2008 NEC, under some conditions, you had a choice to run a separate EGC, or not to with the feeder to a separate building or structure.

But either way, the NEC has required an grounding electrode system at the separate building or structure for a long, long, time.


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## jwjrw (Jan 14, 2010)

Bob Badger said:


> Up until the 2008 NEC, under some conditions, you had a choice to run a separate EGC, or not to with the feeder to a separate building or structure.
> 
> But either way, the NEC has required an grounding electrode system at the separate building or structure for a long, long, time.



I know that....I'm talking a 3wire branch circuit that is considered a single circuit and no ground rod needed.


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## Bob Badger (Apr 19, 2009)

jwjrw said:


> I know that....I'm talking a 3wire branch circuit that is considered a single circuit and no ground rod needed.


In case of a single branch circuit no electrode is needed as you are pointing out. :thumbsup:


However a mulitiwire branch circuit is a 'single circuit' so the branch circuit could be 3, 4 or even 5 wire and not require a grounding electrode.


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## RIVETER (Sep 26, 2009)

My original post was as a result of reading portions of older code information. I can't find it now but I remember...only because I had written it down, that it was Art. 250.56 but was the 2002 cycle, I think. I remember it saying that the egc from the first building could be used as the supplemental grounding electrode for the second. Whether or not I am remembering it correctly, what I am getting at is that I don't think it is a good idea at any time unless possibly the egc would be a metallic conduit system which could dissipate the strike energy before entering the first building.


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## RIVETER (Sep 26, 2009)

mcclary's electrical said:


> Please use the correct terms before you confuse yourself


Tell me where I am confused in that statement.


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## wayne g (Nov 28, 2010)

In a out Building EGC pulled is a good thing, also GEC is required and has been the case for many years.


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## raider1 (Jan 22, 2007)

wayne g said:


> In a out Building EGC pulled is a good thing, also GEC is required and has been the case for many years.


Under the 2008 NEC not only is it a good thing to pull an EGC to a detached building it is a code requirement.

Chris


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## wayne g (Nov 28, 2010)

raider1 said:


> Under the 2008 NEC not only is it a good thing to pull an EGC to a detached building it is a code requirement.
> 
> Chris


Thanks for the info, but Ct is still under the 05 NEC


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## wayne g (Nov 28, 2010)

raider1 said:


> Under the 2008 NEC not only is it a good thing to pull an EGC to a detached building it is a code requirement.
> 
> Chris


Thanks for the info, but the state of CT is behind the times we are still under the 2005 NEC.


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## McClary’s Electrical (Feb 21, 2009)

wayne g said:


> Thanks for the info, but the state of CT is behind the times we are still under the 2005 NEC.


 

Wayne, how is this any different than the post before?


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## robnj772 (Jan 15, 2008)

Gee what a surprise

ANOTHER old thread bumped by wayne g


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