# Transformer ground issue. Need advice on location



## Sparko (Jan 21, 2015)

I am installing a 30 kva 480 to 120/208 3 phase transformer. I have no issues with over current sizing, bonding X0, etc. the issue is the location of the installation and where to ground. 

The transformer is going to feed a small weld shop. The structure it is in is solid concrete (walls, floor, ceiling, etc). I'm not sure what's below the floor and it's possible it's concrete 20' down. There is a single water pipe in another room that I can reach if I bore through the wall (there are no water pipes in my room, just an old cast iron sewer pipe). The walls have rebar and I believe the floor does too. There is no exposed structural metal that I can find to bond to. The current 480 panel I am tapping for the xfmr feed contains to ground conductor, only the conduit and panel is grounded (as expected). 

I am at a loss. The xfmr and all branch are done and ready to fire up but I must have a good ground before I can do this. My best guess is to drill into the floor with my hammer drill to see if I can hit dirt (I can go 18"). Little nervous about that as I don't know exactly what's below with locating service. If there is dirt, I'm not worried about the electrode being the 25 ohm required resistance because of the water content of the ground here. 

Anyone who may have had a similar experience or have any suggestions it would be greatly appreciated.


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## RIVETER (Sep 26, 2009)

The source of your transformer is where I would look. What feeds the distribution switch...and is there an "earth" ground present? If you can drive a rod, in addition, there is nothing wrong with that.


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## don_resqcapt19 (Jul 18, 2010)

If you drive a rod you will need two unless you can prove by testing that the one is 25 ohms or less. 
The inspectors in many areas require that you run a GEC back to the service grounding electrode for applications like this.


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## chicken steve (Mar 22, 2011)

Welcome to ET Sparko. 

Does your entire install originate within one structure here?

~CS~


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## ponyboy (Nov 18, 2012)

What about building steel, what's directly above the panel room for a ceiling? I'd drill through the wall so I could hit the main water line. It is the main incoming lime right?


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## Sparko (Jan 21, 2015)

riveter - I'm know there is an earthground at the source. So if I can get back to the source with an appropriate sized GEC, I can use that earth source? I know the main GEC must be in it's own dedicated conduit. That wouldn't really be an option since I would have to bury pipe in concrete over what might possibly be over a 100' distance. 

don- are you saying I should drive two rods as well as a GEC to the source of the panel? Fishing a ground conductor back to the source shouldn't be an issue. My main concern is the initial system ground (how to get a ground electrode established in this building). I also know they always recommend two rods 8' deep and no closer than 6' to each other. I've also understood that the second rod isn't a requirement but a failsafe to ensure the 25 ohm reading. 

chicken - no, the 480 source comes from another location with rigid buried in the concrete. All does not originate in the building. 

ponyboy - building steel isn't an option. it's all 12" of concrete with rebar in the center. Don't see how I could get to any structural steel. As for the water pipe, I can use that as my primary electrode? I believe the code is within 5' of entrance into the building. Correct me if I'm wrong, but it was my understanding, the reason we bond to a pipe (in a residence for instance) is not to use the pipe as an electrode (even though it may act as one), but to bond the water pipe in the residence to the system ground thereby protecting from any water pipe or fixtures inadvertently becoming energized in case of contact with an ungrounded conductor? Hence the reason for the jumper around a water meter in a utility-fed home.


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## Sparko (Jan 21, 2015)

Interpretation? As I read it, this code excerpt below means I can use the water pipe as a primary grounding electrode? Furthermore, in an industrial or commercial setting I can bond it to the pipe at a location further than 5 feet from entry into the building. Please correct me if I am misinterpreting this code? 

"You must terminate the grounding electrode conductor to a grounding electrode that's located as close as practicable to, and preferably in the same area as the nearest *effectively grounded metal member of the structure or effectively grounded metal water pipe within 5 ft from the point of entrance into the building*.

However, the grounding electrode conductor can terminate at any point on the water pipe system for industrial and commercial buildings where conditions of maintenance and supervision ensure only qualified persons service the installation, and the entire length of the interior metal water pipe used for the grounding electrode is exposed.


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## RIVETER (Sep 26, 2009)

Sparko said:


> Interpretation? As I read it, this code excerpt below means I can use the water pipe as a primary grounding electrode? Furthermore, in an industrial or commercial setting I can bond it to the pipe at a location further than 5 feet from entry into the building. Please correct me if I am misinterpreting this code?
> 
> "You must terminate the grounding electrode conductor to a grounding electrode that's located as close as practicable to, and preferably in the same area as the nearest *effectively grounded metal member of the structure or effectively grounded metal water pipe within 5 ft from the point of entrance into the building*.
> 
> However, the grounding electrode conductor can terminate at any point on the water pipe system for industrial and commercial buildings where conditions of maintenance and supervision ensure only qualified persons service the installation, and the entire length of the interior metal water pipe used for the grounding electrode is exposed.


Just keep in mind that the 5 foot designation for a connection was there to try as best you can to make that connection on the line side of the water disconnect.


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## minichopper6hp (Apr 19, 2014)

Take your sds and plunge into the slab. Chances are ia probably no more than a foot deep


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## Sparko (Jan 21, 2015)

minichopper6hp said:


> Take your sds and plunge into the slab. Chances are ia probably no more than a foot deep


well, my plan is to run back down with hammerdrill in hand, enough emt to run over to the water pipe, and a variety of spline bits. I'll bond to the water pipe, then, for sure. Probably run a second ground back to the source of the 480 (since this is a very old installation the only thing they ran over in the rigid was 3 conductors for the 480) and ground it there as well (this is assuming I can get through the pipe which I don't expect to have issues), finally (it's unsure because I'm not 100% what I'm drilling through, but I'll attempt to bore a hole through the floor for the grounding rod. If I can get through it and find dirt I'll drive it in and use it. If not, I guess I'll have to see if the water pipe and ground back to the source will pass. Sound like a plan?


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## Pete m. (Nov 19, 2011)

This may also be an option from the 2014 NEC:

*250.121 Use of Equipment Grounding Conductors.* An 
equipment grounding conductor shall not be used as a 
grounding electrode conductor. 

_Exception: A wire-type equipment grounding conductor in-
stalled in compliance with 250.6(A) and the applicable re-
quirements for both the equipment grounding conductor 
and the grounding electrode conductor in Parts II, III and 
VI of this article *shall be permitted to serve as both an 
equipment grounding conductor and a grounding electrode 
conductor.*_ 

Pete


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## don_resqcapt19 (Jul 18, 2010)

Pete m. said:


> This may also be an option from the 2014 NEC:
> 
> *250.121 Use of Equipment Grounding Conductors.* An
> equipment grounding conductor shall not be used as a
> ...


That is really no different than it was prior to the 2011 code. There is absolutly no need for 250.121. If you want to use a single conductor to serve both purposes it always had to meet the requirements for both. As it stands now, the only code that says you can't use a common conductor is 2011.


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## B-Nabs (Jun 4, 2014)

I think I would check into the feasibility of driving ground rods first, and if it works out you're done. I would only look at the water pipe and/or running back to the 480 source as secondary options.


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## Pete m. (Nov 19, 2011)

don_resqcapt19 said:


> That is really no different than it was prior to the 2011 code. There is absolutly no need for 250.121. If you want to use a single conductor to serve both purposes it always had to meet the requirements for both. As it stands now, the only code that says you can't use a common conductor is 2011.


Thank you for bringing that up. I may have been approaching this incorrectly for some time. Thankfully, the typical installation I'm used to seeing employs two separate means.

I concede that there was no verbiage prior to the 2011 NEC that specifically prohibited using one for the other if all applicable sections were complied with but I have always approached the two conductors as having separate purposes and separate requirements basing this thought out of article 100. 

Pete


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## chicken steve (Mar 22, 2011)

Sparko said:


> well, my plan is to run back down with hammerdrill in hand, enough emt to run over to the water pipe, and a variety of spline bits. I'll bond to the water pipe, then, for sure. Probably run a second ground back to the source of the 480 (since this is a very old installation the only thing they ran over in the rigid was 3 conductors for the 480) and ground it there as well (this is assuming I can get through the pipe which I don't expect to have issues), finally (it's unsure because I'm not 100% what I'm drilling through, but I'll attempt to bore a hole through the floor for the grounding rod. If I can get through it and find dirt I'll drive it in and use it. If not, I guess I'll have to see if the water pipe and ground back to the source will pass. Sound like a plan?


As far as i can read , your GRC is an EGC to an SDS. All you need is/are the GEC's made from XO Spark

The main h20 pipe is , iirc, prerequisite to initial poco being introduced, so if you're the first to power this structure you're GEC should land within the 5's mentioned prior

*IF* the structure is already energized, you may hit the main h20 pipe proximal to your Xfomer's XO 

Others hopefully will chime in.....:thumbsup:

~CS~


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## don_resqcapt19 (Jul 18, 2010)

Pete m. said:


> Thank you for bringing that up. I may have been approaching this incorrectly for some time. Thankfully, the typical installation I'm used to seeing employs two separate means.
> 
> I concede that there was no verbiage prior to the 2011 NEC that specifically prohibited using one for the other if all applicable sections were complied with but I have always approached the two conductors as having separate purposes and separate requirements basing this thought out of article 100.
> 
> Pete


There are a lot of requirements for the installation of the GEC that makes using a single conductor for both a GEC and an EGC difficult and I believe that is why you rarely see a conductor that serves both purposes.


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## don_resqcapt19 (Jul 18, 2010)

If you provide a grounding electrode system at the transformer you still have to connect that grounding electrode the main building grounding electrode.
The rules for the bonding connection between grounding electrodes are not as hard to comply with as the rules for the GEC. I think you can use the EGC as the bonding connection.


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