# Ideas for grounding transformer



## erics37 (May 7, 2009)

Remember this wall of s**t I posted a little while back?



















Well I'm starting that job soon. We're demoing EVERYTHING on that wall and starting from scratch. We're putting a new transformer up as well but therein lies my problem. The old transformer, as far as I can tell by a cursory glance, does not have a connection to grounding electrode(s). Well who cares, right? We're ripping it out and starting over. Even if it does have one (maybe poking out the back into the wall or something), it's certainly not compliant with current NEC.

The building is wood (no structural steel electrode) and there is no metal water pipe in the structure. It's basically just an electrical-only building. 250.30(A)(4) exception tells me that if those two electrodes are not present for my transformer secondary SDS then I can use any other type of electrode. Well this building is built on a concrete pier on pilings over the bay. Can't drive ground rods or dig in a ground plate or ground ring. What do y'all suggest? Should I have them trench out some concrete and lay a ufer in there and repour it? Anything easier? The pilings are all wood and the beams are all huge old timbers (old building).


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## D-Bo (Apr 15, 2012)

that's quite the clusterf*** you've got there. i like the ufer idea. might be on to something there


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## D-Bo (Apr 15, 2012)

this building have an ariel feed?


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## wildleg (Apr 12, 2009)

what's the building going to be used for ? how far to land ? how deep is the water ?


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## Bbsound (Dec 16, 2011)

Throw some copper in the water!!


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## erics37 (May 7, 2009)

D-Bo said:


> this building have an ariel feed?


Currently yes, but we're going to refeed it from underneath. I have to go on the catwalks and sea wall and jetties down below and fight off sea lions while running conduit 



wildleg said:


> what's the building going to be used for ? how far to land ? how deep is the water ?


It's a small two-story building. Just a rectangle basically; the bottom floor will be housing a big compressor and other equipment for their ammonia refrigerant system, the top floor is what you see in the pics, and is going to be purely electrical.

Solid land is about 100 feet away, actual dirt is about 200 feet away and across a street. The water is a bay, it's tidal, so it fluctuates from zero feet deep to several feet deep under the building. Don't tell me to go under there at low tide and drive ground rods :laughing:


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## RePhase277 (Feb 5, 2008)

Yeah.... I think running a GEC that far probably introduces more potential hazard than omitting it altogether.

In this one teens intseey lil' case, I might overlook it...:whistling2:


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## erics37 (May 7, 2009)

InPhase277 said:


> Yeah.... I think running a GEC that far probably introduces more potential hazard than omitting it altogether.
> 
> In this one teens intseey lil' case, I might overlook it...:whistling2:


Well I know that the inspector will never see it whether it's there or not, he's an 80 year old guy that won't go up stairs or ladders. But I'd like to install it if possible.... but it's hard to ground things when your structure is floating above the ground :laughing:


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## wildleg (Apr 12, 2009)

I think you're gonna be going for a swim


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## erics37 (May 7, 2009)

wildleg said:


> I think you're gonna be going for a swim


You mean my apprentice will be.


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## tates1882 (Sep 3, 2010)

erics37 said:


> You mean my apprentice will be.


Wheres the main grounded to? I would probably pull a ground in with the primary and "back bond" to the primary's panel. Not the best solution but better then a floating ground.


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## erics37 (May 7, 2009)

tates1882 said:


> Wheres the main grounded to? I would probably pull a ground in with the primary and "back bond" to the primary's panel. Not the best solution but better then a floating ground.


Might just wind up doing that.... Primary feeder is an aerial cable coming from the main building nearby but like I said, we will be installing new conduit & feeder from underneath. I'll be heading out there tomorrow, I'll dig around a bit more before I fall back to desperate measures. I might find some structural steel suitable as an electrode, if I'm lucky :thumbup:


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## Jlarson (Jun 28, 2009)

Bucket of dirt on the roof outside with a rod in it :yes: :laughing:

I'd too wait to see what you find when you go poking around, maybe there is something you can hook too. Sometimes you get lucky.


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## nolabama (Oct 3, 2007)

Back bonding. Never heard that one. Sounds ok tho. We bond structures over water to the water. But they are steel structures. If your fighting sea lions to run a conductor down the piling well I don't know if that's such a good idea. If no sea lions get a small boat and get a couple screw together ground rods and get em in


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## BBQ (Nov 16, 2010)

You have to do what it takes as far as it is. 

We have done a lot of work in old mill buildings and having to run the GEC down five floors is not unusual.


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## chicken steve (Mar 22, 2011)

Eric, your Q might rate here>


*ANSWERS:* Answers are the author’s opinions and do not represent formal interpretations of the National Electrical Code. 

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## BBQ (Nov 16, 2010)

chicken steve said:


> Eric, your Q might rate here>


What question? 

There is no wiggle room, if Eric (or his boss) wants to comply with the NEC he must get a grounding electrode connected to the SDS. 

There are no 'if it is difficult or costly' exceptions. :no:


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## erics37 (May 7, 2009)

BBQ said:


> What question?
> 
> There is no wiggle room, if Eric (or his boss) wants to comply with the NEC he must get a grounding electrode connected to the SDS.
> 
> There are no 'if it is difficult or costly' exceptions. :no:


The question isn't so much "Do I have to?" it's more "How should I?". Granted, none of y'all have been onsite yourselves but nothing we can do about that.

Would trenching a ufer into the pier slab be compliant?


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## Pete m. (Nov 19, 2011)

erics37 said:


> The question isn't so much "Do I have to?" it's more "How should I?". Granted, none of y'all have been onsite yourselves but nothing we can do about that.
> 
> Would trenching a ufer into the pier slab be compliant?


If there were no other options that may be as close to compliance as you can get. Not very familiar with marine type installations but is there a product available to "ground" to the water?

Either way it sounds like an application of 90.4 and would require "special permission" from the AHJ.

Pete


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## Bbsound (Dec 16, 2011)

I still don't see what's wrong with a ground ring. 

As far as back bonding I see this in 250.30
Exception No. 2:**Where a separately derived system originates in listed equipment suitable as service equipment, the grounding electrode conductor from the service or feeder equipment to the grounding electrode shall be permitted as the grounding electrode conductor for the separately derived system, provided the grounding electrode conductor is of sufficient size for the separately derived system. Where the equipment grounding bus internal to the equipment is not smaller than the required grounding electrode conductor for the separately derived system, the grounding electrode connection for the separately derived system shall be permitted to be made to the bus. *


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## nolabama (Oct 3, 2007)

You can use this http://www.nationalresistors.net
It's a resistor ground. I do not know if the ufer on the slab is compliant. It would not result in a " good ground" IMHO. I re read your op and edited this. 

Question. The only path to ground this place has is with Poco? Is no GEC present anywhere? 

I would bond to slab and bond to water.


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## erics37 (May 7, 2009)

UPDATE:

Okay I scoped out the job more thoroughly today. The existing transformer isn't grounded to anything. However, down underneath the building I found the metal water main coming in from the city. It's only about a 50 foot run to get to within 5' of where it pokes out of the ground so that pretty much solves all the issues. I just need to scrape all the rust off the pipe :laughing: Plus I have to navigate some sketchy looking scaffold planks between the pilings over the water. Whee!

But that's what I'm gonna hook my SDS up to :thumbup:

In regards to water bonding, I believe there is a grounding device that is basically a heavy ground plate that you attach a wire to and then throw in the water. Kind of like an anchor. It just sits on the bottom and settles into the muck. I haven't used one though, so I could be wrong.


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## chicken steve (Mar 22, 2011)

makes one wonder if UL has anything to do with anchors Eric....~CS~


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## RePhase277 (Feb 5, 2008)

erics37 said:


> UPDATE:
> 
> Okay I scoped out the job more thoroughly today. The existing transformer isn't grounded to anything. However, down underneath the building I found the metal water main coming in from the city. It's only about a 50 foot run to get to within 5' of where it pokes out of the ground so that pretty much solves all the issues. I just need to scrape all the rust off the pipe :laughing: Plus I have to navigate some sketchy looking scaffold planks between the pilings over the water. Whee!
> 
> ...


In this commercial/industrial setting, you can tie the GEC to the water line anywhere you want. It doesn't have to be within 5 feet. That is pretty much only a residential setting.


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## erics37 (May 7, 2009)

InPhase277 said:


> In this commercial/industrial setting, you can tie the GEC to the water line anywhere you want. It doesn't have to be within 5 feet. That is pretty much only a residential setting.


Interesting, didn't realize that I guess!

I think I'm going to run it close to the point of emergence from underground anyway, simply because they like to hack into water pipes a lot at this place :whistling2:


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