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I have to upgrade the service I have for an exterior building. The wiring follows the old code, and I'll need a permit to do it.

So I am going to have to update the service and everything to the newest code regulations, but have a little confusion on the bonding of the ground and neutrals.

Typically you bond the ground and neutral at the first cut off point after the meter, be that a panel or a disconnect.

But the meter and disconnect sit on one building, and the panel and grounding system sit at another building, with about 115feet of distance between them.

From what I understand, in theory, the area that you bond, should also be the entry point for the grounding. (I could be wrong about this though)

Aka my ground should initially enter my disconnect, then bond, then travel the 115 ft to my panel.

But since the grounding point is at the panel, I am not sure how to handle this.

I am not sure if I need to bring my ground wire, straight to the disconnect, then back to the panel.

Or Install a new ground bar at the disconnect, just to do the bonding and then tie the other ground system into it at the disconnect

Or do it as I have illustrated in the drawing attached

(which I believe might be the correct way of handling this)

which is:

bring the ground into the panel

tie it to the ground bar only

push it back through the conduit to the disconnect and bond it with the neutral there.

Am I correct in this? or am I missing something? enter image description here

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  • if you have a permit then you also have an inspector to keep happy. ask him/her directly to ensure the anonymous guy on the internet was correct with his advice.
    – ratchet freak
    Apr 11, 2019 at 15:52
  • I agree, however, I haven't been assigned anyone yet. And either way, I am certainly going to verify the answer, but I am hoping that whoever provides an answer, cites why they believe it is correct. As it will help with deciphering the logic behind it. Either way, you are right, I need to measure twice so to speak. But some external input will help put my mind at ease when I bring it up later on
    – Christopher Ortiz
    Apr 11, 2019 at 15:55

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You need a ground wire and ground rods at both structures

You are correct that you only bond neutral to ground at the service entrance. However, current Code not only calls for a grounding wire between the structures (which you have provided), but for a grounding electrode system at both buildings. This can be a concrete-encased electrode (if provided), or the old saw of two 8' ground rods driven 8' apart and connected with an appropriate-gauge wire if no better electrode (such as a concrete-encased electrode, foundation steel of some other sort, or a well casing) exists.

Each grounding electrode system gets a grounding electrode conductor back to the ground bar in the panel/disconnect for the associated structure, and the feeder equipment grounding conductor in the inter-building feeder connects the two together, from ground bar to ground bar.

You are also correct that the radio tower needs a ground rod, and that its ground needs to be bonded to the mains grounding system at the structure where the radio device (transmitter or receiver) is located. This ground wire goes to a tap on the structure's grounding electrode conductor, made using an intersystem bonding termination device or suitable tap connector.

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  • I believe you are correct in this. I was under the impression I would need to hunt down the grounding system and/or install a new one at the service entrance. (I was hoping not) After a little research, it seems like you are correct and this is indeed code. It requires separate buildings to each have their own grounding system. It also seems that if you use pvc and if you have nothing that is considered a metallic connection (which includes data, water, etc). you can run everything but ground, but you still need a GEC and in this case you need to re-bond, either way both ends need a GEC
    – Christopher Ortiz
    Apr 12, 2019 at 16:00
  • @ChristopherOrtiz -- no, the exception you are referring to is only valid for existing installation, not new work. IOW: you must run the ground wire between the structures for a new feeder, no exceptions any longer
    – ThreePhaseEel
    Apr 12, 2019 at 22:13
  • Ah, I seemed to miss that part. But for the sake of being informed on the original question, this is indeed an existing install, tower and all, just a 100 to 200 amp service upgrade using existing piping etc. Only changing a the disconnect, panel, and adding two 50amp outlets that are not illustrated.
    – Christopher Ortiz
    Apr 13, 2019 at 2:00
  • And in addition, just in-case it is relevant to the original question. This service upgrade is a dedicated meter that goes straight to the secondary building in the illustration, only thing it touches on the first building is a disconnect. I dont believe it changes anything, better to mention it than not. Also the tower is decommissioned, but I believe the grounding system still exists for it and hooks into the original panel. The original installation has a similar disconnect (fused however.. I was going to go non fused on this install) but that original disconnect had no ground/bonding
    – Christopher Ortiz
    Apr 13, 2019 at 2:03
  • I assume it was just done a long time ago and the code was different then o.0. It is rather old, and was a functioning radio tower. now its used (or will be used) as a Kiln room, for curing pottery. Hence the added 50 amp outlets and service upgrade to handle them along with an old A/c unit that is already installed. It is an old fire station with the old communications room (hence the big radio tower). Somebody decided to turn it into a learning center, and wants to fire pottery in the old comms room. I appreciate the feed back btw!
    – Christopher Ortiz
    Apr 13, 2019 at 2:09

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