Bonding a metal water piping system where there are multiple service disconnects

[rojay]

I don’t know if this has come up before, but does the NEC give guidance on how to complete the bonding of a metal water piping system when there are multiple service disconnects involved?

For simplicity, let’s say this pertains to a house with copper water piping throughout, but the underground supply portion of the piping is plastic. The underground water piping does not qualify as a GEC, but the bonding requirement of NEC 250.104(A) is still in play.

If the home has a 400 amp service with two 200 amp MCB panels as disconnecting means, how is the bonding to be completed? My first thought is that this would be treated the same way a grounding electrode system w/ multiple service disconnects is per NEC 250.64(D). The trouble with that thought is that it seems to conflict with the bonding jumper installation instructions in 250.104(A).

Does anyone have thoughts on this? Is it sufficient to bond to one service disconnect enclosure?

 

[jaggedben]

I don't see a conflict with 250.64(D) like you're saying. 250.104 doesn't say you can't do it like 250.64(D) says, it just doesn't say you have to. I think if you do it like that, just using the other table for sizes, you're fine. But that's not required.

Going by the letter of the code, it does seem sufficient to bond to any one of the service disconnect enclosures. (That is, if the water for all units is metallicly connected and 250.104(2) does not apply.) Personally, if feasible, it seems to me more prudent and sensible to bond it to the neutral upstream, or to the common GEC or electrode. But that's not required.

 

[Buck Parrish]

I agree with jaggedben . And even If the grounding electrode wire happen to be running near by. You would be able to attach to that.

 

[rojay]

I don't see a conflict with 250.64(D) like you're saying. 250.104 doesn't say you can't do it like 250.64(D) says, it just doesn't say you have to. I think if you do it like that, just using the other table for sizes, you're fine. But that's not required.

Going by the letter of the code, it does seem sufficient to bond to any one of the service disconnect enclosures. (That is, if the water for all units is metallicly connected and 250.104(2) does not apply.) Personally, if feasible, it seems to me more prudent and sensible to bond it to the neutral upstream, or to the common GEC or electrode. But that's not required.

I think you‘re right, I may be misreading 250.104(A). The fact that it calls out 250.64(A),(B), and (E) as bonding jumper installation instructions is really just saying to treat it like a GEC (with the exception being that it doesn’t need to be continuous).

It sounds like any of the three options in 250.64(D) would be the way to go in this situation.