Bonding of Metal Water Piping

[iggy2]

250.104(A)(1) requires bonding of metal water piping installed in or on a structure, to one of several elements of the grounding system. No problem.

We have a multi-occupancy structure (apartment building) where the copper water mains are being replaced with CPVC mains, since the copper is springing leaks everywhere. This will metallically isolate the copper piping in the apartments, which will remain, from the existing bonding connection which is via the copper mains, as was required by 250.104(A)(1).

250.104(A)(2) addresses multiple occupancy buildings, and permits the bonding of the now-metallically isolated piping to the equipment grounding terminal of the switchgear, switchboard or panelboard supplying that occupancy.

Is the bonding of the metallic water piping in the apartments, now isolated by the CPVC water mains, required to be bonded to one the listed elements? Or does 250.104(A)(2) trump 250.104(A)(1) in this case of multiple occupancies with metallically isolated piping??? Is the bonding merely permitted, and NOT required?

 

[mtnelect]

If you have at least 10 feet of underground metallic water piping service to the structure, then it should be bounded to the service. See attachment.

 

[LarryFine]

Not what he's asking, which is: Now that the common sections of water pipe are being replaced with plastic, must each apartment's now-isolated metal piping be re-bonded.

I'd say yes. Unlike having small, isolated section like at single fixtures, each premises has a complete metallic system.

 

[mtnelect]

"Also, in buildings of multiple occupancy where the metal water piping system(s) installed in or attached to a building or structure for the individual occupancies is metallically isolated from all other occupancies by use of nonmetallic water piping, the metal water piping system(s) for each occupancy shall be permitted to be bonded to the equipment grounding terminal of the panelboard or switchboard enclosure (other than service equipment) supplying that occupancy. The bonding jumper shall be sized in accordance with Table 250.122, based on the rating the overcurrent protective device for the circuit supplying the occupancy".

 

[wwhitney]

250.104(A)(1) will apply to the metal water piping system(s) downstream of the new CPVC, and 250.104(A)(2) if it applies is just an additional option for compliance.

How extensive is the CPVC replacement? If it's just one long segment with no branches, then the apartments won't end up isolated from each other, and 250.104(A)(2) doesn't apply. Seems simple enough to install a single properly sized bonding jumper in parallel with the CPVC, connecting the the metal piping systems at each end of the CPVC.

If it's more extensive, then you will need a bonding jumper for each downstream isolated water piping system. These could follow the CPVC back upstream and connect up with each other as the CPVC does. How many apartments and how many isolated water piping systems?

Cheers, Wayne

 

[infinity]

Many apartment buildings have a separate water meter for each unit and therefore the piping between apartments is isolated except maybe for where it enters the building before it hits the meters.

 

[wwhitney]

Many apartment buildings have a separate water meter for each unit and therefore the piping between apartments is isolated except maybe for where it enters the building before it hits the meters.

But if the water piping is all metallic then you could just jump around each meter and treat it as one big system, right?

Cheers, Wayne

 

[augie47]

IMO, 250.104(A)(1) would require the individual systems to be bonded. (A)(2) simply provides you with an alternative method of bonding them in isolated multi-occupancies.

 

[iggy2]

After further review and discussion, I agree with augie. The piping has to be bonded, but (A)(2) just permits you to go to a distribution point closer to the dwelling unit. And size the bonding conductor per the feeder to that distribution. Which would have been nice.

In this case, each stub off the copper main feeds kitchens and baths of 4 dwelling units, so they will NOT be isolated. So (A)(2) does not apply in this case. We have to go back to the service equipment, or the GEC.

But the bigger issue now - there is a 1,200A service, so 1,500 kcmil total area of service conductors. Per Table 250.102(C)(1), the bonding conductor has to be 3/0. Sigh. How to connect 3/0 to 1/2" and 3/4" copper pipe stubs??? I'm sure there is a fitting, but I am more concerned about the 3/0 putting strain on the copper piping!

We have reached out to inspector of wires to see if he would accept a smaller bonding conductor IAW 90.4 para 2.....

 

[infinity]

there is a 1,200A service, so 1,500 kcmil total area of service conductors.

Just curious what size conductors?

 

[iggy2]

Just curious what size conductors?

(3) 500 kcmil per phase and N.

 

[infinity]

(3) 500 kcmil per phase and N.

Add that to your list of problems.
385*3=1155 amps

 

[augie47]

250/104(A)(3)) for multi-occupancy allows you to size the bonding jumper based on the feeder size so the 1200 amp service isn't relative for those individual occupancies.

The 3-500s might be another issue. (as infinity just noted)

 

[wwhitney]

250/104(A)(3)) for multi-occupancy allows you to size the bonding jumper based on the feeder size so the 1200 amp service isn't relative for those individual occupancies.

I read 250.104(A)(3) as only applying to multiple structures. So if it's all one apartment building, it wouldn't apply.

Cheers, Wayne

 

[iggy2]

Add that to your list of problems.
385*3=1155 amps

An existing condition....

 

[iggy2]

250/104(A)(3)) for multi-occupancy allows you to size the bonding jumper based on the feeder size so the 1200 amp service isn't relative for those individual occupancies.

(A)(3) applies to buildings served by feeder or branch circuit (like an outbuilding, or shed?). I don't think that applies here, since this building is fed by a service.

If we were to use (A)(3), it opens the question of which OCP device we would be talking about - the 1,200A main (right back to a 3/0 bonding conductor), or the 80A feeder circuit breaker at the meter stack feeding the dwelling unit loadcenter (in which case a #8 bonding conductor). I like the #8, but don't think we can say the building is fed by a feeder.

 

[Dennis Alwon]

All metal piping systems must be bonded. In this case it appears you do not have to bond it back at the service if you so choose but it must be bonded.

Question
1) Are there water meters for each unit?

If so then just bond based on T250.102(C)(1) and jump to each meter.

 

[iggy2]

1) Are there water meters for each unit?

Nope. One meter (with a jumper) at the water service entrance.

 

[Dennis Alwon]

So if the metal pipes are not connected then that jumper should suffice.

 

[iggy2]

The pipes are currently bonded, via the bonding jumper from the switchgear to the water meter. Once the copper pipe water mains in the building are replaced with CPVC, the water piping in the dwelling units will not longer be bonded. Hence having to add a (3/0) jumper along the CPVC piping, to bond all of the copper stubs running into the dwelling units.