Multiple occupancies bonding

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Pierre C Belarge

Pierre C Belarge

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Westchester County, New York
If we have a situation where there are multiple occupancies in one building with a service supplying the building having one main service disconnect. The occupancies are then supplied with feeders, each having an EGC installed to the occupancy. The building is built in such a way, that each occupancy has it's own metallic water supply and meter, the metallic water pipe does not go through the building, but is supplied to each occupancy from the outside city supply via an underground installation.

Can I use 250.104(A)(2) for my installation? Do we need the plumber to install a nonmetallic isolation section to these units?
 
This is a condo group where the utility company required the EC to have all of the meters in one location outside the building. It is one building, but there are fire walls and 8 different units. They all have there own water supply. Can I use 250.104(A)(2)? I notice it says "metallically isolated" by use of "nonmetallic water piping"...
This would change the table(s) for reference - 250.122 or 250.66.
 
For a new installation, the article you mentioned looks to me like the specific method to satisfy a fire inspector expecting 6 disconnects, whether there are fire walls or not.

Assuming 250.104(A)(2) is used, that article does not mention isolating the cold water pipe ground so it appears to be a design issue. It is good design practice. There may end up being stray currents, utility questions about corrosion, etc. 250.6(B)(3) seems to permits the isolation for:
Breaking ground loop
Single point grounding
 
Pierre, this is similar to a question I had last year, in this thread.

I think your mental approach to the predicament is from an opposite angle than I would take. Since each of your pipes qualify as grounding electrodes, we have to start in Part II and III of 250, and work forward from there. If we're using the grounding requirements, then the bonding requirements in 250.104 will likely be taken care of before we even get there.

There's different ways of looking at this:
  • We have one building. There are eight 250.52(A)(1) grounding electrodes present that require us to use them as grounding electrodes by 250.50. So all eight are connected to the service.
That one's fairly straightforward.

Or:

  • We have eight buildings. One is supplied by a service, the others by feeders from the originating "structure."
  • Each detached structure would fall under 250.32, and we'd install a MDP (per Art. 225) and run a GEC from each unit's main disconnect to the grounding electrode(s) present in each unit.
  • Each unit would need a supplementary electrode for the .52(A)(1) one.

That one is a headache to think about. But you can see where I'm going with it - 250.104 doesn't really come into play unless the piping is non-metallic underground to start with. You seem to indicate it's metallic, but I could be mistaken. :D

Edit for clarity
 
Pierre,If there is a main disconnect for the building,then there should be a gec to the cold water supply already.If there are seperate water meters for each occupancy,there should be a bonding jumper across each water meter.If the entire water supply to each occupancy is metallic, then seperate bonding jumpers are not required from each occupancies panel because there is a main disconnect.If they were isolated with plastic then 104(A)2 says that you can use the egc in the feeder to bond to each occupancy's seperate metal water supply.If the main water supply is totally isolated where even the main disconnect gec is not attached to it,then it should have failed inspection.
Rick
 
Okay, the question is not as easily answered as was suspected.

There are 8 units.

There is a main supplying the meterbank.

The 8 units are supplied by feeders from the meterbank

The 8 units have their own water supply/meter, with the water entering the different units separately (the water pipes enter each unit without traveling through another unit)


Can the bonding be done, applying 250.104(A)(2), table 250.122 or do I use table 250.66 as per .104(A)?
 
The Grounding electrode conductor is for the disconnect - Service entrance conductors. Feeder to each unit is not service entrance.

The service entrance/disconnects are grounded using 250.66

The condos, whether or not they have individual water service, metal or plastic water lines, whether or not the water meters are removed, have their metal water systems bonded into their feeder panel using 260.166. The feeder panel is bonded to the disconnect using 250.166. The feeder OCD and Table 250.122 is used to size both these EGCs.

Sorry if it takes forever to look at the picture (2002 Handbook ex. 250.46). The text was illegible at 50%...

 
Pierre C Belarge said:
Can the bonding be done, applying 250.104(A)(2), table 250.122 or do I use table 250.66 as per .104(A)?
Click to expand...
Consider this picture:



Notice the points on the water system where I drew triangles with cherries in them.

If you install plastic from outside the building to inside, then IMO you may size bonding jumpers from the panelboards to the interior water pipes per 250.104(A)(2).

If you have continuous metallic piping running from inside to outside, and that pipe is 10' long, (which it is), then I say you must install jumpers between each point, treating each unit's water service as a grounding electrode (per 250.50 & 250.52(A)(1)). It would be easiest to consider the eight units one structure for this.

That way, you install one GEC to the nearest water pipe to the service, and then bonding jumpers to each successive water pipe entrance to the building after that.

IMO.

Edit for reference and to add "IMO."
 
Pierre

I don't see any info on the water system before it enters the building.
If each water service goes underground and then changes to plastic, then you could bond to each subpanel.
If it is metal below ground as well, then one connection is required(the above would not be permitted) and you have a water pipe which qualifies as a grounding electrode.
Don't forget jumpers around any water meters, etc.
 
I ran into a very simular situation not to long ago 12 12 unit condo with 2 seperate mains and grouped meters and mbrs that were piped thru the slabs into each unit.each unit was CU piping and isolated from eacother.The inspector had us run our ground wire sized to 250.66 from the 600 a main to the neatrest cu pipe after hitting building steel.We then went from each units 125 a panel in the mechanical room with #4 bare to the cold water side of piping entering for the water heater in that unit also in the same mech room.Could have used # 6 but we had 3 rolls of # 4 0n the job.As I read the code as long as they are (the water systems ) are isolated from one another it is permissable to hit the water pipe in thos units and as long as terminations are accesable it is acceptable.We passed 144 units this way.
 
allenwayne said:
Ours had pvc to the meter that was in a hand hole and from there it was CU
Click to expand...

That's similar to what our water district does.

We typically only have 3 to 5 feet of copper in the ground. Only every once in a great while does a water line qualify as an electrode here.
 
Thank you for making that clear Larry. Found an article about this here.

This statement is wrong:
The condos, whether or not they have individual water service, metal or plastic water lines, whether or not the water meters are removed, have their metal water systems bonded into their feeder panel using 260.166.
Click to expand...

Obviously I had several typos referencing 250.166(??) The point was that that separate metallic water systems in the units will by itself allow using a smaller (250.122) bond, is not what is said in the code. What I don't know is why now I stop trying to admonish those wiser than myself.


Pierre "shall" bond the feeder using 250.104 (A), (B), (C,) "or" (D). To use 250.104(B) to size the feeder bond using 260.122 requires that there be mechanical isolation "by use of nonmetallic water piping," for my 2002 handbook. The Mike Holt article, based on the 2005 NEC, says, "If the metal water piping systems in individual occupancies do not mechanically connect to each other."
 
Peteo
I am not discussing service grounding in this thread.

I think that you guys are understanding what I am asking. The main question is: I do not have any isolated water pipes (or as I understand what the NEC is saying is isolated), I have continuous water pipes. Now, can I use 250.104(A)(2)?
 
I would say no, 250.104 (A) (2) states mechanically isolated in its verbiage but I think it would be a good idea anyway in case the system ever became mechanically isolated which is entirely possible.
 
Pierre C Belarge said:
I do not have any isolated water pipes (or as I understand what the NEC is saying is isolated), I have continuous water pipes. Now, can I use 250.104(A)(2)?
Click to expand...

Pierre
You can't.
You fall under 250.104(A)(3)

My point previously and I think confirmed now, is that you must have a water pipe that qualifies as a Grounding Electrode.
If those metal lines are not isolated from each other, then they must connect together ouside the bldg underground. I can't see how you would not have 10 feet of metal water pipe in the ground
 
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