Multiple waters pipes in multi-family buidling

[rlane00]

We have a 12-unit multi-family building with a single 800 amp service (ganged meters) and three separate metal water pipes stubbed up into the building. One pipe is for the sprinkler system and the other two are for the 12 units, but are converted to plastic within a few feet of stubbing up from the floor and distributed to each unit from there.

My question is how to run GEC and/or bonding. Per 250.66 I need 3/0 copper for the GEC, but I'm not sure if I need to run this to all three of the water pipes, or to just one (the closest to the service) and then bond the other two. Based on 250.104(A)2 it appears that I can just bond the other two (using #8 since each unit has 100 amp OCPD) to the panelboard for that occupancy - but the water pipes are not supplying a single occupancy so I'm not sure if this section applies.

I searched this site and found a similar thread http://forums.mikeholt.com/showthread.php?t=79699&highlight=multiple+water+pipe from 2006, but would appreciate some current feedback. Thanks.

 

[bphgravity]

Based on my interpretation of 250.50, both underground metal water pipes must be bonded together to form the grounding electrode system. The sprikler pipe is PROHIBITED from being used as a grounding electrode per the NFPA 13.

Based on your description 250.104(A)(2) does not apply.

Unfortunately, it is likely you will have to install a full sized GEC to the first water pipe, or both, and/or bond the second water pipe via a bonding jumper sized the same as the GEC. If determined by the AHJ, you may be required to bond the interior portion of the sprinkler piping in compliance with 250.104.

 

[rlane00]

Thanks for the quick response. Unfortunately I do not have a copy of NFPA 13 but did a little research and found the following article on the subject http://www.mail-archive.com/sprinklernotes@firesprinkler.org/msg00037.html which supports your statement.

I checked with the AHJ and he was not familar with the NFPA 13 prohibition. He did state that NEC does not differentiate between domestic and sprinkler water and therefore the sprinkler pipe must be bonded together as well. I asked which of these contradictory requirements take precedence... and he is looking into it.

For what its worth, we have been running a GEC to the sprinkler pipe 100% of the time at the other buildings in this complex and all have passed inspection.

 

[G0049]

Is the sprinkler pipe you mentioned a pipe going out to the sprinkler system, or a separate supply from the main that will feed the sprinkler system? If its a separate supply coming in from the main, it should be treated like any other supply pipe.

 

[rlane00]

I believe that the sprinkler pipe is a separate supply coming in from the main, but I'd have to check with the sprinkler guy to make sure. I did speak with the sprinkler guy yesterday and he confirmed there is more than 10' of metal in contact with earth - but he said he never sees any electrical connection to his pipe.