ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
Recent Posts
Al Hildenbrand - Minneapolis - obituary
by bcpappas - 02/02/23 08:01 PM
by renosteinke - 01/27/23 09:52 PM
Does NEC 551.71 (F) apply to dwellings?
by BigB - 01/20/23 10:46 AM
Power submeter connections
by HotLine1 - 01/19/23 09:09 AM
New in the Gallery:
Burger King crown sillyness
Burger King crown sillyness
by wa2ise, December 11
240/208 to a house
240/208 to a house
by wa2ise, October 9
Who's Online Now
0 members (), 23 guests, and 14 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
#169216 09/28/07 10:51 PM
Joined: Jul 2007
Posts: 1,335
I would like to throw this out to you all. An issue I keep running into is what size bonding wire to use to bond the hot water pipes and the cold water pipes at the water heater. This can apply to other equipment such as water filters, softeners, and other similar equipment. I have gotten many different answers however there is only one in my code book. Here is the scenario:

You are wiring an 8 unit apartment building. The service is an 800 amps fed with a lateral service of 2 sets of 500mcm cables from the utility’s transformer to the building’s 800 amp disconnect. The disconnect feeds a meter stack that holds a meter and a 125 amp breaker for each unit. Each of those breakers feed a panel in each unit with a set of #2 wires and a #6 ground. The 800 amp service is grounded with a Ufer, a couple ground rods and a bare 2/0 going to the main water line.

The water system is supplied by a 4” steel water line from the city that is greter the 10 feet long. From there it is all copper throughout the building. Each unit is fed with a ¾” waterline that splits off to feed the cold water faucets and a line goes to feed the 4500 watt electric water heater. From the water heater, the hot water is then supplied throughout the unit to the hot water faucets. This is repeated in each unit so each unit has its own water heater and each water heater has dielectric fittings.

The questions:
1. Would you bond the hot and cold water lines together?
2. If so, what size of the bonding jumper would use to include the code reference?
3. If the dielectric fittings were not in the water heater, would you still bond the two together?

If this post looks familiar, I have posted this on other message boards. I feel that is an important area that is over looked and often misunderstood.

FYI the wire sizes are correct and they do meet code.

"Live Awesome!" - Kevin Carosa
Stay up to Code with the Latest NEC:

2020 NEC & Related Reference & Study Guides
2020 NEC & Related Reference & Study Guides
Pass Your Exam the FIRST TIME with these Exam Prep Combos:

>> Master Electrician Exam Prep     >> JourneyMan Electrician Exam Prep

Joined: Oct 2000
Posts: 2,722
Broom Pusher and
I would have to say, if "Supplimental Bonding" was required (supplimented by a Conductor, as the Hot & Cold are physically bonded at each mixing valve), it would be done for each unit - likely at the Water Heater its self, using a Conductor sized to the largest circuit value of that unit (largest OCPD in the unit's Panelboard).

If there may be issues where the Tenant's Feeder(s) could energize the Hot Water Pipes, then the Bonding Conductor would be sized according to the OCPD of the Tenant's Feeder.

This _SHOULD_ fall under article 250-122, like an Equipment Grounding Conductor.

Fire away!!! shocked


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!
Scott35 #169237 09/29/07 11:17 AM
Joined: Jul 2004
Posts: 9,788
Likes: 14
250.104(A)(1)The bonding jumper(s) shall be sized in accordance with Table 250.66 except as permitted in 250.104(A)(2) and (A)(3).

(2) ...the individual occupancies is metallically isolated from all other occupancies by use of nonmetallic water piping... 250.122

(3) ... 250.66 again

It sure sounds like 250.66 to me.

Greg Fretwell
Joined: Jan 2004
Posts: 1,507
Greg- You are 100% correct. IMHO 250.66 applies for system bonding and 250.122 applies for equipment bonding.

George Little
Joined: Jan 2003
Posts: 4,391
For water line bonding it's 250.66 although I do not know why it could not be 250.122

Bob Badger
Construction & Maintenance Electrician
iwire #169261 09/30/07 10:26 AM
Joined: Jul 2004
Posts: 9,788
Likes: 14
I do tend to agree with the concept of bonding based on the "circuit likely to energize" when you have isolated sections of any kind of pipe. You are still oblgated to use 250.66 for the general bonding of water pipe systems.

Greg Fretwell

Link Copied to Clipboard

Tools for Electricians
Tools for Electricians

* * * * * * *
2023 National Electrical Code (NEC)
2023 NEC Now Available!
* * * * * * *

2020 Master Electrician Exam Preparation Combos
2020 NEC Electrician
Exam Prep Combos:
Master / Journeyman


Member Spotlight
Leo, IN, USA
Posts: 28
Joined: June 2004
Top Posters(30 Days)
BigB 4
triple 3
Popular Topics(Views)
303,033 Are you busy
232,132 Re: Forum
216,843 Need opinion
Powered by UBB.threads™ PHP Forum Software 7.7.5