Water Pipe Bonding

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bphgravity

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What is the purpose of water pipe bonding?

If it is to meet the requirements of either 250.4(A)(3) or (4), then why must the bonding jumper be sized per 250.66 and run to the service equipment and/or grounding electrode system.

Other piping systems do not have this stringent of a requirement. Based on the wording, a 200A home could have only 2 ground rods connected by #6 as the grounding electrode system and then have a #4 water bond? Doesn't make much sense to me.
 
Re: Water Pipe Bonding

I first thought this was an easy question. The water pipe is a grounding electrode, and the GEC is to be sized per 250.66. Case closed. I would not question having a GEC to a water pipe being larger than a GEC to a ground rod. I would have asked the question from the other direction. My question would have been more along the lines of "why is it OK to have a smaller GEC, when you are connecting to a ground rod?"

Then I took a closer look at 250 (a dangerous task, as we all know). I am now confused by something entirely different. 250.104(A)(1) says, in part, "The metal water piping system shall be bonded to (some things) OR to . . . grounding electrodes." Wait a minute. I though the water pipes were a grounding electrode. :confused:

So we must be talking about water systems that do not connect directly to the incoming water supply. Drain lines and "grey water" lines, perhaps? So I have to ask, not having done this type of thing before: Do you bond all water lines? In every room? On every floor? If you see a pipe, should you see a wire also? Or if you bond once, on the first floor, do you not have to bond anywhere else? What is the actual practice? :confused: :confused:
 
Re: Water Pipe Bonding

What I have are two houses that have internal water lines of copper that connects to a PVC pipe from the utility. Some of the water pipe is underground, some is through the attic space. All of the pipe is interconnected back to the house supply.

So we are not talking about water pipe that can be accepted as a grounding electrode, but still, the bonding of this pipe is treated as such.
 
Re: Water Pipe Bonding

If you look at the commentary the 2005 NEC Handbook the requirement of 250.104 can be better understood. The commentary is as follows:
Bonding the metal water piping system of a building or structure is not the same as using the metal water piping system as a grounding electrode. Bonding to the grounding electrode system places the bonded components at the same voltage level. For example, a current of 2000 amperes across 25 ft of 6 AWG copper conductor produces a voltage differential of approximately 26 volts. Sections 250.104(A)(1) and 250.104(A)(3) require the metal water piping system of a building or structure to be bonded to the service equipment or grounding electrode conductor or, where supplied by a feeder or branch circuit, to the building or structure disconnecting means or grounding electrode conductor. Information concerning bonding provisions for buildings with multiple occupancies and isolated metal water piping systems is contained in the commentary for 250.104(A)(2).
In those cases where it cannot be reasonably concluded that the hot and cold water pipes are reliably bonded through mechanical connections, an electrical bonding jumper is required to ensure that this connection is made. Some judgment must be exercised for each installation. The special installation requirements provided in 250.64(A), 250.64(B), and 250.64(E) also apply to the water piping bonding jumper.
 
Re: Water Pipe Bonding

Cripple, what would be the source energizing this interior piping system that would require a conductor sized by 250.66 to clear it?

Why can't we use a conductor sized by 250.122?
 
Re: Water Pipe Bonding

charlie b, the only reason that I bond to the water pipes is for safety reasons and it's the code. Accidential contact with a hot wire in the house would fault the circuit. Again I also bond to the duct system in the house.
Jim
 
Re: Water Pipe Bonding

Originally posted by bphgravity:
Based on the wording, a 200A home could have only 2 ground rods connected by #6 as the grounding electrode system and then have a #4 water bond?
Click to expand...
That's exactly what we do for a 200-amp service.


Originally posted by iwire:
Cripple, what would be the source energizing this interior piping system that would require a conductor sized by 250.66 to clear it?
Click to expand...
Apparently, the service itself, or perhaps (left over from all-metal water service systems) hot plumbing brought into the premesis from a pipe-fault nearby.

We must assume that code requirement have evolved over the years in an attempt to keep up with changing conditions and events, like stop signs and traffic lights.

We now know which intersections will require lights as we build them, but they had to be invented as a result of need, just like the NEC. We know about electrical fires and electrocution now, but not always.
 
Re: Water Pipe Bonding

So now I have a 400A service fed with 600-kcmil conductors. The grounding electrode is the concrete-encased rebar and is connected with the max required #4. There are no other electrodes present. This same structure has structural steel and interior metal water piping.

These now are both bonded with 1/0 copper to the same concrete encased electrode as required and permitted by 250.104(A)(1) and 250.104(C).

Can someone explain the logic of this?
 
Re: Water Pipe Bonding

look at 250.104 (A) (2), in a multiple occupancy
building, it can be sized in accordance with 250.122, so a single family home would have to have the water pipe bond sized in accordance with 250.66 but a multiple occupancy can be sized in accordance with 250.122, whats the difference.
 
Re: Water Pipe Bonding

Originally posted by tom baker:
Perhaps this is where you can use a sheet metal screw?
Click to expand...
That's exactly where I was going. I don't see that there is an exception to 250.8 for sheet metal screws to bond ductwork.
 
Re: Water Pipe Bonding

In the code book, where does it state a water pipe must be used as an electrode?

Dnk....
 
Re: Water Pipe Bonding

NEC 250.50

all grounding electrodes as described in 250.52(a)(1) through (a)(6) that are present @ each building or structure served shall be bonded together to form the grounding electrode system.

Where none of these electrode exist,one or more of the grounding electrodes specified in 250.52(a)(4)through (a)(7)shall be installed and used.
 
Re: Water Pipe Bonding

Dillon, take note that N.C. amended the 2005 wording of 250.50 and used the 2002 wording.

See page 9 of this document .


I wonder if any other States did the same?

Roger

[ September 09, 2005, 07:14 PM: Message edited by: roger ]
 
Re: Water Pipe Bonding

No Roger,

I hadn't seen that.. Thanks for bringing that to my attention. And you do raise a good question involving 250.52(A)(7)*and the underground metal well casings and has the other states, where adopted..

I have followed conversation in this forum, on this subject.

Edited:*need to read this again,missing something :confused:

Edited again: *All to IF? Roger,is this the change?

[ September 09, 2005, 07:47 PM: Message edited by: dillon3c ]
 
Re: Water Pipe Bonding

Dillon, one thing the change in the 05 NEC wording means is, if there is a concrete incased electrode in the slab it must be used even if (for the sake of conversation) it is not available. (Get out the chipping hammer)

I think N.C. recognized this, and decided the 02 requirement of "if available" was sufficient.

Roger
 
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