ECN Forum Forums Code Related Discussion NEC & other Code issues Bonding of water piping.

How do you handle the bonding of a water piping system that is made up of dissimilar metallic piping and contains one or more dielectric unions. If you bond the various segments of dissimilar metallic piping to each other you will have shunted out the dialectic union thus assuring the galvanic action and resultant corrosion that the dialectic unions were installed to prevent.
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Tom H

Tom- I guess this issue has been around as long as I can remember. I would like to comment that if the piping is to be continuous electrically, I would expect to see a jumper for example between the H and C water pipes so the dielectric unions don't isolate a part of the piping system that may become energized and cause an electrucal hazard. I'm sorry, Mr. Plumber, but the law says I must do this. Now for the real world. I don't think there are 5% of the electrical inspectors out there that check this item out and enforce this item. There are so many more items that are not jumped around to maintain continunity that the dielectric union is not even addressed by the electrician. Then we have the non metallic piping and isolated metal plumbing fittings and faucets. In fact since the code has evolved to where the GEC is only permitted to be connected to the water pipe electrode within 5' of where the it enters the building, the only thing that gets inspected for this issue is the water meter and any water filters or water softeners located at the water service entry. Am I off base with this? Good question might be does the plumbing code require dielectric unions? or Does the plumber only install them to prevent the galvanic action?

Tom
That is a good question, one that I believe someday we will have a proper answer. As for now, the NEC requires this and we will install accordingly. This topic will create "lively" discussions on the job and this site for sometime to come .

Pierre

I think the "gas pipe" standard is most applicable. The pipe should be bonded to the EGC of the circuit most likely to energize it. If you have line powered equipment on isolates sections of metal pipe you should bond to the EGC.

I think we're confused as to what a dielectric union does. It only prevents corrosion at the point of contact, by insulating the one piece from another.
Were you to install a bonding jumper, this would not "defeat" the dielectric union at all. Any corrosion, caused by the connection of different metals, would be at the site of you jumper connections. Since our connectors are usually of copper or zinc plated steel, rather than bare steel, galvanic corrosion should not be an issue.

I agree John, I would further say that the current created by dissimilar metals in contact require that they be in contact. The terminals used for a jumper ,I would hope, wouldn't have the same reaction.

I cant guarantee that I used valid technique but a hall effect clamp on ammeter measured a small current in the water heater jumper were the supply to the water heater was galvanized iron pipe and the hot water line was copper. I turned off the main breaker and lifted the neutral to separate the home from the outside world and the reading of a few milliamperes of DC current did not go away.
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Tom Horne

George,

I look for the bonding jumper on the water heaters and I look for plastic water softners, and plastic water filters. Most times people forget to throw a bonding jumper on thoses pieces of equipment. I once saw a house that kept getting "pin hole" leaks in the house. Long story short, there was a plastic water filter and once there was a jumper on it, no more pinhole leaks. That was more than 5 years ago.

Harold,

I can't let you get away with that.

You're going to have to bring more to the plate, or, at least I, will discount the assertion.

Hi,
This subject just came up on a job I am doing. The plumber said that he was not going to be responsible for what my bonding does to his copper lines. He was surpirsed that I was going to bond the spa pump to the cold water copper supply line. He said that his code did not allow this.

I told him that I was going to bond ACROSS the HW heater too and he said he would disconnect it.

This job has a plastic line coming in that switches to copper. I put in two ground rods and ran a #4 to the HW heater to bond across the piping there. Does the 5 foot rule still apply or am I ok at the HW heater?

Apparently the HW heater is the problem. The unit insulates the hot and cold.

-regards

Greg