205.104 - water piping with dielectric fittings

[rodroche]

I need some advise on an inspector's question on grounding/bonding of metallic water piping systems. The plumber used both stainless steel and copper piping for the domestic water system. He installed dielectric fittings between the two types of pipe. Now there is an electrical question about how to meet 250.104, as now the copper sections are isolated from the stainless steel. The 6" main is stainless, then changes to steel as it exits the building (underground). Installing a bonding jumper across the dielectric fittings seems to defeat the purpose of the dielectric fitting. Should I bond all the isolated copper sections together and then use and bond there to the main line? Any help would be appreciated.

 

[charlie b]

I asked the lead plumbing engineer in our office. He said that a bond wire across the dielectric fitting would not create a problem. He said that the danger of galvanic corrosion is entirely related to what happens within the water. Two dissimilar metals in close proximity, with water flowing through both, will create a galvanic cell. Separating the two metals by sufficient distance will eliminate the galvanic cell. It is the distance that does the trick, and that is the purpose of the dielectric fitting. He said that the galvanic action takes place entirely within the fluid, and therefore an external bond wire would have no adverse impact.

Please note that I am only reporting what I was told by someone I work with, someone whose judgment I trust. But don?t rely on that alone. It?s a start, but I would be happy to have someone else confirm (or refute) this statement.

By the way, did you ever live in the Seattle area? :-? I once worked with someone with the same name.

 

[rodroche]

Thanks Charlie. How many guys you know named Rod Roche? Yes I am the same guy. I moved to Colorado two years ago, and am very happy. Thanks for the post. My plumbing counterpart had the same idea. We will put it to the electrical inspector. email me sometime.

(I'll do that, Rod. But we don't like to show email addresses in the public area. It's a privacy thing.)

 

[George Stolz]

This topic's come up quite a bit lately, in various aspects.

I am replying to your PM publicly, as it's best to let everyone have the chance to shoot something down if I am wrong:

We have a water piping system with several dielectric fittings. Can I place a bond across this fitting to make it electrically continuous? If I can, what size does the jumper have to be. I size the GEC at 3/0 as we have a very large service. However the main piping is stainless steel, and at the dielectric fittings changes to copper. The inspector red tagged it, as there were parts of the metal water piping system that were not bonded.

I would say that if the inspector (acting under the opinion of the AHJ) views the metal water piping after the dielectric fitting as covered under 250.104(A), then the conductor must be sized according to Table 250.66, which would be the same as your 3/0 GEC, IMO.

Bear in mind, there is disagreement as to whether what the inspector is requiring of you is required by the NEC - there are panel statements to refute it.

If you'd like to look over the FAQ on this topic, click here.