dielectric union

Where are dielectric unions used besides water heaters?

Ar they required on all water heaters?

A dielectric union is designed to break the electrical contact between two dissimilar metals (to prevent galvanic corrosion). Most of the flexible copper connector hoses on water heaters have a plastic washer that acts as a dielectric union.

Dielectric unions are used anyplace where a copper pipe connects to a galvanized steel pipe.

You should not need it if you don’t have dissimilar metals, especially galvanized steel to copper contact.

If a flexible copper connector is used is it reasonable to assume the washer cannot be seen during a home inspection?

Texas is redoing their SoP and have this new requirement.

Visual inspection means just that.
If you were unscrewing plumbing to check for missing parts , you, would have worse problems than lack of a proper dielectric union.

You can typically see part of the plastic washer/flange sticking out at the top of the fitting.
This plastic fitting is frequently damaged when the fitting is tightened too much, causing a loss of the dielectric properties.

It would be difficult to verify the integrity of the washer/flange.


If there is a problem it will eventualy corrode.
Might as well watch the grass grow.

Ya I thought of that. Seems like the water heater would fail before serious dielectric corrosion. They only last 6 to 10 years here.

Problem is if Texas puts it in the SoP I have to work with or around the requirement.


I hear ya.
All you can do is your best.
Kinda like how in Illinois we observe the plumbing which is worded differently from the other systems that we are required to inspect.
Everyone says it is because of the plumbing union , but my opinion is it also has to do with not unscrewing and turning shutoff’s.
Plumbing is like that as we all know.

Good Picture :slight_smile:

dialectric union.JPG

The corroded, leaking dielectric union in the back was installed by a ‘licenced plumber’. I installed the copper tube/hose and fittings. I paid quite a bit more for the brass fittings, I guess that is why people like the galvanized steel ones (cheap).

Check out these steam pipes connected with galvanized metal fittings.




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IMO Dielectric unions have very limited benefit as the water within the pipe also conducts current, effectively defeating the “isolation” provided by the dielectric device. I see corroded nipples and fittings on and around water heaters all the time, regardless of whether dielectric isolated unions, couplings, connectors, etc. are used. Sometimes it’s caused by the copper flex connector with the integral isolator itself. Brass seems to have more universal compatibility, which is why I prefer to see brass nipples.

I’ve attached and old tech bulleting from Rheem on the topic. I’m not sure if it’s still accessible on their site. Also note that the nipples on top of the water heater are supposed to be dielectric, but as far as I know you can’t tell visually once the plumbing is hooked up.

Probably better for the TX SOP to call out actual corrosion rather than all of the dielectric / non-dielectric scenarios or we’ll wind up with another SOP standard as silly and confusing to the public as the no AFCI defects in older homes.

********** PDF too big to attach - here’s the text - sorry for format *****
Published by Rheem / RUUD

OK…What exactly are they saying? Are Dyelectric fittings needed or not?

The way I read it is that Dyelectric fittings are not to be used becase the SAME type of pipe is required throughout. Correct?


Here is what happens when they are not used. Home was built in 2007

I did not look at the picture on your post earlier. the nipple on the cold water connection in the photo is shipped by the water heater mfg that are delivered to plumbing suppliers and are used to prevent a galvanic reaction. Because the fittings add about $5.00 to the cost of the heater retail stores such as Home depot buy their heaters with out the nipples. Most of the problems occur when water heaters are installed by homeowners that do not know any better or by the plumber that works out of the back of his truck