I've done a bit of research on the subject. They say don't connect copper to
galvanized. Some sites say to use a dielectric union between then. Some say
brass can be used instead. I've seen dielectric unions with a hard copper wire
connected to both pipes - seems like that would defeat the purpose of the union,
but does code require it?
I currently have galvanized pipes with galvanized pipe coming into the house,
and am planning to replace the inside pipes with copper. There is a brass valve
at the entry. Do I need a dielectric union connected to that valve? Or can I
just connect copper to it? Should I use dielectric unions at the water heater?
What really fails when galvanized and copper pipe are connected together? The
copper? The galvanized? The joint itself?
Is it important to use copper hangers for copper pipe?
Seattle water, if it matters.
I think the copper wire allows the pipe to continue to be a ground,
when someone used copper to galvanised on my pipe it deteriorated and
looked bad fast and I replaced it, on a water heater a thermal break
is needed to help to keep heat in the heater.
Not for corrosion protection, no--the wire is a grounding wire
completing a ground around the dielectric path.
Cu/brass is ok...
The less noble metal is more attacked so steel (Fe) is preferentially
the target. But, there is often less actual Cu physically so it may be
the copper side that actually fails first. Upshot is, it can be either.
A link that has good discussion of galvanic corrosion in water systems
-- it's specifically addressing fire protection systems but the
principles are the same and it's as good/cogent discussion I've seen...
No, galvanic action is a direct contact. The ground wire, while there
is a potential yes, being dry is far less susceptible to the corrosion
and it's there where it can be seen, anyway. The dielectric between the
two water pipes themselves is still between the two dissimilar metals.
It would be nice if they were all the same material, but it's the lesser
of the evils.
Well, no, that's a different connection--it's a direct connection
between the two dissimilar metals so strictly there should be one at
each junction where switching. As noted, brass being a mostly copper
alloy is near enough in potential to not be a problem.
I'm afraid you are wrong there, dpb. the electrical connection between
the two dissimilar metals does NOT have to be in the (wet) electrolyte area.
Just visualize a strip of copper and a strip of zinc joined together at
one of their ends and spread apart at the other. Immerse the spread ends
of the strips in a weakly acidic electrolyte, with the joined ends above
the liquid level.
Doing that effectively creates a battery, with a dead short across its
positive and negative terminals.
The zinc will corrode away pretty fast, even though the "touching" parts
They attach a zinc block to metal parts underwater on boats - sometimes even
with a wire going to an above water connection point. This reduces corrosion of
all the metal connected to it. The corrosion does not just occur at the
connection point. Connect a metal from the other end of the chart the same way -
everything would corrode faster, right?
The also make compatible metal grounding clamps.
However, I've ground connections of copper to galvanized and black iron
that have been in place for 40 years or longer and they simply have not
been a problem.
I just go through saying that -- I was talking of the brass/copper
junction. If you have a brass/galvanized on the other end, it should
also be a dielectric connection.
There are compatible-metal grounding clamps available.
My experience has been however, that the grounding of a copper wire to
either galvanized (scrape through to the underlying iron) or black pipe
has not been a real problem in practice. It just doesn't seem to be an
issue that I've observed at that point.
I am surprised the anode in the tank did not protect the nipples.
Do you suppose the the anode was similarly degraded? Or was it already gone?
I did say that I'd "changed out" (replaced) the heater, and the leak
developed a few month's later. So the anode rod was new.
The adonde doesn't protect the nipples because of the galvanic current
distribution through the electrolyte. It's effect can't "reach up" into
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.