Bob F wrote:
"dpb" wrote in message ...
....
Not for corrosion protection, no--the wire is a grounding wire completing a
ground around the dielectric path.

Right - but does it defeat the protection offered by the dielectric union?

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.

Cu/brass is ok...

Even when the other end of the valve is connected to galvanized outside pipe?

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.

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