Bob F wrote:
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?

Not for corrosion protection, no--the wire is a grounding wire
completing a ground around the dielectric path.

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?

Cu/brass is ok...

What really fails when galvanized and copper pipe are connected together? The
copper? The galvanized? The joint itself?

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.

Is it important to use copper hangers for copper pipe?

Yes.


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...

http://www.copper.org/applications/p...r_systems.html

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