"dpb" wrote in message ...
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.

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


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...

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


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

Thanks for the reference.