"Rick R" wrote in message
...

"Sacramento Dave" wrote in message
. net...

"chickenwing" wrote in message
oups.com...
how come I wasn't told about this

This is a dielectric union. This device electrically separates the
water heater from the household piping.


http://www.hammerzone.com/archives/p.../union_de/intr
o.htm


They make a Dielectric Nipple. I think that's a better choice

http://acmehardware.com/pd-5338579-D...ic-Nipple.aspx


This is not a Dielectric fitting.
This is just a nipple with a plastic sleeve, that will not insulate from
the current.
You can check this easily with a DMM. Simple continuity test.
Granted I am sure it would not corrode nearly as quickly, as a unlined
nipple. But as soon as water gets between the sleeve and the nipple. There
is a space between the plastic and the nipple from molding. Plastic
shrinks as it cools from the molding process. It will start corroding.

Rick R.

I've been looking for a solution to the galvanic corrosion for many years.
My very hard water after softening is a very conductive electrolyte. Using
brass nipples supplied with a water heater, I got galvanic corrosion of the
tank near the nipples and early tank failure. Switching to galvanized
nipples, the nipples soon corroded at the dielectric connection. The short
path across the insulation is apparently easily bridged in conductive water.
But this is an improvement -- better to replace nipples every year or so
than an early failed heater.

Plastic lined nipples seem to be new to the market. They do provide a much
longer conductive path though the conductive water. I installed a pair a
year ago. The early signs of corrosion I experienced with the previous
steel nipples have not appeared and I am hopeful that this will be a
substantial improvement over the previous solutions. It will take some time
to conclusively prove their value but I am hopeful.

SJF