Boden wrote:

Jeff Wisnia wrote:

Sac Dave wrote:

"Big Al" wrote in message
...

Question: Have a 3/4" copper to galvanized pipe junction, has a 6"
brass nipple between them. Is this the proper way to do this to
prevent electrolysis?

Other than on a water heater, when would one use an electrically
isolated union? And why?

Al


Brass is neutral metal and will work.



I'd love to hear what makes you think brass is a "neutral metal", Sac
Dave.

Have you ever even bothered to look at a galvanic table?

Try spending some time reading articles like this one:

http://tinyurl.com/5sekem

before you hand out totally incorect advice.

*******

Regarding the OP's mention of water heaters, the use of dielectric
unions on them is passe, as stated by Rheem in this bulletin:

http://tinyurl.com/5e56ub

Although I realize that this is not a group organized to further
literacy the first sentence of the Rheem bulletin is not one that
portends great understanding.

The second sentence is more worrisome. "... a shut-off valve in at
least the cold inlet waterline is recommended,..." Where would another
other shut-off valve be placed? In the only other waterline, the hot
water outlet? This is an implied prescription for a bomb, and violates
every plumbing code that I'm familiar with.


I won't quibble with you about plumbing codes, as I'm not a mavin about
them, and it is not unreasonable to expect they'd prohibit hot side
shutoff valves on water heaters.

But how did you come up with "This is an implied prescription for a bomb"?

Can you answer these questions?

Do you know what a T&P valve is and why they're code required on water
heaters?

How is having a closed shut off valve on the hot side of a water heater
significantly different than having all "hot" faucets downstream of the
water heater closed, as they usually are for many hours at a time in an
average household?

Now please defend your "bomb" statement.

*********************************************

BTW, dielectric unions do have their uses in specific situations. One
application I remember is the need to use them in natural gas lines when
they enter a building.

Back in the days when all gas mains buried under streets were iron pipe
(pre-plastic pipe era.) "impressed current cathodic protection systems"
were used to prevent corrosion of those mains.

http://en.wikipedia.org/wiki/Cathodi...sed_current_CP

Dielectric unions were installed ahead of the gas lines where they
entered buildings to avoid having gas appliances (such as water heaters)
from shorting those electrified gas mains to ground.

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.

The rest of the piece is an attempt at explaining electrochemistry which
is much better done in a plethora of texts.

So??

Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat '57 EE)
The speed of light is 1.98*10^14 fathoms per fortnight.