galvanized to brass to copper, how much brass?

[pasadena_commut]

When connecting galvanized pipe to copper pipe through brass how much brass is "enough" to ward off problems with galvanic corrosion?

Is the length of a ball valve sufficient?

In many posts on the web people say to use 6" of brass, but none of them cite their source or explain why 6" is the magic number and not 10", 5", or even 1". Dielectric unions are another way to go about this, and in those the ends of the two dissimilar pipes appear to be at most 1" apart.

Also, when this transition is from the house to the service line, and it is acting as the house ground, I assume that if brass is used nothing else needs to be done to maintain the ground since all of those metals conduct. If a dielectric union is employed presumably two brass clamps on either side with a copper wire connecting them is needed to keep a functioning ground. Does a jumper like that reintroduce problems with galvanic corrosion?

 

[pasadena_commut]

Also...

Why not use a dielectric nipple to connect copper to galvanized? That's what is done on water heaters.
Something like this:

https://www.grainger.com/product/APPROVED-VENDOR-Dielectric-Nipple-1-in-Nominal-4PFZ6
There must be some issue because in all the discussions I have seen on this, nobody has recommended one of these when connecting house galvanized to a new copper service line. I have seen them recommended for making that sort of connection inside a house.

 

[GReynolds929]

UPC 605.16.1
Link

 

[pasadena_commut]

UPC 605.16.1

OK, that code says at least 6". Why did the code make that the minimum length? There must be some reason that is "long enough".

 

[breplum]

Dielectric unions suck bc they enhance clogging right at the galv side fitting. Dielectric couplings are ok. Dielectric nipples are constrictive but technically ok.
Of course ground jumping is necessary and DOES defeat the whole purpose of it all.
If you must keep crappy, terminal and worthless galvanized pipe as temporary, then generally accepted practice is around 5" of brass. We also add a wye strainer to prevent rust clots from contaminating downstream copper in those cases.
The code development has had so many sources. I doubt anyone here knows much about the dielectric etiology.

 

[Bird Doo Head]

I don't know if this is sufficient to stop corrosion, but can you use PEX between the galvanized and copper?
Since PEX is so easy and inexpensive, maybe you'll find yourself changing all the galvanized out while you're at it.

Paul
PS:
Dielectric unions don't electrically isolate the pipes once filled. Since there are minerals & oxygen in the water, there's some continuity on each side of the union. I suppose at best they prevent (or try to prevent) the galvanic corrosion that would occur at the threads if copper and galvanized were screwed directly together.

Regarding bonding, NFPA 70 requirements vary depending if the piping is considered a "system" & if it is likely to be energized. The subject is open to much interpretation. Take a look around NPFA 70 250.104 for a start.

 

[pasadena_commut]

Dielectric unions don't electrically isolate the pipes once filled. Since there are minerals & oxygen in the water, there's some continuity on each side of the union. I suppose at best they prevent (or try to prevent) the galvanic corrosion that would occur at the threads if copper and galvanized were screwed directly together.

Tap water does not conduct well even when it is hard, as ours is. That would offer a very high resistance path to the soil and would make a very poor ground.

 

[Bird Doo Head]

Tap water does not conduct well even when it is hard, as ours is. That would offer a very high resistance path to the soil and would make a very poor ground.

Does that mean it's safe to use a toaster in the bathtub?



PS: At 21.5 degrees-C my Detroit city water measured 1,400 micro Seimens/cm. The toaster stays in the kitchen.

 

[pasadena_commut]

Does that mean it's safe to use a toaster in the bathtub?

No. Experimentally though, it isn't always lethal (at least for a hair dryer):

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2743575/
Also, standing in a running shower with one foot firmly on the metal drain and holding that live toaster tightly to the chest is strongly counter indicated.

I think that in many cases "died in the tub from a hair dryer" is not because the device is in the water per se, but because the person grabbed it with one (wet) hand and lifted it out of the water, or reached outside the tub to grab it, again with one wet hand - making the only (unintended) path to ground through their body. The dryer might end up in the tub when the person dies, but it may not have been in there, fully submerged, when the fatality occurred.

A GFCI in theory should save your bacon in this situation, but I'm very much not motivated to do that experiment!