Dissimilar metals and electrolysis

Koan

I have seen four instances of galvanic corrosion in three different houses here in Maryland. One house on well water, the other three on municipal water. One case was copper to a chrome toilet valve (well water) , one was galvanized connected to copper, two were copper flowing to galvanized. I am attaching a pic of one. Oddly - it did not happen to all the copper to galvanized joints, only some. The pic is of the main feed to the house where I now live.

nicholas bonham-carter

Copper and zinc make a battery with an acidic electrolyte, so it is best to use a brass fitting as a transition piece, instead of the notorious dialectic fittings.--NBC

Koan

@nicholas bonham-carter better yet, here is the roll of 1&1/4 copper K type tubing that will be the new main next to the larger pic of the failing part(at bottom of pic) ! I also bought a brass 90 as an interim solution.

Fred

@Koan, is this a single family residence? An inch and a quarter supply is huge.

Koan

It is! a town house in Baltimore, three floors. Still has one of the original Flushometer toilets. I figured I may as well replace the main feed with copper the same size

Even more odd - take a gander at the pressure gauges. The PRV is shot, it only reduces pressure when the water runs. The reduced pressure gauge is pegged at 100PSI, the street pressure is 120 PSI.

So I have 120 PSI on that corroded joint! Hope I get to it soon enough!

Only good thing is I can use that quarter turn bib to wand out the boiler. I made my wand out of 3/8 tubing - really cleaned out the crud!

Zman

It is common for the water line to be a ground to the electrical system. If it accidentally becomes the only ground, the electrical current can cause accelerated corrosion or even electrical shock.

ratio

It's more than common, it's required by code if it's conductive. And I've had inspectors try to make me bond it even though it wasn't.

Koan

we have an 8 foot copper grounding rod with a ground strap connected to the ground of the main panel on the other side of the house. I will check to see if that is also grounded to the plumbing somewhere.

ratio

Should be bonded at the water entrance & the meter jumped with the same size wire, assuming it's metallic/conductive. I'd have to check the code to make sure. I've been out of the field too long, the code has changed a lot since I did electrical work on purpose.

ChrisJ

In my area we have a ground rod bonded to the panel and the water line must be bonded. I have a jumper across the meter, and the hot water pipe most be bonded as well.

I bonded my gas line, though still unsure if it was necessary as it's all black iron. I figure, it can't hurt.

In the house I grew up in, the only grounding was via the water pipe and of course the neutral going to the pole.

Koan

@ratio the meter is in a pit 35 feet from the house, so no worries there. I should ground through the HWH and make sure the ground rod wire is connected to the plumbing though.

@ChrisJ I think it is against code here to ground gas pipe, but that may be the underground part only.

BUILDING,FIRE, AND RELATED CODES
NEC Art. 280
Section 250.52. Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
{As in NEC}
(B) Not Permitted for Use as Grounding Electrodes.
The following may not be used as
grounding electrodes:
(1) Gas piping or any other metallic piping or tank that contains flammable liquid...

ChrisJ

Koan said:

@ratio the meter is in a pit 35 feet from the house, so no worries there. I should ground through the HWH and make sure the ground rod wire is connected to the plumbing though.

@ChrisJ I think it is against code here to ground gas pipe, but that may be the underground part only.

BUILDING,FIRE, AND RELATED CODES
NEC Art. 280
Section 250.52. Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
{As in NEC}
(B) Not Permitted for Use as Grounding Electrodes.
The following may not be used as
grounding electrodes:
(1) Gas piping or any other metallic piping or tank that contains flammable liquid...

The pipe is bonded to ground, it's not being used as ground.

It cannot be against code as CSST must be bonded.

Fred

Actually I thought (seems I read it in our local building code) that any gas appliance attached to the gas line that also has a properly grounded electrical circuit (like a gas furnace) acts as a bond for the gas line. I can't imagine that an additional bond would hurt but I don't think it's necessary.

ratio

IDK about the equipment grounding conductor counting as a bonding conductor, but what 250.52(B)(1) means is that you can't use the gas line as your Grounding Electrode. Basically, it means that you must drive a ground rod. IIRC you can't even call the water line the Grounding Electrode; but again I'm out of practice & would most certainly refer to the NEC before I made any recommendations on what you should do.

WRT the water heater, nowadays I pipe three ball valves in a bypass configuration so I can remove/replace without draining the system. That kind of eliminates the water tank jumper. Again, I had to argue that with an inspector once, although it didn't take long for the light to go on. (I may have set him up a little—when he asked if I had the water tank jumped I said "Nope". )