How do I ground copper water pipes to old iron water pipes?

September 28, 2006 11:29 AM

How do I ground copper water pipes to old iron water pipes?

I have an old house where the oldest plumbing is iron, and the newer plumbing is copper. I want to fit in a water filter on the iron pipe, but use copper fittings. I have heard that if they aren't ground properly they corrode. Unfortunately, replaceing the iron pipes is not an option.

Bonus question: can you solder copper fittings directly to iron pipe?

posted by kuujjuarapik to home & garden (5 comments total)

First, they probably aren't iron - they are likely galvanized, commonly & incorrectly called iron (I assume they are about 3/4" in diameter with threaded ends).

If that's the case what you're looking for here is a dialectric union, which is used to connect different metals and prevent electrolysis.

Bonus answer: no soldering on galvanized pipe, those are generally threaded. The link above has details.
posted by true at 11:37 AM on September 28, 2006

To connect iron to copper, you generally have to use a threaded copper connector at the joint. One side is a smooth fitting soldered to the copper pipe, and the other is threaded to connect to the iron.

You can try to thread the end of your existing iron pipe, but it's generally "easier" to go back to the nearest elbow on the iron, put the new fitting there, and then run copper pipe to the new device.

Bewarned, if the iron has been there any length of time, it may not want to come apart and may be thoroughly corroded inside...I've had old galvanized pipes simply crush when I went to undo them.

You can also generally buy brand new iron fittings at most home centers, so you could simply pipe in the new filter using iron pipe.

You will not be able to connect the two with solder, generally speaking, and get a good joint.

By virtue of the two pipes being joined, they're already grounded. All metal plumbing pipework is generally speaking grounded to earth, so an extra ground on the copper section isn't going to do anything, I don't think.
posted by maxwelton at 11:41 AM on September 28, 2006

One thing I forgot - be careful of this - if it is an older house your electrical system may be grounded through your water pipes. If that's the case the dialectric will break that loop and could be very dangerous. You'll need to make sure that isn't the case and bond/ground appropriately. You could also use a small length (6" or so) of brass pipe to connect instead of the union - here's a discussion about some of the issues. Code in your area is the authority, of course.
posted by true at 11:41 AM on September 28, 2006

Oops, true beat me to it with a better answer.
posted by maxwelton at 11:41 AM on September 28, 2006

Looks like I'll get started. Thanks!
posted by kuujjuarapik at 11:46 AM on September 28, 2006