Supplementing metal water pipe

[El3ktrishun]

It seems pretty common place around here to use the water piping as the grounding electrode. But also seems to be common place to then drive 2 rods as the supplemental. I can admit that I’ve done this many times just because that’s how I was taught to do it. But now that I’ve been reading into this my understanding is that if I use the water pipe as my main grounding electrode then I only need to drive ONE rod as a supplemental. A second rod would only be needed in the instance where there is no water pipe and I’m using the first ground rod as my main grounding electrode (or 25 ohms or less can be proved at first rod)?

 

[infinity]

A water pipe electrode is required to be supplemented by an additional electrode. A single rod would only qualify as the additional electrode if it were tested and proven to be 25 ohms or less. Since almost no one bothers to test the single rod most electricians just install two rods and they're done. An untested single rod is not considered an electrode.

Welcome to the Forum.

 

[mtnelect]

Just a reminder, installing a ground rod requires contacting "Underground Service Alert".

 

[infinity]

Just a reminder, installing a ground rod requires contacting "Underground Service Alert".

No one does that around here. There are occasional mishaps.

 

[El3ktrishun]

A water pipe electrode is required to be supplemented by an additional electrode. A single rod would only qualify as the additional electrode if it were tested and proven to be 25 ohms or less. Since almost no one bothers to test the single rod most electricians just install two rods and they're done. An untested single rod is not considered an electrode.

Welcome to the Forum.

The only thing I can find about a single rod at 25ohms or less is 250.53(a)2 exception: if a single rod pipe or plate grounding electrode has a resistance to earth of 25 ohms or less, the supplemental electrode shall not be required. So what I’m getting out of this is that only 1 rod required if it’s the supplemental and only 1 rod if it’s your main electrode if you can prove 25 ohms or less. Am I reading this correctly?

 

[roger]

Read 250.53(D)(2), the supplemental rod would have to meet the requirements of 250.53(A)(2)

 

[roger]

IMO, the wording of 250.53(D)(2) needs to be worked on, if a single rod is supplementing a water pipe electrode then the water pipe electrode is also supplementing the rod.

 

[infinity]

So what I’m getting out of this is that only 1 rod required if it’s the supplemental and only 1 rod if it’s your main electrode if you can prove 25 ohms or less. Am I reading this correctly?

The NEC does not use the term main electrode but because some electrodes require supplementation I can see why people think of it that way. The purpose of using a supplemental electrode for the water pipe is because the water pipes get replaced with non-metallic pipe and the water pipe electrode is now gone. That leaves the supplemental electrode as the only electrode. A single rod unless tested to prove that it's 25 ohms or less is not an electrode.

Roger is correct that this section could use some work on the wording. The intent of a supplemental electrode for a water pipe is that it can stand alone as an electrode if the metal pipe is removed.

 

[Electromatic]

I have problems with the almost circular reasoning and verbiage in the section, also. I had a thread on it, but it must be too old to still find.

My understanding, roughly, is:

• 250.53(D)(2) Says a metal underground water pipe shall be supplemented by another electrode of the types described in 250.52(A)(2)-(8)
• If that supplemental electrode is a single rod...
• 250.53(A)(2) Says a single rod shall be supplemented by another electrode of the types described in 250.52(A)(2)-(8)
• The water pipe and a single rod can't supplement each other because the water pipe is an electrode under 250.52(A)(1), not (A)(2)-(8)

 

[LarryFine]

I think the way we reconcile it is that we look at the pair of rods as a single qualified electrode.

 

[infinity]

I think the way we reconcile it is that we look at the pair of rods as a single qualified electrode.

That's how I've always viewed it. The only way that a ground rod can be an electrode is that it has been tested for 25 ohms or less or is supplemented by another rod or electrode.

 

[LarryFine]

The only way that a ground rod can be an electrode is that it has been tested for 25 ohms or less or is supplemented by another rod or electrode.

And we all know which method is easier, cheaper, and faster to implement.