GEC starts from the meter to a grounding rod and ends at CU water pipe

Good evening. I am in the process of completing the120-hr pre-licensing course. My house has #4 stranded CU GEC coming out of meter box, goes through an acorn clamp at the grounding rod, and ends at the CU water pipe. The SE conductor at the main breaker is 4/0 aluminum. Does the grounding rod in this system consider a supplement to the water pipe? Or Does this need another grounding rod installed separated at least 6 feet from the existing rod? Thank you very much.

The rod would be the supplemental electrode to the water line connection.

Thank you.

Also unless it’s proven that the resistance of the single rod is 25Ω or less another electrode is required, typically a second rod.

I was thinking about this requirement. Does this requirement apply to this case also where the grounding rod is also connected to the water pipe?

LOL! Let’s all figure that one out…
Where is my meter.

Yes, the water pipe needs to be supplemented by an additional electrode. In order for a ground rod to qualify as that additional electrode it needs to meet one of two options, it needs to be 25Ω or less or there needs to be two of them minimum 6’ apart.

This is a good video on resistance.

Not to split hairs, but…

I’m not sure we can assume the water pipe connection is the primary grounding source. In fact, in my area I would be certain that the water pipe is NOT the primary grounding source since 90%+ of our main water-lines are plastic.

When I read the OP, my first inclination was that the ground-rod serves as the GE and the water pipe connection is just the common bond between metallic piping and the GE.

Do you know why someone would prescribe the use of the water pipe as a grounding electrode as it has to be supplemented? The supplemental electrode makes the water pipe redundant and unncessary, does it not? if not, in what cases?

The NEC requires that the water pipe must be used as an electrode if it’s metallic and at least 10’ of it is buried in the earth. The reason that a supplemental electrode is required is so that if the pipe is changed to plastic in the future there will still be a grounding electrode system.


Question, water is a conductor as well. Could it be that if grounded to a metal pipe it will conduct itself to the water through the pipe? :exploding_head:

Are you saying the use of the water pipe (if metal, 10f, etc…) as a choice of a grounding electrode is not optional? Where in NEC does it says this? If you are not saying this, my question still stands :slight_smile:

Nooo sir. I’m just asking about the physical attributes of electricity. FOOD FOR THOUGHT. I’ve assisted in many installations of main and sub-panels which included grounding rods and clamping a water line. By all means, go with the NEC.

Water is a poor conductor, distilled water is nonconductive. With due respect, what you stated has nothing to do with what I am asking.


However, you can eliminate it under 250.6 Objectionable Current.

Yes the NEC requires that you connect all electrodes that are present at the building or structure.

Part III. Grounding Electrode System and Grounding Electrode Conductor
250.50 Grounding Electrode System. All grounding electrodes as described in 250.52(A)(1) through (A)(7) that are present at each building or structure served shall be bonded together to form the grounding electrode system. Where none of these grounding electrodes exist, one or more of the grounding electrodes specified in 250.52(A)(4) through (A)(8) shall be installed and used.

250.52 Grounding Electrodes.
(A) Electrodes Permitted for Grounding.
(1) Metal Underground Water Pipe. A metal underground
water pipe in direct contact with the earth for 3.0 m (10 ft) or
more (including any metal well casing bonded to the pipe) and
electrically continuous (or made electrically continuous by
bonding around insulating joints or insulating pipe) to the
points of connection of the grounding electrode conductor
and the bonding conductor(s) or jumper(s), if installed.

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If the water line is plastic there would be no need to even run a bond conductor to it.

The OP said the water line was copper so it needs to be at least bonded and it would be an electrode that needs to be used if it extends at least 10 foot outside the building.

The surface area of a public water system with its network of metallic piping would be a huge electrode with very low resistance.

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The OP didn’t specify whether the CU “water line” was the main supply or the piping within the residence. Even if the main supply line is plastic, the copper piping of the residence is also required to be bonded to the GE.

Good discussion either way…

True, there is some ambiguity over where this is the incoming water or just a bond. Initially I thought of incoming since it was connected to the rod.