Current through main water pipe in house

[jeff48356]

I've never seen this before, but I just got a call from a plumber that I occasionally work with, and he discovered a serious electrical issue. The house was built in 1957, and has galvanized water piping. The GEC consists of a ground wire attached to a section of cold water pipe near the panel, and another across the water meter in the basement. When the plumber disconnected the wire across the water meter to do a re-pipe of the house (with PEX), it sparked and all the lights in the basement went dim. He hooked it back up and advised the homeowner that he couldn't do the plumbing until an electrician remediated the grounding problem. I went out there today and measured the current through the pipe to be 2.6A.

What might cause this? I pulled the electric meter outside and took what appear to be normal voltage readings inside the meter base. When I turn off the main breaker, the current goes to zero, so the issue must be somewhere within the house.

 

[winnie]

This is a classic symptom of a compromised neutral somewhere.

The water pipe is probably connected to a metal water main and from there to other houses with their neutral to ground bonds. The water pipe becomes a backup neutral.

Jon

 

[Little Bill]

Also, tell the plumber that in the future to not cut or take loose any jumper wire across the meter. He was lucky he only SAW sparks, he very well could have FELT them! The jumper is there for that reason, so as not to have a potential difference between the piping before & after the meter.
The house probably has been using the water pipe as a neutral for a while and not noticed until the pipe was cut.

 

[Cow]

The neutral wire and connections from the main service panel to the utility transformer needs to be checked.

Your customer is most likely using the the neighbors neutral, by way of a common water pipe grounding electrode, as a return path for their neutral current.

 

[synchro]

I would first turn off individual branch circuit breakers to see if one of them makes the current in the pipe go away. There could be a device on a branch circuit where the equipment ground was connected to a terminal that should have had a neutral wire.

 

[Hv&Lv]

First check the neutral connection behind the meter, then call the utility for this problem. I would guess it’s either a bad neutral connection at the weather head or at the pole. We have had this situation before with plumbers on older houses, and even with CATV repairmen. Our neutral connection is bad somehow, and the house was using the CATV bond for neutral.

 

[Jon456]

Also, tell the plumber that in the future to not cut or take loose any jumper wire across the meter.

I understand the reasoning behind this statement. But as a practical matter, how else is the plumber to replace the old metallic pipe if he's not permitted to first remove that jumper?

I imagine that the GEC from the panel to the water pipe should be disconnected before the bonding jumper across the meter is disconnected. But in this scenario, disconnecting the water pipe GEC at the panel would be just as hazardous. And certainly not within the scope of a plumber's work.

Are there any regulations or codes that stipulate an electrician must remove all GEC's from metallic water pipe before a plumber can remove and replace the pipe?

 

[GoldDigger]

Quick distinction: If current in GES goes away when main is opened, local neutral is compromised. If it is unchanged, a neighbor's neutral is compromised and he is using your neutral.

 

[al hildenbrand]

I understand the reasoning behind this statement. But as a practical matter, how else is the plumber to replace the old metallic pipe if he's not permitted to first remove that jumper?

To only install the pex and remove the metallic water pipe system, the plumber is altering the Electrical Service Configuration and s/he is not licensed to do so. And, if there is a service entrance grounded conductor failure, the plumber isn't generally, by license and training, expected to ensure the continuity of the Grounding Electrode System without interruption prior to removing the metal water pipe system.

The plumber that designs the plumbing alteration (replacement of a legacy metallic water pipe system with a pex system) has to verify that a surviving metallic underground water pipe service is connected FIRST to a Grounding Electrode Conductor from the Electrical Service that will not be interrupted by the plumbing work.

 

[Jon456]

Ok, but the water pipe cannot be the sole electrode of the GES, per NEC 250.53(D)(2). Although I don't know when this went into effect, so there are probably old houses that only have the GEC connected to the water pipe.

The bigger problem, as I see it, is that even with a supplemental electrode, the condition is still dangerous. If the service neutral is severed and power is flowing along the metal pipe to a neighbor's neutral, having a ground rod won't in place won't mitigate that hazard: the ground rod will always have a much higher resistance. And it certainly won't help if it's the neighbor's neutral current that's flowing into your house!

 

[al hildenbrand]

Ok, but the water pipe cannot be the sole electrode of the GES, per NEC 250.53(D)(2). Although I don't know when this went into effect, so there are probably old houses that only have the GEC connected to the water pipe.

The supplementing of the underground metal water pipe started with the 1968 NEC, as I recall. The description of the house in the OP is exactly what would have come to us from the late Forties through the Sixties.

Or before, for that matter.

 

[Jon456]

Since the OP stated that the house was built in 1957, I suspected that it may be before a supplemental electrode was required. Nevertheless, adding a ground rod (or even several ground rods) still won't eliminate this particular hazard.

 

[LarryFine]

When the plumber disconnected the wire across the water meter to do a re-pipe of the house (with PEX), it sparked and all the lights in the basement went dim.

This is all you should need to hear to know the service neutral is broken, and should immediately be remedied.

 

[GoldDigger]

:thumbsup:

 

[ptonsparky]

This is all you should need to hear to know the service neutral is broken, and should immediately be remedied.

And the plumber knew it!