current on water line

Status
Not open for further replies.
I got a call from a fellow who said that when the plumber changed his pressure reducing valve it sparked when he installed it. I went to the home to check it and sure enough there are up to 5 amps of current on the water line which is acting as the grounding electrode. In order to isolate it, I shut off the individual circuits only to find that the current flows even with the main service disconnect off. I figured there must be something wrong up on the power company pole but the power company said it was OK. Any thoughts what would cause this?
 

user 100

Senior Member
Location
texas
I got a call from a fellow who said that when the plumber changed his pressure reducing valve it sparked when he installed it. I went to the home to check it and sure enough there are up to 5 amps of current on the water line which is acting as the grounding electrode. In order to isolate it, I shut off the individual circuits only to find that the current flows even with the main service disconnect off. I figured there must be something wrong up on the power company pole but the power company said it was OK. Any thoughts what would cause this?

Are any neighbors having issues? The current from a neighbors home with a loose neutral will flow thru their water pipe gec and then through the municipal metallic water system and will then flow thru your pipes and your gec, finally making its stop at the poco tranny. Another thing is that 5 amps on the pipes on a common city metallic water system isn't considered too far outside the norm-there may or may not be a problem- the metallic pipe if continous will be in parallel with the neutral and some current will be normal.
 
Last edited:

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
In addition to measuring the current, it might be useful to (carefully) measure the voltage with the pipe connection open.
If it is only a volt or two it may be just a "normal" objectionable current caused by less than optimal neutral resistance.
But if if is greater it is a good indication that one of your neighbors has a seriously compromised neutral. Either in customer wiring or service drop.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Retired Electrician
Here's an illustration to go with the other posts.

Neutral2.gif


Roger
 

tom baker

First Chief Moderator
Staff member
This condition is very common. the American water works association (AWWA) estimates there is one water meter reader shocked daily.
With two houses connected with metallic water lines your neutrals are in parallel with the water lines. There will normally be current on the water line.

What the AWWA recommends is installing a short 6-12 inch length of NM pipe on the service line. You'll want to see if the water line was used as a ground and may need to install ground rods.
 
Many thanks!

Many thanks!

Thank you all for the information and that diagram especially. I intend to go back to measure the voltage and I'll inquire about the neighbors and whether or not the water system is all metallic. Really appreciate the help gentlemen.
 

kwired

Electron manager
Location
NE Nebraska
What the AWWA recommends is installing a short 6-12 inch length of NM pipe on the service line. You'll want to see if the water line was used as a ground and may need to install ground rods.
And NEC requires bonding around insulating fitting/sections of piping, as well as commonly replaced components such as meters.

Bonding around a meter in a way that allows removal of the meter without having to remove the bonding jumper leaves the water works employee at very little to no risk when removing a meter. They still are at risk when excavating/repairing a metallic pipe though and need to be trained to install a temporary jumper across any section they intend to create an open circuit as part of their work.
 

paul

Senior Member
Location
Snohomish, WA
And NEC requires bonding around insulating fitting/sections of piping, as well as commonly replaced components such as meters.

Bonding around a meter in a way that allows removal of the meter without having to remove the bonding jumper leaves the water works employee at very little to no risk when removing a meter. They still are at risk when excavating/repairing a metallic pipe though and need to be trained to install a temporary jumper across any section they intend to create an open circuit as part of their work.

These are still band-aids that don't fix the actual problem.
 

kwired

Electron manager
Location
NE Nebraska
These are still band-aids that don't fix the actual problem.
If you are going to bond metallic pipes that run between separate facilities to the grounded conductor - then you are creating parallel paths for current on grounded conductor to flow. Current flows on all available paths and there is no way to prevent this other then intentional isolation, yet NEC requires us to use such piping as a grounding electrode and to bond interior piping leaving us little choice on preventing such current other then to not use metallic piping.
 

kwired

Electron manager
Location
NE Nebraska
I don't understand, I was under the impression you folks across the pond don't use the MGN system we do here.

I am more confused about the drawing showing what appears to be single phase three wire to each home, I thought they typically have three phase wye transformers(416/240 volts) and each house would still be on common neutral conductor but each one would typically be on a different phase.

I don't know if they bond a primary conductor to a secondary conductor, but you could still have the grounded conductor "stray currents" in that situation on the secondary though.
 

Buck Parrish

Senior Member
Location
NC & IN
My brother's a plumbing contractor. When they cut the old metal water pipe. All the lights went out in the house next door.

Some areas use rubber in between the water meters to prevent this from happening.
 

TommyO

Member
Location
Sunnyvale, CA
I am more confused about the drawing showing what appears to be single phase three wire to each home, I thought they typically have three phase wye transformers(416/240 volts) and each house would still be on common neutral conductor but each one would typically be on a different phase.

I don't know if they bond a primary conductor to a secondary conductor, but you could still have the grounded conductor "stray currents" in that situation on the secondary though.

If the houses are far enough apart there might be a transformer for each house.
But often multiple houses are fed from one phase of one transformer.
For my own house it has an underground feed. The connection to the utility is waterproof connectors that also connect my neighbor's feed. So between my house and the neighbor electrically it's pretty much a direct connection (just meters, wire, and a connector)
And I've seen overhead feeds where it looks to me like the wires for 3 adjacent houses terminate to the same spots on the transformer.
 

kwired

Electron manager
Location
NE Nebraska
If the houses are far enough apart there might be a transformer for each house.
But often multiple houses are fed from one phase of one transformer.
For my own house it has an underground feed. The connection to the utility is waterproof connectors that also connect my neighbor's feed. So between my house and the neighbor electrically it's pretty much a direct connection (just meters, wire, and a connector)
And I've seen overhead feeds where it looks to me like the wires for 3 adjacent houses terminate to the same spots on the transformer.

My reply you quoted was to typical European installations where they have 415/240 volt wye systems but each home/small business usually only is supplied with one phase and the neutral conductor (240 volts single phase essentially at the customer facility)

In North America you may have multiple customers fed from one transformer - especially for small 120/240 single phase use customers, but other then an occasional 120 volt only service (usually an old existing service at that) they all get supplied with every conductor of the system. Multi tenant applications on a three phase wye is about the only place you see only a part of the system available to each tenant. High leg delta systems are a different breed though - quite often you have a lot of 120/240 single phase services but an occasional customer that needs the third phase - but they build those systems with multiple single phase transformers and put in a smaller pot for the high leg that has lighter load on it.
 

TommyO

Member
Location
Sunnyvale, CA
My reply you quoted was to typical European installations
Sorry - I misread you - you said you weren't understanding the picture. The picture is of normal US setup and the thread has been about US. And with the reference to "across the pond" I assumed you were the European.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
It is about how open POCO neutrals can lead to residence wiring being energized even after meter has been pulled. And how a high resistance ground fault can slowly carbonize building materials to the point of ignition.
Well worth watching.
 
Status
Not open for further replies.
Top