Objectionable Current - Water main

[W@ttson]

Hello all,

Usually, we battle objectionable current within residential, commercial, or industrial facilities and view the water main outside in the street as a completely foriegn system that we don't need to deal with. We keep it in mind when we talk about having objectionable current or harmonics leak into the common street water main and over into our own systems from neighbors but what if we are actually going to work on the water main?

I have a project where a water main needs to come above ground for a street crossing. It is an old metal water main. It has been identified that the water main has stray current people have felt "shocks" from it.

In the electrical industry we know that sometimes the water main reluctantly becomes a "backup neutral" whenever there is an incorrect wiring situation on a premisis or a neutral connection to a facility is severed since the NEC requires that the water line coming into the facility be bonded to the neutral at the service equipment. If the neutral conductor is removed, the only way back to the source is through the water pipe coming to the house and then ultimately to the water main and hitching a ride back to the service transformer via a neighbors neutral line.

Two questions:
1. How do you make the water main safe so pedestrians do not get shocked?
2. When the utility works go to work on water mains, how do they not get zapped when there is often objectional current on the water main?

 

[W@ttson]

My suggestion to #1 is to bond the section immediately coming up out of the ground and then bond the portion immediately going back into the ground and then bond those two together. Take those bonding jumpers to the near by utility transformer secondary and bond it there to the ground bar.

It is not reasonable to go door to door chasing where the stray current is coming from. I just need to find out how best to make it safe.

 

[don_resqcapt19]

Hello all,

Usually, we battle objectionable current within residential, commercial, or industrial facilities and view the water main outside in the street as a completely foriegn system that we don't need to deal with. We keep it in mind when we talk about having objectionable current or harmonics leak into the common street water main and over into our own systems from neighbors but what if we are actually going to work on the water main?

I have a project where a water main needs to come above ground for a street crossing. It is an old metal water main. It has been identified that the water main has stray current people have felt "shocks" from it.

In the electrical industry we know that sometimes the water main reluctantly becomes a "backup neutral" whenever there is an incorrect wiring situation on a premisis or a neutral connection to a facility is severed since the NEC requires that the water line coming into the facility be bonded to the neutral at the service equipment. If the neutral conductor is removed, the only way back to the source is through the water pipe coming to the house and then ultimately to the water main and hitching a ride back to the service transformer via a neighbors neutral line.

Two questions:
1. How do you make the water main safe so pedestrians do not get shocked?
2. When the utility works go to work on water mains, how do they not get zapped when there is often objectional current on the water main?

That would indicate either there is so much current on the pipe, that there is enough voltage drop to energize the pipe to a voltage that people can feel. This is not very likely,
You can run hundreds of amps of neutral current on a metal water pipe without creating a shock hazard. Just because it is conducting current does not mean there is a shock hazard.
You could have a lot of neutral current and some high resistance pipe joints that might result in a shock hazard.

 

[W@ttson]

That would indicate either there is so much current on the pipe, that there is enough voltage drop to energize the pipe to a voltage that people can feel. This is not very likely,
You can run hundreds of amps of neutral current on a metal water pipe without creating a shock hazard. Just because it is conducting current does not mean there is a shock hazard.
You could have a lot of neutral current and some high resistance pipe joints that might result in a shock hazard.

This is probably a 100 year old water main in a large city (also near some rail road 3rd rail). It undoubtedly has rust and some higher impedance joints/connections.

The fact is that there are two locations with identical setups. This location has had complaints with shocks from the water main. It is now guarded off. The other location is not guarded off and there have been no shocks.

When water utility works replace water mains, how do they avoid being shocked by breaking pieces of metallic water line that as you say may carry lots of amps. If they break the pipe and touch the two ends, it can put the worker in series with the current.

How do you make this water pipe safe for the public?

 

[Dsg319]

This is probably a 100 year old water main in a large city (also near some rail road 3rd rail). It undoubtedly has rust and some higher impedance joints/connections.

The fact is that there are two locations with identical setups. This location has had complaints with shocks from the water main. It is now guarded off. The other location is not guarded off and there have been no shocks.

When water utility works replace water mains, how do they avoid being shocked by breaking pieces of metallic water line that as you say may carry lots of amps. If they break the pipe and touch the two ends, it can put the worker in series with the current.

How do you make this water pipe safe for the public?

I’d say most seasoned plumbers probably carry a jumper cable.

 

[W@ttson]

I’d say most seasoned plumbers probably carry a jumper cable.

This is for the giant water main in the street that services the whole street. That is above ground to avoid items below ground. That is what is going to be replaced. How do utility works replacing water mains stay safe? I can’t imagine they come with a jumper cable that is 80’ long with clamps to go around a 14” water main. I need to offer a permanent solution for the the utility workers to stay safe and the public so that they can get close to the water main and not get shocked.

It’s something like this:

 

[Dsg319]

This is for the giant water main in the street that services the whole street. That is above ground to avoid items below ground. That is what is going to be replaced. How do utility works replacing water mains stay safe? I can’t imagine they come with a jumper cable that is 80’ long with clamps to go around a 14” water main. I need to offer a permanent solution for the the utility workers to stay safe and the public so that they can get close to the water main and not get shocked.

It’s something like this:

Wow that is big. Sorry I misunderstood your scenario.

But as far as permanently stoping utility/customer neutral current from being objectionable on piping I really do not know.

The NEC already dug its grave making us use waterlines for the grounding electrode system.

 

[tom baker]

I worked for a mid size water utility for 38 years (largest main was 36”). Maint crewd never discussed need to bond around water mains during repairs. Perhaps it was the mains are in a grid or parallel layout.
There were often individual customer service lines with current from open neutrals, POCO would be called to correct

 

[tom baker]

And this is only an issue in areas with metal water service lines.

 

[winnie]

You can't fix the problem without knowing what the problem is.

If you have current flowing along the pipes, then you won't have a problem until the pipes get 'broken' by pipe workers replacing sections. The solution in thus case is bonding around the section being opened.

But you are describing people being shocked when touching intact piping. This suggests potential gradients in the soil surrounding the pipes, which to me screams something injecting current into the soil.

A band-aid solution might be equipotential bonding around the pipes, installing a tapering ground grid so that the soil near the pipes is bonded to them. However this just pushes the problem away from the pipes, it doesn't solve the problem.

I think you need to map the soil potentials to find the source injecting the current.

Jonathan

 

[W@ttson]

You can't fix the problem without knowing what the problem is.

If you have current flowing along the pipes, then you won't have a problem until the pipes get 'broken' by pipe workers replacing sections. The solution in thus case is bonding around the section being opened.

But you are describing people being shocked when touching intact piping. This suggests potential gradients in the soil surrounding the pipes, which to me screams something injecting current into the soil.

A band-aid solution might be equipotential bonding around the pipes, installing a tapering ground grid so that the soil near the pipes is bonded to them. However this just pushes the problem away from the pipes, it doesn't solve the problem.

I think you need to map the soil potentials to find the source injecting the current.

Jonathan

My first though is broken neutral to one of the busniesses nearby. This is very old infrastruture with many people changing ownership through the years. Each of which doing who knows what to the electrical service. The services to those businesses are underground so very likely there is an issue even just getting to those businesses.

However, the fact that there is also a rail road nearby has me thinking that that it can also be issues arising from their electrification. They have third rail along the tracks and likely use one of the tracks as a return.

 

[don_resqcapt19]

This is for the giant water main in the street that services the whole street. That is above ground to avoid items below ground. That is what is going to be replaced. How do utility works replacing water mains stay safe? I can’t imagine they come with a jumper cable that is 80’ long with clamps to go around a 14” water main. I need to offer a permanent solution for the the utility workers to stay safe and the public so that they can get close to the water main and not get shocked.

It’s something like this:

If you can't get close to the pipes or even touch them, there is something seriously wrong with the electrical systems in the area, maybe even at the distribution voltage levels. I think you need to get the electric utility involved and have them start opening circuits until the voltage goes away to locate the electrical problem.voltage is.

If the pipe is the only path, then the open circuit voltage across the pipe ends will be the line to neutral voltage of the power system. If there is an intact service neutral conductor, then the open circuit voltage across the pipe ends would only be the voltage drop on the service neutral conductor.

 

[don_resqcapt19]

Wow that is big. Sorry I misunderstood your scenario.

But as far as permanently stoping utility/customer neutral current from being objectionable on piping I really do not know.

The NEC already dug its grave making us use waterlines for the grounding electrode system.

If the water people see this as a real problem, they can fix it in their codes. Simply require a short length of nonmetallic pipe between the water main and the building.
However, this issue is rapidly going away, as there is not a lot of metallic water mains being installed any more...none in my area. All replacements and new mains are non-metallic.

 

[tom baker]

My first though is broken neutral to one of the busniesses nearby. This is very old infrastruture with many people changing ownership through the years. Each of which doing who knows what to the electrical service. The services to those businesses are underground so very likely there is an issue even just getting to those businesses.

However, the fact that there is also a rail road nearby has me thinking that that it can also be issues arising from their electrification. They have third rail along the tracks and likely use one of the tracks as a return.

Third rail systems are DC power, that DC wants to go to its source via a well grounded track

 

[kwired]

Would not necessarily need a jumper with a clip that can open 14". Either clamp onto flange, taps or tees that are smaller or come up with some sort of fitting you can add on to the pipe that also has smaller dimension place you can clamp on with a smaller clamp May possibly need to remove paint or other coatings to assure best contact.

This is for the giant water main in the street that services the whole street. That is above ground to avoid items below ground. That is what is going to be replaced. How do utility works replacing water mains stay safe? I can’t imagine they come with a jumper cable that is 80’ long with clamps to go around a 14” water main. I need to offer a permanent solution for the the utility workers to stay safe and the public so that they can get close to the water main and not get shocked.

It’s something like this:

 

[W@ttson]

If the water people see this as a real problem, they can fix it in their codes. Simply require a short length of nonmetallic pipe between the water main and the building.
However, this issue is rapidly going away, as there is not a lot of metallic water mains being installed any more...none in my area. All replacements and new mains are non-metallic.

Unfortunately, this replacement will also be metallic.

 

[W@ttson]

Would not necessarily need a jumper with a clip that can open 14". Either clamp onto flange, taps or tees that are smaller or come up with some sort of fitting you can add on to the pipe that also has smaller dimension place you can clamp on with a smaller clamp May possibly need to remove paint or other coatings to assure best contact.

So my first hunch of bonding both ends, part that emerges from ground, and part the dives back into the ground, was more or less in the right direction?

 

[W@ttson]

Third rail systems are DC power, that DC wants to go to its source via a well grounded track

I think there is a Mike holt video on objectionable current where he mentions rail roads installed near a hospital was producing a lot of objectionable current which the hospital objected to.

 

[Dsg319]

If the water people see this as a real problem, they can fix it in their codes. Simply require a short length of nonmetallic pipe between the water main and the building.
However, this issue is rapidly going away, as there is not a lot of metallic water mains being installed any more...none in my area. All replacements and new mains are non-metallic.

Same here.

 

[GoldDigger]

If there is a problem with one or more houses or businesses putting large neutral current on their GES and from there into the water main, there will certainly be a hazard if a plumber breaks the continuity of the connection between building piping and the main.
Whether there will be a problem if the continuity of the main is broken will depend on whether the current has an alternate path back into a nearby GES and from there to the POCO neutral or there is a low enough earth impedance from the affected main segment to limit the voltage.
Most to the time there will not be a significant hazard, but in less densely developed areas where there is long distance between customers the risks are higher.
Similarly, if the water main is electrically continuous but coated, the problem could extend over a longer distance.