Shock Hazard.

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VIC1958

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I recently had a conversation with a individual from our water department. He told me that he was changing out a meter in a single family residence. While he was removing the jumper, he noticed that it was arcing. He called the City Electrical Department who came out wit ha meter and they were getting reading of around 5 amps. The only other information I could get was that there was no ground rod present and that the neutral conductor at the weather head had corroded and was either making very poor contact or no contact at all. I have not been out to verify or see for myself what is(was) going on. What scenarios could be going on here? I can think of a couple but curious as to what others thought.
 
The water pipe is a parallel path for the neutral in many cases, so even with the neutral in perfect condition there will be current on the water pipe and this current can cause an arc when the piping is being disconnected. If the neutral is in good shape, there is no real shock hazard as the only voltage between the open parts of the water pipe is the voltage drop on the service neutral conductor, but if the service neutral conductor is open or has a high resistance connection, the voltage across the open parts of the water pipe will be a serious shock hazard.
 
lakee911 said:
Agreed.

Theoretically speaking, is it possible to have enough fault current to exhibit this while the neutral is still intact?
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The real question is what voltage is present on the neutral relative to ground when the water pipe ground electrode is interrupted.
If the neutral resistance is 1 ohm, then the voltage on the neutral with an unbalanced load of 20A in the house would be 20V and the home owner is going to see really severe light dimming and brightening as well as damage to electronic equipment.
If the neutral is in really bad shape and the other local ground electrodes are no better than normal, interrupting the water pipe ground could put 100V or more on the inside pipes and create a very serious safety hazard.
On the other hand with a neutral voltage offset of only a couple of volts (corresponding to .1 ohm and 20A load) you can still get a nice fat spark when connecting and disconnecting a low resistance water pipe path.
 
So it may or may not be a hazard.

But isn't that why the jumper is usually made long enough to replace the meter without removing the jumper?

IMO The water dept. should not be removing the jumpers without adding a temporary jumper, or without making sure no shock hazard is present.
 
We must keep in mind that the water pipe and the service neutral are two parallel resistors, there may be other parallel paths such as the cable and phone lines that also parallel the neutral but the water pipe if unbroken to the city main will be a very low impedance when compared to all the other paths, if we look at the ratio of the impedance of the water pipe and the service neutral we may find that the water pipe can be handling as much as 75% or more of the neutral current because it is a really big conductor, it doesn't mean the voltage drop of the neutral will cause a large voltage across the opening if the water pipe is opened but people who are not familiar with parallel neutral current paths and when they see a spark they tend to freak out, sure if the service neutral connection is damaged then we need to dig further and the first test to make is to put an amp meter on the main service neutral going back to the transformer to see if it is carrying some of the current, by putting an amp probe around the two hots (ungrounded) conductors you will see what the neutral should be carrying, but this will be divided up between all paths, so by taking amp reading on the GEC's and the neutral they should sum up to this figure, if you find that the neutral has no current you know you have a bad neutral connection.
 
Had a call years back that the lights in the house would get brighter when the a/c came on. I asked to verify that they were getting brighter, not dimmer, the reply was brighter.

Asked if it could wait a couple of days, answered yes. Next day call said there was arcing behind his electric stove.

Went out. The range was electric, but had gas ran to range location, in-case they ever wanted to change. Arcing was occurring, and the gas pipe had pits in it due to the arcing. Checked the outside main panel & found very loose neutral (had used the ground strands from the outer wrapping of SEU cable for the neutral). Tightened wires, problem fixed.
 
JDB3 said:
Had a call years back that the lights in the house would get brighter when the a/c came on. I asked to verify that they were getting brighter, not dimmer, the reply was brighter.

Asked if it could wait a couple of days, answered yes. Next day call said there was arcing behind his electric stove.

Went out. The range was electric, but had gas ran to range location, in-case they ever wanted to change. Arcing was occurring, and the gas pipe had pits in it due to the arcing. Checked the outside main panel & found very loose neutral (had used the ground strands from the outer wrapping of SEU cable for the neutral). Tightened wires, problem fixed.
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A 240 volt AC unit would not cause this as it does not put a load on the neutral, the blower motor in the furnace or air handler would though which is what they might have been seeing, as for the range older electric ranges did use the neutral for some of the smaller top burners or when they were set to lower settings, but most today use only the two hots and switch between different elements to control the amount of heat, it sounds like the range only had a 3-wire hookup and was using the neutral for both the EGC and neutral as was allowed in older installations.

The gas pipe must have had a electrical path to another service and would have had to be all metal which is very rare today, because if it was only connected to this houses grounding/neutral it would have been at the same potential of this houses neutral and there would have been no arcs, it could have been through a water heater to the water pipe which would make sense then the water pipe would have made the connection to the street main which is connected to other service neutrals.

I had a house that had a 30 amp 120 volt only service, no 240 volts, the customer had three different electricians out to find out why the cable TV's wire was burning up, at one time it actually caught fire, over time they had put all 30 amp fuses in the 4 space fuse panel so the load was more around 60 amps at times when they were using the microwave and toaster and coffee pot along with everything else in the house, the other electricians didn't have a clue as they told the owner they never ran into something like this, I just shook my head when she told me this and I showed her where a tree limb had fallen and hit the drop pulling the neutral apart leaving the hot still connected, I just used a split bolt to put the neutral back together and all was well, I also told her that the house was in serious need of updating and that having the 30 amp fuses in the panel was a big fire hazard just waiting to happen, but she didn't have much money and I had to go to another job she said she would have her son put 20 amp fuses in it as all the circuits (all 4) were in #12, it's amazing how people survive like this.
 
steve66 said:
So it may or may not be a hazard.

But isn't that why the jumper is usually made long enough to replace the meter without removing the jumper?

IMO The water dept. should not be removing the jumpers without adding a temporary jumper, or without making sure no shock hazard is present.
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Kind of hit some of what I wanted to say there - the jumper is there to bridge the gap when the meter is removed, the water dept technician shouldn't be removing it. If he removes it and then removes the meter, who knows what the open circuit voltage may be between the two remaining pipes.

People installing these jumpers should install them in a way that leaves room to remove the meter, after all they mostly are there to bond across when the meter is not present. I haven't ever seen a meter that wouldn't pass continuity through the piping, but maybe there are some, it is still the missing meter that the jumper is all about IMO.
 
kwired said:
Kind of hit some of what I wanted to say there - the jumper is there to bridge the gap when the meter is removed, the water dept technician shouldn't be removing it. If he removes it and then removes the meter, who knows what the open circuit voltage may be between the two remaining pipes.

People installing these jumpers should install them in a way that leaves room to remove the meter, after all they mostly are there to bond across when the meter is not present. I haven't ever seen a meter that wouldn't pass continuity through the piping, but maybe there are some, it is still the missing meter that the jumper is all about IMO.
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There are some meters that has a yoke that will keep the pipes connected when the meter is removed, these do not have to be jumped out, but then there are the open yoke meters that when the meter is removed there is no continuity between the pipes and a jumper is needed, the ones that has the X frame yoke are the ones that we never jump out, also there is some that have a U looking yoke but doesn't make a really good connection so we also bond them too, then there is the one that just has a union on each pipe end to connect the meter too, these always has to be jumped, of course I'm talking about meters that are located in the house not the street located ones.
 
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