Water pipes as neutral backup

[karl riley]

When metallic water systems exist, the required grounding to the pipe allows some neutral current to return to the transformer through a neighbor's neutral and vice versa. For different reasons this current on the water system can be considered objectionable.

It is sometimes stated that this connection is good because it provides a backup for the neutral if the service neutral opens. Can anyone offer reasons why this is good? Since I can see many disadvantages to using water pipes as backup, I want to be aware of the other side of the question.

The disadvantages as I see it are:
1)it masks a dangerous situation (open neutral) that needs to be fixed as soon as possible.
2) It puts current on conductors which were not designed to carry current and hence are unregulated by NEC specs.
3) It sets up a lethal situation for any plumber or water worker who separates a pipe carrying the return neutral (120V).
4) It causes high magnetic fields both from the pipes and both service drops.
5) The widespread use of plastic water pipes has not been connected with any safety issues I have heard about.

So now, how about the pro arguments. Anyone?
Karl

 

[bennie]

Re: Water pipes as neutral backup

Everyone corrects me when I say the 5 foot rule, for connecting to the water pipe, was to prevent magnetic fields from appearing through out the house.

Using the magnetic field issue, is considered a design issue and suggestion of problems with EMF's.

Using the safety concept of the possibility of replacing the metal pipe with plastic to substantiate the code rule made it fly through without getting into the controversy surrounding EMF problems.

The loss of the water pipe as a ground electrode is already covered in two other code sections. Bond around non-conductive joints, and the supplemental rod requirement.

Where have you seen three code sections to correct or prevent the same thing?

[ May 17, 2003, 02:20 PM: Message edited by: bennie ]

 

[bennie]

Re: Water pipes as neutral backup

Karl: I know of two incidents where replacing the water service with plastic has caused damage to equipment. One was my neighbor, when I replaced my electric service, and water pipe. One TV got zapped.

The other was a young girl college student with a new computer. The computer smoked when the water company shut off the water to replace a leaking pipe.

Both cases the neutrals had been broken for some time.

 

[karl riley]

Re: Water pipes as neutral backup

Bennie, the two examples you give show that a bad neutral connection had been masked by the water pipe backup which used the neighbor's neutral. By the time the water pipe path was interrupted the neutral connection was bad enough to cause enough voltage imbalance to smoke a device. Agree?

So the question is, was this masking of a developinbg problem a good thing or did it cause more damage. As a neutral connection gets worse, the first symptoms are annoying but not damaging, like dim or extra-bright light bulbs, etc. The occupant complains to the utility and they come out, test the system, and go clean the neutral connections. So wasn't the water pipe backup a bad idea for masking these symptoms?

As far as your first post, I could not understand some of your sentences. Could you re-state?
Thanks, Karl

 

[bennie]

Re: Water pipes as neutral backup

Karl: The water, gas, and cast iron sewer pipe, was used and intended to act as a safety valve for the neutral of the Edison three wire system.
This is why a larger conductor than on an artificial made electrode.

Service drops were separate conductors in the old days. A storm breaking two of the conductors would likely get the neutral. Without the water pipe connection, the panel cover would reach 120 volts.

People were going outside barefooted to check the fuses and getting killed when touching the panel. One case both the man and his wife were killed when she went out to see what was wrong and tried to turn on a light.

 

[Ed MacLaren]

Re: Water pipes as neutral backup

The water, gas, and cast iron sewer pipe, was used and intended to act as a safety valve for the neutral of the Edison three wire system

Bennie, this is all news to me. I guess we had a serious safety problem at home when I was a kid. We had a hand pump, an outhouse, and cooked on a woodstove.

But then, come to think of it, we didn't have electric power either.

Ed

 

[dereckbc]

Re: Water pipes as neutral backup

Karl this is an interesting discussion for which there is no right answer. Using a metallic water pipe has the advantage of backing up the neutral in the event the neutral should ever fail. But in most residential installations there is no way to detect an open neutral unless there is some means to detect it, or is periodically checked. Perhaps some observant consumer might notice a difference, but not likely. Then comes the plumber and finds it the hard way.

The other side is using a plastic water pipe. Life is good until a problem happens like a storm comes and opens the neutral, the voltage is unbalanced, and pop goes the TV and VCR. Or it could degrade as you said, and the consumer may or may not notice a dimming and bright light. Who knows?

There are some solutions, but not likely to ever be implemented in a residential setting. For instance lets say the utility supplies the EGC from the service transformer. Not likely, the NESC and NEC will not have any part of it. However this is done in some commercial and industrial environments where the facility owns the transformer.

Another approach would be to use a different architecture, say something like a delta/delta or balanced power system that does not use grounded circuit conductors. Again this is not likely for residential, it would raise equipment cost. Again, it is applicable for commercial or industrial.

So what is the answer? Beats me, darned if you do, darned if you don?t?. Dereck

 

[hurk27]

Re: Water pipes as neutral backup

what if we had 4 wires comming from the pole.
2 hots 1 insulated neutral and a bare ground wire.
this would keep the shared paths on the poles where they belong and would also make it harder for the contact of a primary conductor to the neutral. then the ground rod would only be for lightning strikes.
As far as the problem of loosing the neutral a shunt trip main with a relay between the neutral and ground would trip the main and prevent damage to appliances and maybe even a house fire or two. with the neutral bonded at the pole only. there would be no stray current on the grounding conductors. and no EMF in the house.

 

[bennie]

Re: Water pipes as neutral backup

Remedy when metal pipes go away.

Surfaces under panels to be non-conductive.

Appliances to be double insulated. No ground wire.

Loss of neutral indicator.

 

[karl riley]

Re: Water pipes as neutral backup

Thanks all for some very good points (and a warning about going out to check the power in bare feet in a rain storm).

Another thought for the future: a doughnut coil around the service conductors would detect the net current when neutral is being shunted to water pipe. It could be set to operate a warning device at some predetermined amperage. I believe these are available as stock items for commercial use.

As things stand now, I still am of the opinion that the undesigned, unregulated water pipe "backup" which includes unauthorized use of the neighbor's neutral does more potential harm by masking a developing neutral problem, including zapping (maybe killing) water workers.

But I would like to hear from anyone else who sees a benefit to this kind of backup which might override the dangers.
Karl

 

[bennie]

Re: Water pipes as neutral backup

We will know how many accidents were prevented by observing the ones created, when the metal water pipes go away.

A static sensor, on the panel covers will save lives.