Service neutral impedance

[karl riley]

I have a question to pose about service neutral impedance and voltage changes, but first I have to ask this question:

What percentage of service neutral impedance (or open) problems are slow-developing, and what percentage are sudden?

POCO guys care to give a ball park answer?

Karl

 

[charlie]

Re: Service neutral impedance

Karl, I don't have any idea. However, from my own experience, I would guess that 90 to 95% are slow developing.

 

[brian john]

Re: Service neutral impedance

The ones I've been involved with were appear to be slow in developing , I base this upon thermal evidence and arcing/pitting of the connections.

Have seen several loose neutral connections in the meter stacks utilized in apt complexes. These appear to be assembled with self tapping screws. Due to meter stack design and the loads present IR is very hard to utilize in these stacks, we have utilized ultra sonic listening devices for locating arcing neutrals in stacks with some degree of sucess.

APTS (at least in this area) seem to use the low end of all distribution equipment. Older apt complexes have Zinsco and Bryant, with FPE in the upscale complexes.

 

[karl riley]

Re: Service neutral impedance

OK, that is what I thought: slow developing corrosion or loosening. So that lets me go to my second inquiry.

Background of inquiry: among the EMF community there has been an influential voice that does not want to interrupt the water pipe connection because he says it provides a safety backup in case of an open neutral.

My contention is that the water pipe (to the neighbor's neutral) will simply mask a slowly developing impedance in the neutral.

Without that water pipe "backup" one would start experiencing voltage differences, light bulbs being either dim or bright and blowing out frequently. And so one calls the POCO and they check the neutral connections and clean them up. Problem solved, safety re-established.

With the water pipe backup the corrosion/loosening could proceed to an actual open neutral. Then the water system becomes lethal, and if that system is worked on or changed, the suddenly exposed open neutral would fry equipment, etc.

At that time I had my lab since I was producing gaussmeters. So I made a test set-up on a piece of plywood. Ran two hot legs to two porcelain lamp bases and the same for the neutral. Connected unbalanced loads to the lamp bases, and then tried introducing impedances into the neutral line. I graphed the results and they made smooth curves, but:

Not being an EE, I did not know the mathematical way of calculating voltage differences with varying neutral impedance, so I always wondered how accurate my graph was, since I used DC resistance values for my impedances. So here is my question: can anyone on the forum run the math and check these sample values?:

1 load: 1500 watts, 2nd load 60 watts
neutral impedance 1 ohm; resulting high leg voltage 135V.

Same loads, neutral impedance 4 ohms; high leg voltage 154V.

Same loads, neutral impedance 10 ohms, high leg 184V.

Anyone have that formula?

Karl

 

[dereckbc]

Re: Service neutral impedance

Karl, I know you are smart, so I will give you some hints and let you figure it out.

First convert the loads from watts to ohms using normal operating conditions of 120 volts across each load, assuming a neutral impedance of 0 ohms. You should get something in the neighborhood of 10 and 250 (not exact, figure it out)


Next get a pencil and paper and draw the circuit out and work ohm's law and see what you come up with. I think if you see the mechanics you will get a better understanding.

Dereck

 

[pierre]

Re: Service neutral impedance

Karl

I agree with you a 1000%. The waterpipe connection method should be discontinued and we should have a mandatory rule stating that all new work use the Ufer ground as the primary ground.
That might create a stir.

Pierre

 

[dereckbc]

Re: Service neutral impedance

Karl, there are a few solutions to the grounded circuit conductor problem, most are architectural changes which would require completely rebuilding the current distribution system, not an option.

However there is one simple way to detect the problem, a simple monitor/alarm circuit to alert the owner/user/operator of a degraded neutral circuit. There are several ways to do it. Simplest/cheapest most reliable method is just a balance meter across each leg to neutral.

 

[Guest]

Re: Service neutral impedance

If you read up on Ufer it was designed to be a <5-Ohm grounding system. That would be a vast improvement over the <25-Ohm setup now.

I don't believe any new construction is bonded to the neighbor through the water pipe. First off at each meter there is a "di-electric" union which adds impedance. Secondly, most new site work involves going to plastic before the copper water pipe gets to the meter. Finally, newer water mains are plastic. Conclusion: New or old it's unlikely there is a bond between neighbors. The impedance would be closer to whatever the earth is. [I put di-electric in quotes because they call it a di-electric coupler, but it jibes with my definition of di-electric. Regardless, it is somewhat insulating].

I am open minded about this, so please bring on the constructive rebuttals. I'm an easy target because I'm still getting my legs back. Most folks here have a big leg up on me. I welcome all constructive comments about my postings.

 

[dereckbc]

Re: Service neutral impedance

Originally posted by awwt:
If you read up on Ufer it was designed to be a <5-Ohm grounding system. That would be a vast improvement over the <25-Ohm setup now.

Wayne I am curious why you think a 5 ohm ground is better than a 25 ohm ground.

 

[roger]

Re: Service neutral impedance

awwt,

Conclusion: New or old it's unlikely there is a bond between neighbors.

In your reference to "NEW" you are basically correct.

As far as "OLD", most older urban neighborhoods are common through grounding in the grounded conductor conversation.

Roger

 

[karl riley]

Re: Service neutral impedance

AWWT, no, dielectrics are not installed at the meter. If they are, you have to bond around them.

It is very common that the neutral currents of existing homes are interconnected by way of the water pipes. this is reality, not theory or guessing. I deal with this constantly. EPRI constructed a whole demo subdivision in Mass to study the circulation of neutral current on water pipes between houses in different conditions.

 

[Guest]

Re: Service neutral impedance

Originally posted by dereckbc:

Wayne I am curious why you think a 5 ohm ground is better than a 25 ohm ground.

Less fault tolerance.

 

[Guest]

Re: Service neutral impedance

Originally posted by karl riley:
AWWT, no, dielectrics are not installed at the meter. If they are, you have to bond around them. <snip>

My water company states that their water meter includes a di-electric element. After observing the construction of the meter I can see that even if not true di-electric that it does have some insulating value-- and that would add impedence.

I'll stick my VOM on my water meter later and post back.

 

[karl riley]

Re: Service neutral impedance

Dereck, to get back to what this posting was about, I thank you for assuming that I can do the math. I must have had a math teacher I didn't like in high school.

But I tried, and found something interesting. The two impedances are 9.6 ohms and 240 ohms. When you add the impedance of the neutral that I introduced, as I look at the diagram, some of the current from either load goes through the neutral, and a portion goes through the other load, as part of a 240V circuit. I am confused as to what equations to set up.

So I started more simply. With an open neutral, the two loads are in series in a 240V circuit. OK, so the 240V divided by the total ohms gives you a current of 0.96A. This current times each load's ohms gives the voltage over each load. The 240 ohm load will have 230V across it, and the 9.6 ohm load will have 10V across it.

This accords with my experiment, because as I increased the neutral impedance, the curve of high voltage went up sharply and leveled off: 225V at 60 ohms neutral imp.; 227V at 81 ohms, and 229V at 99 ohms impedance. So at 100 ohms you are as good as open.

But I don't know how to mathematically put in the neutral impedance when the neutral goes to the Tfrmr xo point and the loads are at the same time part of the 240 V circuit. Give me another hint.

Karl

 

[karl riley]

Re: Service neutral impedance

AWWT, whatever you find will add to your understanding. But please do not take the trouble to engage me in a dialogue about this. I am glad that your eyes are being opened here, but spare me.

Karl

 

[Guest]

Re: Service neutral impedance

Originally posted by karl riley:
<snip>I am glad that your eyes are being opened here, but spare me. Karl

Karl,
My eyes are being opened further every day. They are not closed, but I don't know everything. That's life. As for water meters I am only adding what I have been told by my water company, what I have observed, and what I believe.

There seems to be a deeper issue here between you and me, but I can only act on what I know, and I can only relay what I believe. Work with me here.

I just sent you a PM just before reading this latest comment from you, so please be aware that anything in that PM is not colored or in response to this latest posting of yours.

>>>
[Post addendum 6:30PM PST-- original post above 6:00PM PST].

OK. Here we go. First off Karl, I want to know that I have the highest regard for your field of expertise. I also have the highest regard for your postings (except the ones where you get personal with me ). I want you to like and respect me, but that's your decision to make.

My eyes were opened in reverse. I too for my younger years assumed and was told that a water pipe ground was the best ground and that everybody was bonded in a neighborhood (back then it was all metal piping).

I assumed that in a metal piping system that everybody was bonded together and that a metal water pipe ground went for miles. Not that miles were needed but I was confident that the bond passed through the meter.

Somewhere in my electrical career my water company alerted me to the fact that the bond cannot be relied on past the meter as the meter includes a di-electric component. This is what they told me. It was news to me, and yes my eyes were opened. I never verified it. I just relied on the fact that they were from the government and they were there to help me and their word was gospel. I had no reason to question or verify their statement, nor did I want that liability.

This thread started by you brought up the neighborhood bonding issue again. I responded with my personal knowledge and what I believed to be the truth. I did not call you a liar or say your statement was false. I said "I don't believe..." because that's a correct statement based on what I know.

In the past 30-minutes I have sent you a PM, and I also as promised went out and uncovered my water meter (I actually had started that project today-- so this just spurred me on to finish the job. The moles had filled it in and I like to clear it out so my meter gets read properly. The moles make it easy to clear out-- the dirt is already loose).

RESULTS: I isolated the meter from the earth. FYI: I'm on an all metal system in an older neighborhood. The metal inlet and outlet from the meter still go into the earth but I got the meter and the connectors and valves to float in mid-air. I put my VOM on it and was expecting a high impedance. Actually, there was NO effective continuity between the street side of the meter and the house side of the meter. I did not expect this. I thought there would be some significant continuity. Of course with better equipment there has to be some impedance because as Bennie has stated "there is no perfect insulator". It turns out this water meter is a very good insulator from my house to the main.

I am hoping this information can be received in the manner it is intended. I am trying to add to this thread. I am not trying to divert attention. The question was broached. This is my answer. I am not trying to prove anybody wrong. I am only trying to verify my belief.

Personal note to Karl: I would love to hire you to do an EMF check of my home (and a continuity check of my water meter) as your talents, experience, and equipment surpass mine. I am not the brightest bulb here by far. I do bring something to the table, and I hope you can find a good portion of my input useful.

That's it for now. I hope it makes sense, and I hope it is not found to be confrontational, or diversionary as that is not my intent. Peace. It's dinner time. Bye.

[ September 20, 2003, 10:38 PM: Message edited by: awwt ]

 

[karl riley]

Re: Service neutral impedance

NEC requires you to use your metal water pipe as a grounding electrode. If your water meter is at your house and a dielectric has been inserted in the meter, NEC requires that you bond around it to maintain continuity. Your house may be in violation.

 

[dereckbc]

Re: Service neutral impedance

Originally posted by karl riley:
Dereck give me another hint.

Karl

Voltage divider circuit (ratio).

Here is another hint. With a neutral impedance of 4 ohms your voltage drop across your 9.6 ohm load would be 13.6 volts, and the 240 ohm load voltage drop would be 226.4 volts

 

[Guest]

Re: Service neutral impedance

Originally posted by karl riley:
NEC requires you to use your metal water pipe as a grounding electrode. If your water meter is at your house and a dielectric has been inserted in the meter, NEC requires that you bond around it to maintain continuity. Your house may be in violation.

1. The high-impedance water meter is forty-feet from where my water service enters my dwelling.

2. There is no separate di-electric union on my house or on the meter (except at the water heater connections-- which are properly bonded).

3. Starting at the meter my water supply and heading towards my house the water pipe goes brass, copper, brass, copper. There is no iron so no need for a di-electric union.

4. The water meter itself, according to the water company has di-electric components. Earlier this evening I confirmed this. There is no code violation per UBC or NEC. Since they told me about the di-electric properties I have never verified it until today. That was many, many years ago.

My hope is that you will be open-minded enough to accept this and add it to your bag of tricks. If not, then hopefully somebody reading this will benefit from knowing that their water meter may have a degree of insulating property.

It is my opinion that the reason we discuss these things out in the open in a forum is for the benefit of everybody who reads it, not just those that start a thread or those that reply to a thread. It's a fabulous thing to allow a brain trust like this to exist. Ten years ago we would have been left mostly to our own beliefs.

Again, I did not start this portion of this thread but am only responding with that which I believe to be true.

Portions of this discussion would be better served by Private Messaging.