High impedance neutral?

C

CaliforniaMikeH

Member
Location
Columbus Ohio
Occupation
Electrical Engineer
Hey all,
This is a personal one, and I usually post over on Elsmar cove in Med Devices. However, I am stuck between my local power company and my internet provider and would appreciate any help/suggestions.

I bought a new house. About a year in, my internet went out. (Cable) during the repair, it was found that the connection to the cable from the pole was a badly melted. However, they repaired it and suggested that I get the local power company to confirm my connections to the pole. I had them come out and they left a message saying that the connections were fine, but that I did not have a ground rod system and that I probably have a grounding/neutral issue in my house. Sure enough, when I go looking, I only have a old water ground, though there is evidence that there used to be a ground rod.

So, talk to city, put in ground rods, and do a few checks before I tie it in.

Place current clamp around internet cable and meter reads 2.5 A AC

Measure the voltage between the cable shield and the new GES 1.00 VAC

Disconnect internet cable and ground from house...

Voltage between internet shield and new ground rod system is 0.45 VAC

Voltage between house ground and new GES 2.58 VAC.

Voltage between house ground and cable shield is 3.80 VAC.

Set meter to measure AC current and put probes between internet shield to pole and house ground and the meter reports 2.5 A AC

Place probes between house ground and new GES and meter reports 200 mA AC.

My interpretation is that the internet modem on the pole has a better neutral connection than my house, that this is driving the local ground potential up several volts, and that local power company needs to fix my neutral connection to the pole, and that if it gets much worse, things could get exciting. Local power company says internet company needs to fix their modem.

Am I nuts?
 
CaliforniaMikeH said:
I had them come out and they left a message saying that the connections were fine, but that I did not have a ground rod system and that I probably have a grounding/neutral issue in my house. Sure enough, when I go looking, I only have a old water ground, though there is evidence that there used to be a ground rod.
Click to expand...
A ground rod or lack thereof should not be a problem. The system should operate normally without a ground rod and you already have a water pipe electrode. Did you check the main bonding jumper at the service? Have you checked all of the neutral connections?
 
First, thanks all. Greatly appreciated. Especially in 10 minutes.

Voltage between the neutral coming into the service and the service ground is several mv AC.

I just put my clamp around the line from the pole and it reads a net current of 2 A AC. Current to cold water pipe read 50 mA. Turned off main breaker and net current dropped to 20 mA AC.

I'm thinking neutral connection at pole.

???
 
I've never seen a "modem" on the pole.

I need to know the current on each of your hots as well as on the neutral where they come into your panel. Then I want to see the current on your cable drop and the current on the GEC going to the water line. I don't care about any voltages or the ground rods.

Do you have a "ground block" that the cable drop connects to outside or inside near where the cable drop enters your house? There should be a ground wire from it connected to the panel with a clamp or maybe to the GEC going to the water line. The ground block grounds the cable shield to your service neutral. The cable company is required to provide all that.

Essentially you have three parallel ground paths throughout your neighborhood that connects all houses together:

The power company neutral from house to house.
The cable company shields from house to house.
The underground water line from house to house.

It's entirely possible that what you are seeing is the division of current among the three paths coming from outside your house. I also suspect that the melted cable on the pole might be from lightning or a power line fault at one time. I would certainly have your neutral and connections checked at the panel, at the meter and at the pole. Other than that, I would just pay attention for any flickering lights or a drastic increase in current on the cable drop.

-Hal
 
Hal et al,
First, thanks for the help.
Second, sorry for the slow reply. Life got a bit complicated for a few days.

Unfortunately, the neutral from the service is routed behind all of the branch circuits. To gain access for a clamp, I would need to tear the panel wiring all to heck.

That said, if I clamp the entire service (both legs and neutral) I get 2.2 Amps. To my mind, this should be close to zero and represents the current not returning on the service neutral. Looking at the cable company ground, I had 1.8 Amps. The cold water ground had 0.4 Amps. I then checked the service to confirm that the house load was stable and it was still showing a lost 1.8 Amps.

Leg 1 was carrying 4.3 Amps
Leg 2 was carrying1.5 Amps.

I think...
(Please tell me if I am off in the weeds)

Voltage across neutral landing in the panel is essentially zero (<20 mV) and there is no evidence of damage or heat. The same holds at the meter. This tells me that the landings at these points are solid.

1.8 Amps (cable ground) + 0.4 Amps (water ground) = 2.2 Amps (lost current on service) so I think I have a pretty clear picture of the cable ground carrying 1.8 Amps back to the pole. Also, I would expect a neutral current of about 4.3 Amps(leg 1) - 1.5 Amps (leg 2) = 2.8 Amps, and most of this is headed to the cable company.

I think this points to a high impedance neutral connection at the pole.

Does this make sense?

Should I be concerned and get the power company in to check at the pole?
 
CaliforniaMikeH said:
Hal et al,
First, thanks for the help.
Second, sorry for the slow reply. Life got a bit complicated for a few days.

Unfortunately, the neutral from the service is routed behind all of the branch circuits. To gain access for a clamp, I would need to tear the panel wiring all to heck.

That said, if I clamp the entire service (both legs and neutral) I get 2.2 Amps. To my mind, this should be close to zero and represents the current not returning on the service neutral. Looking at the cable company ground, I had 1.8 Amps. The cold water ground had 0.4 Amps. I then checked the service to confirm that the house load was stable and it was still showing a lost 1.8 Amps.

Leg 1 was carrying 4.3 Amps
Leg 2 was carrying1.5 Amps.

I think...
(Please tell me if I am off in the weeds)

Voltage across neutral landing in the panel is essentially zero (<20 mV) and there is no evidence of damage or heat. The same holds at the meter. This tells me that the landings at these points are solid.

1.8 Amps (cable ground) + 0.4 Amps (water ground) = 2.2 Amps (lost current on service) so I think I have a pretty clear picture of the cable ground carrying 1.8 Amps back to the pole. Also, I would expect a neutral current of about 4.3 Amps(leg 1) - 1.5 Amps (leg 2) = 2.8 Amps, and most of this is headed to the cable company.

I think this points to a high impedance neutral connection at the pole.

Does this make sense?

Should I be concerned and get the power company in to check at the pole?
Click to expand...
All of your neutral current is flowing on a path other than the service neutral. This needed to be fixed as soon as possible. From the information you have provide the service neutral has a problem on the line side of your service panel. It could be in the meter or at the pole. If your power company is good they will have beast of burden tester that they will plug in in place of the meter. That tester will show if the service neutral is compromised anywhere between the transformer connection up to and including the line side connection at the meter.
 
don_resqcapt19 said:
All of your neutral current is flowing on a path other than the service neutral. This needed to be fixed as soon as possible. From the information you have provide the service neutral has a problem on the line side of your service panel. It could be in the meter or at the pole. If your power company is good they will have beast of burden tester that they will plug in in place of the meter. That tester will show if the service neutral is compromised anywhere between the transformer connection up to and including the line side connection at the meter.
Click to expand...
Even with this they miss bad neutrals a lot of the time— had them come out twice to several jobs because of this
 
How can you not think it’s possible
depends on how bad connections is- wind come up and connections swings back and forth and now it’s not in the same location and not making as good as contact.- happened a lot around here- they come back second time- can’t find anything go up and recrimp connection and then all gone.
There is one guy that retired and just recrimped regardless when he came- he only came Once every time- told me easier that two visits
 
Thanks again everyone.

To add to this, when I saw the melted cable ground and measured current on it, I had the power company check the neutral. They said it was fine. This will be my second call to them.
 
CaliforniaMikeH said:
They said it was fine. This will be my second call to them.
Click to expand...
This is a typical response. They often come to check your service in the middle of the day when electricity use is low and might not even use any voltmeters.
This is why they need to use something like the "beast" mention by Don in post #7.
 
One common reason a weak (service) neutral is missed on the first POCO "visit" is the lineman will pull the meter, measure voltages of, for example, 120V L1-N, 120V L2-N and 240V L1-L2. Then declare it's all good on their end, and head out. I get it, it's an easy mistake when you want to close a ticket as fast as possible and drive to the next trouble call.

But when they pull the meter, they obviously stop all current flowing on the service, and it's current flowing on the neutral that cause the problem! So no current flow means no voltage drop across whatever weak neutral crimp or lug, and nothing "bad" shows up.

That's why Don mentioned The Beast above. It gets inserted into the meter socket and can place a decent single phase load across either side of the service. It detects weak neutrals and hots. But it has to be on the truck and the lineman has to be clued in about it's use.
 
All that beast is an extremely high load piece of equipment. This does not do any power analysisor anything like that so at the time of that connection is still making decent contacts. It will say it’s fine I live at the coast where things corrode with high wind just relying on that beast does not do it.
 
If you load one leg, with a 120V load like a hair dryer or space heater, does the voltage between the other leg and neutral go up?. BTW, it's best to perform the test with every other load in the house shut off.

If so you need to look ay all your neutral connections starting at the transformer secondary at the pole, the meter socket, and at your panel.

Although if I understand you right, and you amp clamped all your service entrance conductors, and it showed current, the problem may be a neighbor's service that has a high impedance neutral, and it's due to something shared, like water service, or even the cable system if it's wired and not fiber
 
AC\DC said:
All that beast is an extremely high load piece of equipment. This does not do any power analysisor anything like that so at the time of that connection is still making decent contacts. It will say it’s fine I live at the coast where things corrode with high wind just relying on that beast does not do it.
Click to expand...
It does not take much of compromise on the neutral to show a voltage change when they use the high load of a beast. It is unlikely a connection that changes with the wind is not compromised enough to show up with that tester, However the utility service person may ignore a small voltage change from a slightly compromised neutral.
 
I won’t argue with you cause you’re a lot smarter than me— just speaking from experience maybe my lineman was smoking the green
 
Hey all,
First, thanks again for all of the help. It was very helpful to get some backup and a sanity check.

Next, sorry for yet another delayed replay. It was a bit of a drama, but it is finally sorted out.

It ended up taking 4 visits from the power department before they believed/admitted there was a problem and pulled a new service. The fourth time they came to test, I ended up taking the day off and meeting them at the meter. The basic "you have 122 on both legs relative to neutral" kept being taken as a "service ok" diagnosis. It still sort of baffles me that that none of the first three people that they sent out could grasp that the issue was not voltage, but that the neutral was high impedance. Ended up using a microwave and not a hair dryer, but basically the same idea, and the voltage drop was pretty substantial, especially when I disconnected the cable... When they did take down the old service, the neutral basically fell apart. Turns out that squirrels were gnawing on it from a tree about 1/2 of the way to the pole to the pole, and all of the wires were chewed through at some point, just not at the same point. All that was holding it together was the twist and friction.

Current to the cable shield went from 2.5 Amps to 0.1 Amps.

Thanks again for the help,

Mike

P.S. Turns out my dog is right. Squirrels are evil. She knew it all along...
 
You must log in or register to reply here.
Top