Open neutral

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peter d

peter d

Senior Member
Location
New England
I had an open neutral situation last month that baffled me a bit.

The open neutral itself happened when the triplex going to the house snapped at an intermediate pole due to years of tree limb chafing (branch grew into the drop, stressed it, and finally the messenger snapped from fatigue.)

Anyway, the house was a typical rural situation. No metal water main and no gas line. The only connection to earth was 2 driven ground rods. The only possible other connection to earth was the EGC via the well pump, but I never checked to see if the EGC was bonded to the well casing or not.

So the symptoms were typical open neutral behavior. Lights dimming and brightening, fans running fast and slow, UPS on the computer kept kicking on and off, etc. I took voltage readings and they never fluctuated too wildly as I would have expected them to, and not enough to fry any electronic equipment. There was 4 amps of current on the GEC at one point when I took a measurement.

Also, keep in mind this went on for over a week with the messenger completely snapped. The only connection back to the poco transformer via the earth was via the ground rods and possibly the well casing. No equipment in the house was fried, though I'm guessing the UPS might have saved the computer.

So, it begs the question. I never thought that ground rods alone could stabilize the voltage enough to prevent catastrophic changes in voltage. Now I'm thinking they can. :confused:
 
peter d said:
I had an open neutral situation last month that baffled me a bit.

The open neutral itself happened when the triplex going to the house snapped at an intermediate pole due to years of tree limb chafing (branch grew into the drop, stressed it, and finally the messenger snapped from fatigue.)

Anyway, the house was a typical rural situation. No metal water main and no gas line. The only connection to earth was 2 driven ground rods. The only possible other connection to earth was the EGC via the well pump, but I never checked to see if the EGC was bonded to the well casing or not.

So the symptoms were typical open neutral behavior. Lights dimming and brightening, fans running fast and slow, UPS on the computer kept kicking on and off, etc. I took voltage readings and they never fluctuated too wildly as I would have expected them to, and not enough to fry any electronic equipment. There was 4 amps of current on the GEC at one point when I took a measurement.

Also, keep in mind this went on for over a week with the messenger completely snapped. The only connection back to the poco transformer via the earth was via the ground rods and possibly the well casing. No equipment in the house was fried, though I'm guessing the UPS might have saved the computer.

So, it begs the question. I never thought that ground rods alone could stabilize the voltage enough to prevent catastrophic changes in voltage. Now I'm thinking they can. :confused:
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You likely (and luckily) had a fairly balanced load.
 
I had a call on one several years ago that took me a bit till i located it. Same situation where a tree finally did in the neutral. This lady had major damage. Unless dealt with fast the damage will happen. If anyone had Mike Holts vcr tapes in 96 for the masters there was a part where a duplex caught fire from loss of poco neutral. Was metal lath over wood frame. The unit that caught fire was emty at time. Years of current going thu the metal lath turned the plywood into charcoal till it flashed over.
Point here is many things will try to act as the neutral return. Everything from ground rods, copper lines in slab,pipe to water meter or gas,well casings and even swimming pools.
Often our unbalanced loads are very low so with help from the above you might keep the lines at a somewhat safe voltage of maybe 90 to 150 volts on a normal 120 / 240 service.
Important thing is when on calls like this do not add damage by turning things on and off. With a call like this your best off to pull panel cover and check voltage. If unbalanced by several volts kill the main fast and locate the open.
 
LarryFine said:
Compare the neutral current now (repaired) to that 4a.
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Thats what I was thinking, if the unbalance current were to get much over that there would have been serious voltage problems.


Now I have seen where a homeowner had enough surge protectors in his house it did force the neutral to a point close to balance, but he was still getting fluctuations, it was strange because it wasn't till we started turning off breakers did it start varying at a much greater rate, well after all was said and done, we figured it out, every room in his house had two or three plug in TVSS strips, and as we were turning off the breakers we were removing those TVSS strips from the service connection.

I am now a firm believer in never having to many.
 
hurk27 said:
. . . it wasn't till we started turning off breakers did it start varying at a much greater rate . . .
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I believe it was removing the line-to-neutral loads, and not the surge suppression, that increased the voltage variations. The more loads you have on, the more likely the neutral voltage will hover near zero.
 
My guess would be that there was enough moisture in the tree and that the two ends of the line weren't more than a 1/4 inch or less apart.

I've lost neutrals with no damage occuring and I've lost legs with lots of damage.

Like I was told once when I asked for an explination of what happened, "it's electricity, it does what it wants.":)
 
cowboyjwc said:
My guess would be that there was enough moisture in the tree and that the two ends of the line weren't more than a 1/4 inch or less apart.

I've lost neutrals with no damage occuring and I've lost legs with lots of damage.

Like I was told once when I asked for an explination of what happened, "it's electricity, it does what it wants.":)
Click to expand...

Your partly right. Sort of like computers, they do what there told to do. Garbage in = garbage out.
When we remove a nuetral we create a differant circuit from what we had. The circuits are like resisters resisters in parallel and in series. If we have 2 light bulbs of 100 watts each and 1 is on side A and other side B and are no other loads we could cut the neutral and nothing happens. Do the same with a 25 watt bulb and a 100 watt bulb and you will burn up the 25 watt bulb in split second.
If you go to your panel and turn on or off loads till you have zero amps on neutral then there will be no damage if you remove neutral.
Electrical circuits do exactly as they should for what they are at any given second.
Not always easy for many to understand. If you have an electronics background it helps.

How much damage is created is just a matter of what loads were on. Problem is home owner will not call till after they spent an hour being confused as to what works or doesnt work. After they see some bulbs flash or some smoke from appliances they then call you assuming phone still works. I have seen damage to the tune of thousands. I highly suggest you put all your electronics from TV , computers, printers, clocks on a UPS box. They cost from $50 to a few hundred for the ones you need in your house or home office.
 
Jim W in Tampa said:
I highly suggest you put all your electronics from TV , computers, printers, clocks on a UPS box.
Click to expand...

I agree (except for clocks). I have a few at home. A lot of stuff these days I fortunately rated for 90 to 240V and those item usually are okay.

One morning I turned on the toaster and the kitchen lights got brighter. I immediately went and killed the main breaker and power company came out in less than an hour after calling. No damage

Funny thing, customer service rep told me to first try turning off all breakers and then on again. I told her I wouldn,t as she had no idea what a neutral was and didn't know if it was better lost or found. She said my power wouldn't be on if the breakers were off. gee, thanks, lady!
 
Jim W in Tampa said:
Your partly right. Sort of like computers, they do what there told to do. Garbage in = garbage out.
When we remove a nuetral we create a differant circuit from what we had. The circuits are like resisters resisters in parallel and in series. If we have 2 light bulbs of 100 watts each and 1 is on side A and other side B and are no other loads we could cut the neutral and nothing happens. Do the same with a 25 watt bulb and a 100 watt bulb and you will burn up the 25 watt bulb in split second.
If you go to your panel and turn on or off loads till you have zero amps on neutral then there will be no damage if you remove neutral.
Electrical circuits do exactly as they should for what they are at any given second.
Not always easy for many to understand. If you have an electronics background it helps.

How much damage is created is just a matter of what loads were on. Problem is home owner will not call till after they spent an hour being confused as to what works or doesnt work. After they see some bulbs flash or some smoke from appliances they then call you assuming phone still works. I have seen damage to the tune of thousands. I highly suggest you put all your electronics from TV , computers, printers, clocks on a UPS box. They cost from $50 to a few hundred for the ones you need in your house or home office.
Click to expand...

That is correct. Most us us just need to hear the problems and we know right away what it is, we just have to find it.

Had a high voltage transmission line break and fall on the lower part of the pole and land on the utility ground wire. The pole fed four houses. One house the meter blew off and was about 10' from the panel with no damage to anything in the house. The second house had a brand new service and all of the required grounding. In that one all of the electronics blew and on a piece of EMT there was an arc mark every where there was a strap. The other two houses, nothing. Why? That's where I heard the line about it doing what it wants.
 
You might have had a good grounding potential between ground rods with well casing at the house, and ground rod at the base of pole where the transformer is located. All the 120v stuff was working at a lower voltage but not low enough so the equipment would stop working.
 
cowboyjwc said:
My guess would be that there was enough moisture in the tree and that the two ends of the line weren't more than a 1/4 inch or less apart.
Click to expand...

The messenger was intact until they had the tree trimmed that was chafing the triplex. ;) Once the branch was gone, it relaxed the messenger and it snapped clean apart at the weak spot. There was no poco neutral connection left to the house whatsoever.
 
peter d said:
The messenger was intact until they had the tree trimmed that was chafing the triplex. ;) Once the branch was gone, it relaxed the messenger and it snapped clean apart at the weak spot. There was no poco neutral connection left to the house whatsoever.
Click to expand...

Ahh, the reason I brought it up was I had the same thing happen only the line was running right through the limb which had grown around the wire and it was one of the hots. When the wind would blow it would give them fits. Finally the limb just stretched the line apart and that's when they called me.:)
 
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