High Neutral to Ground Voltage, Low Hot to Ground Voltage

[aaronoraa]

My house is about 60 yards away from 345 KV high tension lines. I have had some issues with exterior lights that are on motion sensors intermittently failing to come on with moving objects directly in front of them, and must be turned off and powered back on before working again. I would have assumed the unit was at fault except it's happening on both front and rear outside fixtures from different manufacturers (BTW, I don't care about solving the fixture issue), so I tested my outlets today and have

Hot to Neutral - 120.1 volts

Hot to Ground - 62.7 volts

Neutral to Ground - 50.6 volts

Out of interest, I took a large inductor (1000 ft spool CAT-5, pairs end to end series/4000 ft coil length) and from either side of the coil I measure in my living room

Coil to Ground - 22.2 volts

Coil to Neutral - 2.1 volts

Coil to Hot - 54.3 volts

If I open my back door and put the coil on my grass, 6 feet away from where it was in my kitchen, the voltages are higher (other than neutral)

Coil to Ground - 34.6 volts

Coil to Neutral - 0.4 volts

Coil to Hot - 80.6 volts

I found it interesting that the coil to ground voltage was highest when the coil was laying horizontal (parallel to the ground) and went down when arranged vertically. In the vertical arrangement the voltage was not significantly higher whether the coil was oriented parallel to the high tension lines (19.2 v) or perpendicular (19 v). I also found it interesting that the voltage would immediately begin to smoothly drop when the coil was lifted off the ground in relation to height (with the coil kept in the same orientation).

Same location as the prior measurements on the grass, at 5.5 feet elevation

Coil to Ground - 18.2 volts

Coil to Neutral - 0.4 volts

Coil to Hot - 40.1 volts

The coil measurements were the same between the outlet near my back door, used for all above figures, or an extension cord running to the other side of my house (with the coil kept in the same place).

Any thoughts on all of this?

 

[roger]

Note to all, Let's keep the discussion to the theory of what might be the reason and not how to go about fixing it.

Thanks

Roger

 

[mbrooke]

You either have an open neutral at a sub panel, an open neutral at the house, the utility has a stray voltage issue or you are very, very close to that line.


Im curious what you will read if you drive 2 ground rods 12 ft apart next to the side of the house that's facing the transmission line.

 

[ptonsparky]

You are using a high impedance meter and you have an EG that is not connected to the Neutral at the SE.

Voltage on the coil of wire should be expected. Put a load on it and measure again.

We had a several hundred foot run of shielded wire stretched out under some 34.5?? that would throw an arch. Hurt too.

 

[ActionDave]

My house is about 60 yards away from 345 KV high tension lines. I have had some issues with exterior lights that are on motion sensors intermittently failing to come on with moving objects directly in front of them, and must be turned off and powered back on before working again. I would have assumed the unit was at fault except it's happening on both front and rear outside fixtures from different manufacturers (BTW, I don't care about solving the fixture issue), so I tested my outlets today and have

Hot to Neutral - 120.1 volts

Hot to Ground - 62.7 volts

Neutral to Ground - 50.6 volts........


Any thoughts on all of this?

These are the only measurements that have any value. As our fine member from Nebraska said it is a bad Equipment Ground Conductor (ECG) somewhere.

 

[gar]

140420-1341 EDT

aaronoraa:

As a first assumption I do not believe that the 345 V transmission line has anything to do with your problem.

I believe you have a neutral problem somewhere between the interior neutral conection in your pole transformer and within your home. I like using a high impedance meter voltmeter, others do not. If a lower impedance load is needed, then add a 100 W incandescent bulb in parallel, and if more load is needed use a small portable 1500 watt heater that is about 1300 W actually.

Your CAT 5 coil of wire is of little value other than to serve as the plate of a capacitor. A 2 ft square sheet of aluminum would do about the same. If I wanted an inductive pickup coil to sense magnetic fileld intensity, then I want several thousand turns of small wire on a 1/2" square core with the core ends connected to the voltmeter. Readings will be in microvolts to millivolts. Also should use a shunt capacitor to resonant the coil at 60 Hz.

A large single turn rectangular coil about 8 ft by 40 ft below primary wires of a three phase system will probably ready millivolts.

As mentioned above two screwdrivers placed 12 ft apart in the ground may under normal circumstance show a few millivolts to around 100 mV difference. The orientation of the two points with the same spacing may show you the direction of current flow in the earth. Normally this ground current voltage tends to fluctuate somewhat due to all the differences of ground currents.


If you are near to where there is a break in the neutral path, then there can be a considerable voltage difference over a short distance. Be careful.

First, see if you have a ground rod associated with the main panel, or if it is only a water pipe ground, use which ever as one measurement point.

From the ground rod reference what is the voltage to neutral at a receptacle near the main panel. Probably should be less than 1 volt normally. Your measurements indicate some thing much larger. Next connect a 120 V 1500 W heater in some circuit. How much change in the ground rod to neutral occurs. If the neutral to ground bond at the main panel is good, then there should not be much voltage difference from the ground rod to the neutral.

Assume the neutral to ground bond is good, then put a screwdriver probe in the earth about 20 to 40 ft from the ground rod. Measure the voltage difference. First place the probe in line with the ground rod and the pole transformer. Then pick a location perpendicular to that orientation.

After you run these tests, then someone else or I will comment on further tests.

.

 

[gar]

140421-2059 EDT

aaronoraa:

I will assume your supply is 120-0-120 meaning you have a 240 V secondary center tapped. The center tap is your neutral. This should be connected to a power company ground rod at the transformer location.

You should have two hots at your main panel, and the voltage difference between them should be about 240. You should check this measurement. Since you measure 120 from one hot to neutral, then assuming hot to hot is about 240 you should read about 120 from the other hot to neutral. If you get these measurements, then your neutral to ground (earth) is not properly bonded. Or there is high resistance and some moderate current flow into the earth.

Thus, you need to make some useful measurements from neutral to various earth points.

Measurements from my yard. Background first.

The primary supply on my poles can be classified as a floating delta, but probably grounded at the substation. Thus, there is no major primary side neutral current in my neighborhood. The substation is about 3/4 mile away.

I presently have a 50 kVA transformer that supplies one neighbor and myself. There is a ground rod at the pole transformer. About 100 ft of wire runs from the transformer to a pole where my transformer was previously located until it leaked and had to be replaced. From second pole the service branches to my neighbor and to me. The line length is 25 ft or so down the pole and underground about 40 ft to the end of my home, back up about 8 ft to my meter, and down again into the basement and main panel. The water meter is within a few feet of the main panel. The gas line enters in the same area. The water meter is fed with about 150 ft of 1.25" copper pipe. The supply gas line is also copper. The only earthing at the main panel is to the 1.25" water line on the street side of the water meter. In other words an extremely good ground rod.

First measurements were from hose bib on back side of home to transformer pole transformer ground rod. My total load was about 1.6 kW with no cycling load. Degree of balance unknown. Some sample voltages were:
0.130, 0.162, 0.162, 0.162, 0.136.
Next added a 1500 W heater load on one phase.
0.139, 0.118, 0.114, 0.137.
Thus, the change from the approx 10 A load is either about 0.02 or 0.28 V since I don't know the phase.

Change the load change to the other phase and the voltage change is about 0.17 V.

Next while one meter lead was still connected to the pole ground rod I measured the voltage to a probe (screwdriver) 12 ft away and the drop was 0.11 to 0.12 V. Moved 90 degrees and about the same result.

This pole where the transformer is located is nect to the road.

Along the curb 12 ft from the pole inserted a probe (thus 12 ft from the pole ground rod), and continued along the curb another 12 ft and the voltage difference between the two probes was 0.011 V.

Next I went to the point where my water line connects to the street. Placed a probe 15 ft from the curb just above the water line. This water line is about 6 to 8 ft below ground surface. Place another probe 12 ft from the first going away from the street and above the water line. Voltage difference was 0.001 V. This is a north-south direction. The second probe was moved 12ft to the east and perpendicular to the water line. East voltage drop 0.016 to 0.017 V. Moved second proble to a point 12 ft west and the voltage was 0.006 V.

Middle of back yard 12 ft apart and north-south was 0.001 V, and east-west 0.002 V.

You can expect quite different results.

.

 

[meternerd]

One thing that gets people worried the most (at least when we, as utility guys, show up) is proximity to transmission lines and whether or not they are going to cause cancer. Well, fact is that most of the time, the magnetic fields of three phase high voltage AC transmission lines tend to cancel each other out, so the net induced voltage is negligible. A single phase tap of medium voltage can be a much greater source of EMF. Different story in a substation, though. Close proximity to high voltage bussing can give you a pretty good zap if you touch a ground while working around it. I know from personal experience. Ouch! Ditto on the high impedance meter and "phantom" voltage readings. Meaningless!

 

[ghostbuster]

A 5 foot dia. loop of wire (front lawn of house) beside a 230 kv. transmission generated 1 amp current flow in loop.Moving to backyard produced 2 amps of current flow.(This is from an engineering tech article that is too large to post here in this forum.)

 

[meternerd]

A 5 foot dia. loop of wire (front lawn of house) beside a 230 kv. transmission generated 1 amp current flow in loop.Moving to backyard produced 2 amps of current flow.(This is from an engineering tech article that is too large to post here in this forum.)

A 5 ft loop of wire could have very little resistance. If it was one mili-ohm, one amp would exist if there was one volt induced. Coil it up a bunch of times and you made a transformer, so you'd expect some current.

I used to take mili-gauss readings for paranoid customers and the readings from their electric blankets and toasters were huge compared to those near our 345 KV transmission line. Just my personal observations, though. Never did any in-depth studies.

 

[GoldDigger]

I used to take mili-gauss readings for paranoid customers and the readings from their electric blankets and toasters were huge compared to those near our 345 KV transmission line. Just my personal observations, though. Never did any in-depth studies.

A lot will depend on the orientation of the three phase wires (and maybe neutral) on the pole as well as how well the balance of the transmission line is maintained.

The farther apart the phase wires are the farther away you have to go to have the magnetic field decreased by any particular percentage as a result of cancellation.

I remember seeing somewhere a program that calculates the residual magnetic and electric field at any distance along the ground for a variety of wire geometry and height of transmission lines above the ground.
Probably linked in another post that I cannot find.

 

[gar]

140429-1318 EDT

aaronoraa:

Have you performed any new tests that can provide more information on your problem?

.