Electric Fencer Mystery, can it be solved?

[cmcgalla]

Hi all, so I had a professional install my fence for our cattle, goats, llama and pigs, just a pasture fenced in a rectangle with a bull pen integrated. The bull pen shares 2 sides with the main pasture fence. The posts are wood, the fence is woven wire and I have 2 hot wires, one at the top and one about 10" off the ground. The hot wires are totally isolated from the woven wire with insulators, as far as I can tell no hot wire touches the woven wire. They put 2 ground rods at separate locations and attached the woven wire to those rods. He said it was to prevent the electricity from arcing to the woven wire from to hot wire. I was thinking, "gosh if there is enough power to arc 8" that will kill my cattle", but he said that is how he does it.

See those 2 6' gates in the image, well when you touch both gates you get a little shock, as long as the gates are not touching.
If you are touching both gates and getting shocked and then close the gates so they touch you stop getting shocked.
The hardware that holds the gates was touching the woven wire on both gates, so I cut the woven wire so it would not touch the gate hardware and no more shock. Any idea what is going on?

Some thoughts:
Maybe some electricity is flowing underground from the 2 ground rods in the barn for the fencer (100' feet away) and in turn to the ground rods he installed for for the woven wire, thus energizing the woven wire and in turn the gate hardware, except for that one section that is not attached to a ground rod, effectively creating a potential difference from one gate to the other, thus the shock. I surmise that when you touch the gates together your making then equipotential and no shock. Possible?

The bottom hot wire does touch some grass, the grass touch the woven wire . . . can that be how the woven is getting energized?

Maybe the hot wire is touching the woven somewhere and I can't find it?

For now I have stopped the shocking part, but I want to know why this was happening and as far as I am concerned it is not fixed because the same electrical condition still exists, all I did was cut the woven wire as a temporary fix. The fence guy said it was mystery, I think not and I want to solve it.

e.

 

[kwired]

Is the woven wire on both sides of the gate electrically bonded together someplace or is one side isolated someplace?

If you have one of them isolated someplace you effectively made a capacitor out of things and you have an open terminal on a charged capacitor when you open the gate. The shock you are feeling is the discharge of that capacitor.

It is a rather crude capacitor, but remember the voltage is rather high, so it doesn't really have to be all that great of a capacitor. Apply less than 600 volts and you probably would feel nothing.

 

[cmcgalla]

fence

fence

NO the woven wire is not bonded on both sides of the gate. That fence that comes from the tire is a loaner, it is not connected to any ground rod,or any other fence parts.

BUT how is electricity getting to the woven wire? Through the earth?

I assume then that I should pound a rod and connect the loaner fence to it to create a bonded system that is equipotential?

Is the woven wire on both sides of the gate electrically bonded together someplace or is one side isolated someplace?

If you have one of them isolated someplace you effectively made a capacitor out of things and you have an open terminal on a charged capacitor when you open the gate. The shock you are feeling is the discharge of that capacitor.

It is a rather crude capacitor, but remember the voltage is rather high, so it doesn't really have to be all that great of a capacitor. Apply less than 600 volts and you probably would feel nothing.

 

[kwired]

NO the woven wire is not bonded on both sides of the gate. That fence that comes from the tire is a loaner, it is not connected to any ground rod,or any other fence parts.

BUT how is electricity getting to the woven wire? Through the earth?

I assume then that I should pound a rod and connect the loaner fence to it to create a bonded system that is equipotential?

Woven wire is charged from capacitive coupling.

Remember, a capacitor is two conductors separated by an insulator. You have two conductors with a pretty consistent spacing between them as the insulator. This is not a very useful capacitor for low voltages but these fence chargers are pretty high voltages, and this capacitor can store a fairly significant charge at those kinds of voltages. It is a high voltage but has very low current capabilities, that is why it doesn't kill the livestock. It can kill smaller animals. I have used electric fence to keep rabbits, raccoons, etc out of the garden, in order to keep a rabbit away it needs to be fairly low to the ground, I have found when that close to the ground it kills a lot of birds when they come in contact with it.

Earthing it will put it at same potential as earth. Closing the gate also puts it at same potential as the other portion that is earthed, which is why you are not shocked when the gates are touching each other.

 

[G._S._Ohm]

. . .it was mystery. . .

A shock is qualitative but numbers are quantitative so when in doubt, make measurements.

If you have a scope, make or buy a resistor that can withstand the max fence voltage pulse and use it to simulate your body. Try 3K at first and see what waveform you get.
Garden variety resistors can stand maybe 500v so you'd need several in series, both for the resistor and to make a voltage divider to protect your scope's input. Resistive spark plug wires may also work.

This method is also useful for tracing down stray voltages. You're looking to measure the source impedance.

 

[cmcgalla]

Now What?

Now What?

I need to look in to capacitive coupling to learn what it is . . . but I guess to be safe I should connect that loaner woven wire to a ground rod, in that case I will not get shocked even if holding both gates.

Is this whole situation an application of bonding, I understand bonding as connecting all metal parts together so as to ensure they are equipotential.
Thanks

 

[cmcgalla]

But how?

But how?

I must be missing something simple. You say the woven wire fence is charged from capacitive coupling, but where is the source of the electricity?
Do you think my hot wire is touching the woven wire?
Is electricity flowing through the earth?

Woven wire is charged from capacitive coupling.

Remember, a capacitor is two conductors separated by an insulator. You have two conductors with a pretty consistent spacing between them as the insulator. This is not a very useful capacitor for low voltages but these fence chargers are pretty high voltages, and this capacitor can store a fairly significant charge at those kinds of voltages. It is a high voltage but has very low current capabilities, that is why it doesn't kill the livestock. It can kill smaller animals. I have used electric fence to keep rabbits, raccoons, etc out of the garden, in order to keep a rabbit away it needs to be fairly low to the ground, I have found when that close to the ground it kills a lot of birds when they come in contact with it.

Earthing it will put it at same potential as earth. Closing the gate also puts it at same potential as the other portion that is earthed, which is why you are not shocked when the gates are touching each other.

 

[kwired]

I need to look in to capacitive coupling to learn what it is . . . but I guess to be safe I should connect that loaner woven wire to a ground rod, in that case I will not get shocked even if holding both gates.

Is this whole situation an application of bonding, I understand bonding as connecting all metal parts together so as to ensure they are equipotential.
Thanks

You understand how a transformer "induces" voltage from the primary coil to a secondary coil that has no direct electrical connection?

Capacitive coupling is the same thing but the "secondary voltage" is produced via capacitive properties instead of inductive properties, is about the simplest way I can describe it. It happens all the time in less than 600 volt applications, but quite often is unnoticed because the stored energy is not enough to do much of anything or even be felt if you come into contact with it, but with the electric fence and voltages that are likely 10,000 or more volts, you are more likely to feel it, but you generally do not suffer any injury or death because it is still a low level of energy that flows.

 

[cmcgalla]

OK

OK

Makes sense, so the close proximity of the hot wires to the woven wire is what is "charging" the woven wire, only to be discharged when the field collapses via me touching the gates . . right?

If the hot wires were farther from the woven wire I could reduce, or eliminate, the capacitive coupling, correct?

You understand how a transformer "induces" voltage from the primary coil to a secondary coil that has no direct electrical connection?

Capacitive coupling is the same thing but the "secondary voltage" is produced via capacitive properties instead of inductive properties, is about the simplest way I can describe it. It happens all the time in less than 600 volt applications, but quite often is unnoticed because the stored energy is not enough to do much of anything or even be felt if you come into contact with it, but with the electric fence and voltages that are likely 10,000 or more volts, you are more likely to feel it, but you generally do not suffer any injury or death because it is still a low level of energy that flows.

 

[kwired]

Makes sense, so the close proximity of the hot wires to the woven wire is what is "charging" the woven wire, only to be discharged when the field collapses via me touching the gates . . right?

If the hot wires were farther from the woven wire I could reduce, or eliminate, the capacitive coupling, correct?

That's right. Grounding the isolated section also drains the voltage away like we mentioned earlier, it would no longer be isolated.

Bonding the isolated section of woven fence to the main section of woven fence should also work to solve your problem.

 

[suemarkp]

I don't think you need a ground rod for that isolated fence section, just connect a wire to it so it is bonded to the other grounded fence sections. A ground rod would probably work too (although its impedance is higher than a wire), but seems like more work than just a jumper wire or two.

Also may want to ground the water tire -- not sure if it is totally insulated from the earth and picking up voltage in the water, but if it does you'd want to drain that voltage out to the earth (and ideally where they stand to drink out of the water).

 

[cmcgalla]

tire

tire

The water tire is a giant truck truck tire form a mining truck, its all rubber and the bottoem is sealed with concrete, so probably ok. But how would I ground that? Run a ground rod and then a wire into the water?

I don't think you need a ground rod for that isolated fence section, just connect a wire to it so it is bonded to the other grounded fence sections. A ground rod would probably work too (although its impedance is higher than a wire), but seems like more work than just a jumper wire or two.

Also may want to ground the water tire -- not sure if it is totally insulated from the earth and picking up voltage in the water, but if it does you'd want to drain that voltage out to the earth (and ideally where they stand to drink out of the water).

 

[kwired]

The water tire is a giant truck truck tire form a mining truck, its all rubber and the bottoem is sealed with concrete, so probably ok. But how would I ground that? Run a ground rod and then a wire into the water?

If bottom is concrete and sitting on the ground, it is probably grounded well enough, just earth the fence somewhere nearby, so there will be no potential between them. If the woven wire happens to pass over this just letting a wire dangle into the water would work pretty good also.

 

[CCC]

Electric Fence

Electric Fence

There should beonly one ground rode. The ground rode should be back at the source. That is thereason for isolate it form the post. As soon as you put the ground rods in theground the voltage is just going back to the source in whatever path in cantake all day long. The hot wire should be isolated all by its self and whensomething comes in contact with the wire that is what completes the circuit andshocks the animal or whatever touches the wire.

 

[kwired]

There should beonly one ground rode. The ground rode should be back at the source. That is thereason for isolate it form the post. As soon as you put the ground rods in theground the voltage is just going back to the source in whatever path in cantake all day long. The hot wire should be isolated all by its self and whensomething comes in contact with the wire that is what completes the circuit andshocks the animal or whatever touches the wire.

That is true for the "hot" wire. OP is having trouble with undesired voltage on wires not intended to be "hot". Grounding isolated items is one way to keep them at earth potential.