Shielded cable for electric fence?

Lumen

I have a mains energiser for my electric poultry netting, with a ~30m lead out cable. The voltage is a few kV DC on a short pulse with 1 second interval.

The energiser is in my house and the lead out cable is the standard insulated 2.5mm solid core type from the local coop.

One of my neighbours (approx 100m away) has a recording studio, and since I switched from a battery energiser next to the fence to the mains+lead out has been getting interference manifested as a clicking noise when the gain is turned up. It's definitely my fence setup as when I turn it off the clicking disappears.

The first theory was that it was mains interference, but their sparks has suggested it might be radiated interference, presumably inducing a voltage.

I'm not really happy with the solid core, the outer is quite brittle and it got slightly damaged before I ran it under the ground, and as a result shorts out when the soil is waterlogged.

So I was wondering whether there might be a shielded cable I can use that would be suitable for high voltage, and would possibly stop it from radiating the pulse. It doesn't need to be armoured as there's no safety issue.

Ideas?

Stoner

Lumen wrote:

So I was wondering whether there might be a shielded cable I can use that would be suitable for high voltage, and would possibly stop it from radiating the pulse. It doesn't need to be armoured as there's no safety issue.

Hi.

Had a quick read, not sure why there is no safety issue, maybe look at that again


But anyway, you've possibly two components here with electrical and magnetic interference.


A long time ago I worked in R&D in this area, it's funny what can change this.

Anyway, the armoured core on an swa cable is a shield, it's not exactly continuous but it does an industry recognised job when installed correctly.

Secondly is there a switching mode power supply in your set up ? there are rings you can place over the cables to suppress this type of interference, note the amount, type and positioning of these is significant.

Installing cables in steel conduit or trunking can suppress interference too.

Lumen

Stoner wrote: »

Hi.

Had a quick read, not sure why there is no safety issue, maybe look at that again

But anyway, you've possibly two components here with electrical and magnetic interference.

A long time ago I worked in R&D in this area, it's funny what can change this.

Anyway, the armoured core on an swa cable is a shield, it's not exactly continuous but it does an industry recognised job when installed correctly.

Secondly is there a switching mode power supply in your set up ? there are rings you can place over the cables to suppress this type of interference, note the amount, type and positioning of these is significant.

Installing cables in steel conduit or trunking can suppress interference too.

No safety issue because you can hold on to the live terminal and only get a mild shock, the current is tiny despite massive voltage.

I guess as you point out, I don't know whether the interference is from the lead out cable or the energiser, although I'm guessing it's from the cable as my previous energiser (co-located with the fence) didn't cause this issue.

Why is solid core used in electric fence lead out cables? I don't really understand the physics. From what I (dimly) recall electricity is conducted over the surface of wires.

I was hoping to avoid SWA as it's so expensive. Would regular coax (of the sort used for TV aerials) do it? That has a solid core, right?

Lumen

This is what I have right now.

Lumen

I see I can get 3 core SWA315 (1.5 Sq mm) for €1.25 ex VAT per metre.

Is that 1.5sqmm per core? I guess I could connect the cores together for lower resistance.

Stoner

I don't know why it has to be solid core.

That cable would be 1.5 mm CSA per core.

You can double the cores if they are exactly the same size

whizbang

Coax will have the required insulation resistance. Fixed Installation types often have a very inflexible core, so not really suitable here.

Definitely worth trying, I'm sure you can pick up a length very cheap. Try it wired both ways before deciding.

Have you an earth connection on both sides of the energiser ?

Lumen

whizbang wrote: »

Have you an earth connection on both sides of the energiser ?

Not quite sure what you mean by "both sides". Sorry for ignorance!

The second energiser terminal is connected via crocodile clip to a copper pipe next to my washing machine. The electric netting itself is not earthed as such, it just has the connection from the lead out cable connected to a metal plate via another crocodile clip.

I think I read somewhere that earthing the energiser as I have via a copper pipe (rather than a ground spike) is a bad idea, but I'm not sure why.

whizbang

Best next thing for electrical noise, would be to use an earth spike right beside the connection to the netting, via coax.

Generally the earthed (if it is!) copper piping in your house will have a lower resistance path to the mains neutral, which is shared with your neighbour.

...probably why is a bad idea.

Nekarsulm

Lumen wrote: »

Not quite sure what you mean by "both sides". Sorry for ignorance!

The second energiser terminal is connected via crocodile clip to a copper pipe next to my washing machine. The electric netting itself is not earthed as such, it just has the connection from the lead out cable connected to a metal plate via another crocodile clip.

I think I read somewhere that earthing the energiser as I have via a copper pipe (rather than a ground spike) is a bad idea, but I'm not sure why.

Electric fences need very good earths. Clipping it to your plumbing is not good enough, and this is proven by your statement "you can hold the live, snd only get a mild shock"
It should lift you off the ground, and leave you thinking someone has walloped you with a 4 by 2.
You need three earth rods driven full lenght into the (damp)ground, each 5 meters further away, and connected to your fencers earth pole with a single unbroken lenght of high tensile wire, itself clamped to the earth rod with proper U clamps.
Have a look in the farming forum here on Boards, loads of stuff about fencing systems.
(In very dry weather, farmers water their earth rods!)

2011

Nekarsulm wrote: »

Electric fences need very good earths.

+1

Clipping it to your plumbing is not good enough

.....or advisable as you are now encouraging a current to flow through your pipework.

You need three earth rods driven full lenght into the (damp)ground, each 5 meters further away, and connected to your fencers earth pole with a single unbroken lenght of high tensile wire, itself clamped to the earth rod with proper U clamps.

This would make sense to me.

2011

Lumen wrote: »

One of my neighbours (approx 100m away) has a recording studio, and since I switched from a battery energiser next to the fence to the mains+lead out has been getting interference manifested as a clicking noise when the gain is turned up. It's definitely my fence setup as when I turn it off the clicking disappears.

I am often have mitigate the risks of EMI (electromagnetic interference) issues that are caused by high frequency switching. Obviously you are not switching at high frequency but the symptoms sound similar. I am not an expert in this but here is what I think:

There are 2 types of EMI that you need to consider:

1) Radiated, this is dealt with by robust screening, equipotential bonding and earthing. Think of a Farady cage. This causes interference with other items that are "within range" of the magnetic field that it is radiating. I would think that your neighbour is too far away for this to be the issue.

2) Conducted, this is interference that is causes issues with other equipment because it is electrically connected to it. I would suspect that this is the issue that you have. This issue can be dealt with by installing active filters (expensive) or passive filters (cheap).

I'm not really happy with the solid core, the outer is quite brittle and it got slightly damaged before I ran it under the ground, and as a result shorts out when the soil is waterlogged.

I don't think the shorting is due to the cable being solid core. It is more likely:
1) The insulation is damaged / poor cable joint that gets waterlogged.
2) The insulation is not rated for a voltage that high.

I doubt that the cable you are using is designed to be direct buried, and SWA is.

So I was wondering whether there might be a shielded cable I can use that would be suitable for high voltage, and would possibly stop it from radiating the pulse. It doesn't need to be armoured as there's no safety issue.

As Stoner suggested SWA would be better. This is unlikely to be rated for your voltage but will most likely work. Even if i does not solve your problem entirely it is far more robust and is UV resistant which your cable may not be.

From what I (dimly) recall electricity is conducted over the surface of wires.

At higher voltages, it is know as the "skin effect".

Nekarsulm

And don't use copper cored wire to join either the fencer output to the actual fence, nor as an earth wire. Especially don't use copper wire to join to high tensile galvanised wire.

my3cents

Stoner wrote: »

Hi.

...

Secondly is there a switching mode power supply in your set up ? there are rings you can place over the cables to suppress this type of interference, note the amount, type and positioning of these is significant.

...

Tried the ferrite rings for a very similar issue and found they were a total waste of time.

The problem we have is that Radio 4 long wave (LW always susceptible to interference anyway) picks up the nearest electric fence. Interesting feature is that its worse (louder on the radio) when the grass is long and the weather is wet.

It may be Lumen has just created an antenna of just the right length for creating interference. So just playing with the length of the cable might be of some benefit. But found quality earthing as already suggested improved but not fixed the problem, which was also related to crappy power from Networks Ireland them putting in a new transformer also made a difference.

May I suggest using a portable LW radio tuned to the worst tick of the interference to help troubleshoot?

TheChizler

2011 wrote: »

At higher voltages, it is know as the "skin effect".

Higher frequencies, rather than voltage, right? Others HV distribution lines wouldn't work.

I'm surprised that this is happening if the neighbour has a professional recording studio, power and ground loop interference suppression systems should be fitted as standard right?

Say my name

A trick some farmers used to find an earth or short or break in the electric fence itself was to use a battery radio and walk along the fence wire till it picked up the break or earth in the fence.

As Nekarsulm posted a proper earth system is key on the fencer unit.
I use that covered cable to connect to my earth bars and just striped where it connects to the earth bars. It has to be continuous cable with no joints and U bolted to the earth bars and you'll never have enough of earth bars. The more the merrier.

I your really worried about that lead cable from the fencer to the fence, you could run it into a half inch hydrodare pipe up to the fence.

2011

TheChizler wrote: »

Higher frequencies, rather than voltage, right?

Yes, my bad.

Nekarsulm

Say my name wrote: »

It has to be continuous cable with no joints and U bolted to the earth bars and you'll never have enough of earth bars. The more the merrier.

I heard of a farmer who brazed the earth wire to a scrapped Hillman Hunter car that was lying around the farm, and then buried it...

But a few good earth rods would probably be good enough...

2011

Nekarsulm wrote: »

I heard of a farmer who brazed the earth wire to a scrapped Hillman Hunter car that was lying around the farm, and then buried it...

:D

But a few good earth rods would probably be good enough...

Funnily enough I was witnessing the testing of an earth pit several years ago. From memory we had to get the resistance to < 5Ω between the earth pit and the general mass of earth. We would test, measure the resistance, add additional earth rods and repeat until the resistance was sufficiently low. What I wound interesting was that the horizontal conductors that we used (50 x 3mm bare copper) did more to improve the earth pit than the electrodes. This is worth noting when trying to make a solid connection to earth for the electric fence.

Say my name

Nekarsulm wrote: »

I heard of a farmer who brazed the earth wire to a scrapped Hillman Hunter car that was lying around the farm, and then buried it...

But a few good earth rods would probably be good enough...

Some chancers about alright!

There's also the option of using diatomaceous earth around those rods too.

The op has to be having the shock from the fencer travelling along that copper pipe, with what they're after describing.
I had a problem myself one time with vegetation on the fence and the shock going into the earths and anytime you touched both water taps in the bathroom there was a shock from the fencer. The fencer was in a garage beside the house and the earth bars along side near the house.

Reisers

Esbn use bare copper for earthing

2011

Reisers wrote: »

Esbn use bare copper for earthing

They are not alone

Nekarsulm

Reisers wrote: »

Esbn use bare copper for earthing

Not denying that, but in an electric fence energiser setup, where the fence wire is usually galvanised , copper is a bad choice to use as a lead between the fencer and the galvanised wire.
It always corrodes where the two are joined, and creates resistance.

2011

Nekarsulm wrote: »

It always corrodes where the two are joined, and creates resistance.

+1

This reaction between dissimilar metals is particularly pronounced in marine environments.

TheChizler

2011 wrote: »

+1

This reaction between dissimilar metals is particularly pronounced in marine environments.

What would be best here? Some sort of brass connector in between?

2011

TheChizler wrote: »

What would be best here? Some sort of brass connector in between?

To deal with corrosion in general sacrificial anodes are commonly used in marine environments.

For electrical connections it is best to avoid different metals being in contact with each other. If connecting say copper to aluminium special lugs like this can be used: