Electric fencing, circuits and leakages.

L1985 · 10-06-2019 11:58pm #1

Really stupid question for ye....I presume if a fence tester is showing 4 in one area it’s 4in every area....my dads trying to get me to test each section separately today but I was arguing that they are the same only to realize I’m not 100% they are.....all on the same circuit. I was crap at science in school ðŸ™ˆ

carrollsno1 · 11-06-2019 4:59am

L1985 wrote: »

Really stupid question for ye....I presume if a fence tester is showing 4 in one area it’s 4in every area....my dads trying to get me to test each section separately today but I was arguing that they are the same only to realize I’m not 100% they are.....all on the same circuit. I was crap at science in school ðŸ™ˆ

Id imagine theyd be the same in each paddock but not all around the farm.
Ive a question about electric fences now that you reminded me.
Is the current stronger in a line compared to a loop? A farmer before told me it was stronger in a line compared to a loop but he was the only one ever mentioned it or had it done in 4 countries ive farmed in!
No fences where i am at the minute at all just a gap of a few yards between the crops is all now.

blue5000 · 11-06-2019 9:01am

I think the further you go from the earth the weaker it gets, especially if ground is dry. I find in wet weather power is lost through strainers with the bryce pads.

emaherx · 11-06-2019 9:36am

L1985 wrote: »

Really stupid question for ye....I presume if a fence tester is showing 4 in one area it’s 4in every area....my dads trying to get me to test each section separately today but I was arguing that they are the same only to realize I’m not 100% they are.....all on the same circuit. I was crap at science in school ðŸ™ˆ

No, your dad's probably correct. If you have a straight line out from fence unit and test the furthest end, you can assume the rest is the same or better, but if the line has branches off of it then each branch can develop its own fault so you should test the furthest end of each of these too.

emaherx · 11-06-2019 9:42am

carrollsno1 wrote: »

Is the current stronger in a line compared to a loop? A farmer before told me it was stronger in a line compared to a loop but he was the only one ever mentioned it or had it done in 4 countries ive farmed in!
No fences where i am at the minute at all just a gap of a few yards between the crops is all now.

There will be very little difference if any between a loop and a straight line in ideal conditions. Your electric fence "should" be an open circuit until an animal comes in contact and completes the path to ground. A loop is more fault tolerant so if there is a break or a single bad earth there will be an alternate route keeping most of the fence live in both directions.

Buford T. Justice XIX · 11-06-2019 9:57am

L1985 wrote: »

Really stupid question for ye....I presume if a fence tester is showing 4 in one area it’s 4in every area....my dads trying to get me to test each section separately today but I was arguing that they are the same only to realize I’m not 100% they are.....all on the same circuit. I was crap at science in school &#55357;&#56904;

No, as blue said above the tester will only show the current at that particular point.

If you have a branch off to a different section and that section has a bad earth, if you disconnect to supply to that section then the current to the other sections will increase as the current has no easy way to reach the earth.

Fixing the earthing bit of the wire and turning the fence on again to that section will get a small drop in the overall current at the first point tested but a huge jump where the earthed section is fixed, if that makes sense?

L1985 · 11-06-2019 10:18am

Ok ok still confused....just because it’s all on one circuit with branches off but loops back I would have thought the electricity couldn’t vary from one part of the line to another if they are connected?
I googled this as well and
“Search Results
Featured snippet from the web
When a voltage source is connected to a circuit, the voltage will cause a uniform flow of charge carriers through that circuit called a current. In a single (one loop) circuit, the amount of current at any point is the same as the amount of current at any other point”
Again ppl here are prob right but I’m just trying to wrap my head around it....

emaherx · 11-06-2019 10:54am

L1985 wrote: »

Ok ok still confused....just because it’s all on one circuit with branches off but loops back I would have thought the electricity couldn’t vary from one part of the line to another if they are connected?
I googled this as well and
“Search Results
Featured snippet from the web
When a voltage source is connected to a circuit, the voltage will cause a uniform flow of charge carriers through that circuit called a current. In a single (one loop) circuit, the amount of current at any point is the same as the amount of current at any other point”
Again ppl here are prob right but I’m just trying to wrap my head around it....

The "loop" as in circuit is not any loop you may or may not create in the fence system, the "loop" in a circuit sense the current flows out of the live terminal out to the fence but back through the earth. You need to consider the animal touching the fence and the ground all the way back to your earth rod as part of the circuit.

The reason one line may vary is because it may have earthing caused by vegetation, fallen wire or contact with something metallic, which allows current to flow back to earth, potentially making anything further down the line useless. Electricity will always flow through the path of least resistance, everything after that will have reduced power potentially down to near 0v.

emaherx · 11-06-2019 11:08am

See picture, the current flows as far as the cow then back to fence unit. (There will be some current down the line as a cow is not a perfect conductor but it will be reduced temporarily till she moves. If you replaced cow with an iron bar everything after the bar will be essentially dead and no longer forms part of circuit. Also enough earthing from vegetation can kill the rest of the fence)

Also in the iron bar example or any bad enough earth the power between fence and earthing will be some what reduced getting worse the closer you get to the bar as you or your cattle are not as good a conductor as the iron bar.

_Brian · 11-06-2019 11:23am

There is also the issue of resistance at joints, leakage at insulators and the difference in wire types.
We have heavy steel wire at the permimiter but inside it’s a mix of steel tie wire and white. With the combination of earths, connections and potentially leaking insulators it’s massively complicated.

Power does strange things in lines that you wouldn’t expect.
Ever notice during a lightening storm lights dim occasionally ? That’s a strike on the grid, you’d expect a surge rather than a dim. But locally to the strike the burst of power temporarily lowered resistance in that section causing local power to flow towards the lowered resistance and the result can be a dip in power at other local locations.

I would never test one section of fence and presume the others are fine.

Obviously the use of copper wire to join sections is a big no no. Where the copper and steel wires join they are dissimilar metals on the presence of voltage and damp and so create an oxide film between them which over time insulated them from each other, causing a gradual drop in power transferred until eventually no power is transferred.

emaherx · 11-06-2019 11:29am

_Brian wrote: »

There is also the issue of resistance at joints, leakage at insulators and the difference in wire types.
We have heavy steel wire at the permimiter but inside it’s a mix of steel tie wire and white. With the combination of earths, connections and potentially leaking insulators it’s massively complicated.

Power does strange things in lines that you wouldn’t expect.
Ever notice during a lightening storm lights dim occasionally ? That’s a strike on the grid, you’d expect a surge rather than a dim. But locally to the strike the burst of power temporarily lowered resistance in that section causing local power to flow towards the lowered resistance and the result can be a dip in power at other local locations.

I would never test one section of fence and presume the others are fine.

Obviously the use of copper wire to join sections is a big no no. Where the copper and steel wires join they are dissimilar metals on the presence of voltage and damp and so create an oxide film between them which over time insulated them from each other, causing a gradual drop in power transferred until eventually no power is transferred.

That's all very true. This topic could nearly be a thread of it's own.

_Brian · 11-06-2019 11:39am

emaherx wrote: »

That's all very true. This topic could nearly be a thread of it's own.

Early 90’s I did a training course with Alfa, would be good for all farmers.

L1985 · 11-06-2019 11:55am

Thanks guys that makes a lot More sense to me!! As I said I’m crap at science so thanks for all the explanations that now gives me some logic behind it. And damn it dad was right!!!
So testing the end of lines would be good practice as well! Having major issues with the fence at the moment so spending a lot of time fixing problems.

emaherx · 11-06-2019 12:01pm

L1985 wrote: »

And damn it dad was right!!!

I've found myself saying that a lot more often than I thought I would since taking over the farm.

ganmo · 11-06-2019 12:05pm

don't tell him though it'll go to his head :P

emaherx · 11-06-2019 12:13pm

_Brian wrote: »

Power does strange things in lines that you wouldn’t expect.
Ever notice during a lightening storm lights dim occasionally ? That’s a strike on the grid, you’d expect a surge rather than a dim. But locally to the strike the burst of power temporarily lowered resistance in that section causing local power to flow towards the lowered resistance and the result can be a dip in power at other local locations.

I work as an engineer in the industrial print industry. Machines use static electricity and lasers to put toner on paper passing through them at over 300m/min.

Electricity doing strage things and taking unexpected paths is not an uncommon problem for me.

_Brian · 11-06-2019 12:18pm

emaherx wrote: »

I work as an engineer in the industrial print industry. Machines use static electricity and lasers to put toner on paper passing through them at over 300m/min.

Electricity doing strage things and taking unexpected paths is not an uncommon problem for me.

Yea, I miss industrial work if I’m honest. I worked in the semiconductor industry for a long time and the high end technology is very interesting to work on.

L1985 · 11-06-2019 12:22pm

ganmo wrote: »

don't tell him though it'll go to his head :P

Oh that won’t be happening!! I’ll never hear the end of it. And there is enough on his “never hear the end of it” list as it is!

emaherx · 11-06-2019 12:23pm

_Brian wrote: »

Yea, I miss industrial work if I’m honest. I worked in the semiconductor industry for a long time and the high end technology is very interesting to work on.

Big stuff is great, because it works just the same as the smaller stuff, but you can see it, and the individual processes are separated out so it's easier to understand. (But more likely to kill you if you don't

)

visatorro · 11-06-2019 12:43pm

_Brian wrote: »

Yea, I miss industrial work if I’m honest. I worked in the semiconductor industry for a long time and the high end technology is very interesting to work on.

Once your happy that's all that matters. I don't like my job but it pays the bills. Well a few bills anyway, not exactly living like a king ðŸ‘‘

_Brian · 11-06-2019 12:48pm

visatorro wrote: »

Once your happy that's all that matters. I don't like my job but it pays the bills. Well a few bills anyway, not exactly living like a king &#55357;&#56401;

Wise words.
Work to live not live to work.

My current role is grand, I have a great immediate manager and it’s hugely flexible which works well with family life.

Nekarsulm · 11-06-2019 1:26pm

emaherx wrote: »

I work as an engineer in the industrial print industry. Machines use static electricity and lasers to put toner on paper passing through them at over 300m/min.

Electricity doing strage things and taking unexpected paths is not an uncommon problem for me.

Is it not the case that electricity actually flows from negative to positive, though?

emaherx · 11-06-2019 1:27pm

L1985 wrote: »

Thanks guys that makes a lot More sense to me!! As I said I’m crap at science so thanks for all the explanations that now gives me some logic behind it. And damn it dad was right!!!
So testing the end of lines would be good practice as well! Having major issues with the fence at the moment so spending a lot of time fixing problems.

Yea, test the end of the lines, if you find a fault work back to where you have good voltage and you will find the issue.

If you are having issues everywhere make sure you have good earthing at fence unit. Depending on area covered you may want multiple earth rods, especially on dry land.

ganmo · 11-06-2019 1:30pm

Nekarsulm wrote: »

Is it not the case that electricity actually flows from negative to positive, though?

Yup electrons are negatively charged

_Brian · 11-06-2019 1:31pm

emaherx wrote: »

Yea, test the end of the lines, if you find a fault work back to where you have good voltage and you will find the issue.

If you are having issues everywhere make sure you have good earthing at fence unit. Depending on area covered you may want multiple earth rods, especially on dry land.

For a mains fencer it’s recommended to have 3 1meter earth rods min 1 meter apart.

If your worried about the earthing you should be able to touch the earth rod and not get a shock, if you get a shock it means your earthing is insufficient. This may be too small of earth system or poor ground under the earths.

Problem is earths are often tucked under hedges or along walls where the ground is terribly dry and so less conductive. In dry weather I’d have to turn a hose along ours and let it soak for a few hours to wet the ground.

Never ever use the steelwork of a shed to earth a fencer. It will affect the cattle and often because of the concrete and stone round them they actually earth quite poorly.

Buford T. Justice XIX · 11-06-2019 1:36pm

emaherx wrote: »

Yea, test the end of the lines, if you find a fault work back to where you have good voltage and you will find the issue.

If you are having issues everywhere make sure you have good earthing at fence unit. Depending on area covered you may want multiple earth rods, especially on dry land.

^^^
This x 1000!

I've gotten in the habit of filling a few buckets of wash at the end of milking and carrying them as far as the earth rods after milking every evening and throwing them onto the earth around the rods.

wrangler · 11-06-2019 1:44pm

_Brian wrote: »

For a mains fencer it’s recommended to have 3 1meter earth rods min 1 meter apart.

If your worried about the earthing you should be able to touch the earth rod and not get a shock, if you get a shock it means your earthing is insufficient. This may be too small of earth system or poor ground under the earths.

Problem is earths are often tucked under hedges or along walls where the ground is terribly dry and so less conductive. In dry weather I’d have to turn a hose along ours and let it soak for a few hours to wet the ground.

Never ever use the steelwork of a shed to earth a fencer. It will affect the cattle and often because of the concrete and stone round them they actually earth quite poorly.

A lot of farmers don't appreciate how easy it is to lose voltage, I see some using sinlge core electric wire, wire that'd be barely able to carry 240 volts and they wonder why it won't carry 5000 volts.
Loose connections and poor insulators too will break you heart.
I bought a 6 joule Pel a few weeks ago, it's a lot more forgiving of poor fencing than what I had before

visatorro · 11-06-2019 2:06pm

Nekarsulm wrote: »

Is it not the case that electricity actually flows from negative to positive, though?

I thought it was positive to negative

Nekarsulm · 11-06-2019 2:10pm

visatorro wrote: »

I thought it was positive to negative

As far as I know, when electricity was being discovered this is what people thought.
So ever since, this has been how its been labelled.
You can see the way they were thinking, after all, lightning arc's to the earth.

emaherx · 11-06-2019 2:25pm

Nekarsulm wrote: »

Is it not the case that electricity actually flows from negative to positive, though?

Would it hurt any more/less?

emaherx · 11-06-2019 2:34pm

Nekarsulm wrote: »

As far as I know, when electricity was being discovered this is what people thought.
So ever since, this has been how its been labelled.
You can see the way they were thinking, after all, lightning arc's to the earth.

I think from a physics point of view you are absolutely correct, however nearly all circuit diagrams and in particular diagrams of components such as diodes suggest it flows the other way.

Electric fencing, circuits and leakages.

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