electric fences

Hmmm... then why am I afraid of accidently touching our Cooma neighbour's electric fence around their house again? Last time I did I was zapped big-time... rubber-soled workboots and all...........

I'm not a lecky , but , if a Lecky line falls on your vehicle , you dont automatically get electrocuted. It needs to be grounded.

an electric fence discharge will escape the rubber insulation of normal boots...thats where a lot of fly fishermen get caught out....one has to remember its only high volts and its the volts that JUMP.....been there done that..hahaha

Hmmmmmmmmmmmmm yes i do agree from personal experience....totally shocking...but the resuting erection put the Harbour bridge to shame.....

Geez, I hope my missus doesn't read this!!!
(she'll be rushin' out to buy an electric fence!!!)
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Then again..................... hmmmmm...
could be (ahem) "exciting"....

Hi ED C, My wife put an electrified fence down the middle of the bed.. I think it meant the opposite to your post. Anyway not so bad but i drew the the line when the Barbed wire went on the top of the fence.!!!!
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why ?

What the normal practice is to run the Positive from the controller to the live wire, the Neg is attached to a grounding post. This works well in moist ground as the current flows back to the controller when the live wire is touched.

Gravelly or dry ground is a bad conductor so as well as using a grounding post you attach the rest of the fence to the neg terminal.

All that is then need is to touch the live wire and the other fencing wire and zap you dont even need to touch the ground.

Is this what you mean with your question?

I agree with Alan S, being in the security industry myself I know first hand that it is common practice to eath to either the protection fence/poles or another section of the fence that is not live. In most security purposes you are trying to stop people jumping/clibming fences, where they are not always touching the ground. Plus the obvious earthing problems with shoes etc. Cattle might not wear shoes or jump but people certainly do! ;-)

And yes it is just a much more reliable way of doing things, you cannot gurantee that the person/animal is going to get a good earth just by standing on the ground out bush.

Yep , thanks for that.

Twas an honest question , didn't know the answer.

PS , the security fence cleared it up . . . hadn't thought of that.

And that would be revolting....sorry couldnt help it.....i would say that 99 times out of 100, you would be alright if you touched the fence, and once, when you were in a hurry to get things done b4 church, you would be stranded....to look at it from another direction....the volts wouldnt do the computer any good.....remember that the sparkplugs are earthed to the motor block aswell, so maybe the fence black box wont like that either....
Andrew

>Apart from Induced EMF, voltage spikes and static electricity,
>isnt this all about the path of least resistance. ie wouldnt the
>electric pulse (most elec fences are pulsed) travel from the
>live wire, into the panel of the vehicle (or bull bar, side step
>etc) and straight back into the negative of the erected fence.

Nope :)

That's why it's complex. Of course Ohms law applies to the DC components of the current as does Kirchoffs Law
http://physics.bu.edu/~duffy/PY106/Kirchoff.html
so some DC currents will flow through paths of more resistance.

However brushing an electric fence with a vehicle would also
produce a lot of AC currents and how they would behave would take a Cray Computer and a better engineer than me to analyse. Actually the DC component would be bloody complex too!

Like I said before - it might be OK, but I wouldn't do it :)

Mike Harding

Sorry Mike
i don't see were your coming from
Kirchoffs law applies to parallel circuits of resistance (ie resisters) not the entry and exit point of the electric current?
As Matt says if the vehicle touches the wire the shortest path will be taken to ground, if there is no path to ground then there can be no flow off electrons, as I can see it.
Both AC & DC need the flow of electron to create current the only difference is one crosses the line - to + and some impedance.
my only knowledge is that I left school
Regards

Richard Kovac

Hi Richard

>i don't see were your coming from

I sometimes wonder, myself! :)

>As Matt says if the vehicle touches the wire the shortest path
>will be taken to ground, if there is no path to ground then
>there can be no flow off electrons, as I can see it.

This is one of those things which would be easy to explain with a pencil and paper, anyway we'll give it a go....

Essentially (if one pole of the fence is connected to ground) there are four return paths for the current ie. 4 tyres. I'm assuming the tyres would not be perfect insulators at high voltage. From the point of contact with the fence _some_ current will flow to ground via _all_ four tyres - how much will return via _each_ tyre will be dependant upon the resistance (for the DC component) and the reactance (for the AC component). Measuring or calculating the impedance (resistance and reactance combined) through each of those paths would be next to impossible. Things get even more complicated because each of those four paths will have many sub paths through which current will flow and one of those sub paths _may_ be through the vehicle electronics? And that may cause damage.

Think of the vehicle as being thousands of resistors in parallel (Kirchoff) between the fence and earth - each resistor will carry some current but the lowest value resistor will carry the most and the highest value resistor the least.

Your are correct about current flow being the flow of electrons from atom to atom - well, actually, I think it's the "holes" which move - but I never understood all that stuff - personally I think it's all black magic :)

>Still Getting there

Aren't we all! :)

Mike Harding

mike_harding@fastmail.fm