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Electric fence installation / doesn't work
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<blockquote data-quote="dcara" data-source="post: 98284" data-attributes="member: 473"><p>1st a word on safety. If for some reason you have to touch a wire you think might be live, do it with the back of your hand or back of your finger. As Bama said, the electrical charge will make muscles contract. So if you touch with the back side your hand or finger naturally pulls away. If you touch with the inside then your hand or finger will grab the wire when the muscle contraction happens and you may not be able to let go.</p><p></p><p>As far as the physics of it go, it is often said that it is the electrical current that will hurt you. But there has to be enough voltage to push the current through what ever resistance exists. The simple equation that defines this relationship is called Ohms Law and is stated as voltage(v) divided by resistance(r) = current(I). Written I=V/R. So the higher the voltage for a given resistance the higher the current, and the higher the resistance for a given voltage the lower the current. Everyone has seen the Van degraph generators in science class that make your hair stand on end when you touch them, or even a comb with static electricity that attracts your hair from 2 inches away. In these examples there are 10's of thousands of volts at play but the resistance is so high that there is little current to speak of. So then it is really the combination/product of voltage(v) and current(I) refered to as power that will get you. Where power(p) in watts = V*I.</p><p></p><p>Human skin resistance itself can vary from a few hundred ohms to about 50 thousand ohms (called 50k ohms) depending on moisture content. Generally women call feel slightly lower voltage shocks than men because they typically have more moist skin which has the added benifit of making them nice and soft.javascript:emoticon('<img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" />')</p><p>Smile</p><p></p><p>Dun - assuming your skin resistance and overall contact resistance (i.e total path resistance) to ground were the same for the 500V and 800V tests then by ohms law the 800 volts would push 60% more current through you vs. the 500V. Hence your body (actually total path) would have to absorb 60% more more power so I think you could feel the differene between 1mA and 1.6mA. Your example though compared the same currents at different voltages (i.e. 500V*1mA=0.5 W vs. 800V at 1mA) which implies a 60% increase in path resistance. None-the-less the total power of 800V@1mA is 60% more than 500V@1mA so I think you would also feel that. Fence chargers are actually rated in terms of power by specifying their voltgage and current (i.e. V*I=P). Some are rated in Joules which is just watts per second. That is 120V*0.1A = 12W = 12J/s = 12000V@1mA.</p><p></p><p>Someone asked about grass and weeds touching the wire. Yes they will reduce the charge on your fence if they touch it. I've also seen fences that don't work in the morning if there is enough dew on the insulator to give the charge a path to ground through the post it is connected to.</p><p></p><p>Sorry about the rambling, I just got going. <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite1" alt=":)" title="Smile :)" loading="lazy" data-shortname=":)" /></p></blockquote><p></p>
[QUOTE="dcara, post: 98284, member: 473"] 1st a word on safety. If for some reason you have to touch a wire you think might be live, do it with the back of your hand or back of your finger. As Bama said, the electrical charge will make muscles contract. So if you touch with the back side your hand or finger naturally pulls away. If you touch with the inside then your hand or finger will grab the wire when the muscle contraction happens and you may not be able to let go. As far as the physics of it go, it is often said that it is the electrical current that will hurt you. But there has to be enough voltage to push the current through what ever resistance exists. The simple equation that defines this relationship is called Ohms Law and is stated as voltage(v) divided by resistance(r) = current(I). Written I=V/R. So the higher the voltage for a given resistance the higher the current, and the higher the resistance for a given voltage the lower the current. Everyone has seen the Van degraph generators in science class that make your hair stand on end when you touch them, or even a comb with static electricity that attracts your hair from 2 inches away. In these examples there are 10's of thousands of volts at play but the resistance is so high that there is little current to speak of. So then it is really the combination/product of voltage(v) and current(I) refered to as power that will get you. Where power(p) in watts = V*I. Human skin resistance itself can vary from a few hundred ohms to about 50 thousand ohms (called 50k ohms) depending on moisture content. Generally women call feel slightly lower voltage shocks than men because they typically have more moist skin which has the added benifit of making them nice and soft.javascript:emoticon(':)') Smile Dun - assuming your skin resistance and overall contact resistance (i.e total path resistance) to ground were the same for the 500V and 800V tests then by ohms law the 800 volts would push 60% more current through you vs. the 500V. Hence your body (actually total path) would have to absorb 60% more more power so I think you could feel the differene between 1mA and 1.6mA. Your example though compared the same currents at different voltages (i.e. 500V*1mA=0.5 W vs. 800V at 1mA) which implies a 60% increase in path resistance. None-the-less the total power of 800V@1mA is 60% more than 500V@1mA so I think you would also feel that. Fence chargers are actually rated in terms of power by specifying their voltgage and current (i.e. V*I=P). Some are rated in Joules which is just watts per second. That is 120V*0.1A = 12W = 12J/s = 12000V@1mA. Someone asked about grass and weeds touching the wire. Yes they will reduce the charge on your fence if they touch it. I've also seen fences that don't work in the morning if there is enough dew on the insulator to give the charge a path to ground through the post it is connected to. Sorry about the rambling, I just got going. :) [/QUOTE]
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