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Post by GTCGreg on Nov 21, 2014 16:19:28 GMT
A couple of points.
First, the second anode voltage of an old B&W TV was around 15,000 Volts. This will give you a nasty jolt even if you aren't grounded. While that's a pretty high voltage, it is limited to relativity low current. Enough to knock you on your butt, but probably not enough to kill you instantly.
Second. Yes, concrete is conductive but conductivity is relative. It's not a very good conductor. It has a low enough resistance to give you a good shock if standing on it in your bare feet and you touch a live 120 or 240 volt wire, but not conductive enough to cause a massive short circuit if a live wire comes in contact with it or is even buried in it. It will trip a GFCI but not a non-GFCI breaker. This is why antenna towers that are set in concrete always have a grounding wire connecting the tower to a ground rod next to the concrete base.
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Post by the light works on Nov 21, 2014 16:27:17 GMT
A couple of points. First, the second anode voltage of an old B&W TV was around 15,000 Volts. This will give you a nasty jolt even if you aren't grounded. While that's a pretty high voltage, it is limited to relativity low current. Enough to knock you on your butt, but probably not enough to kill you instantly. Second. Yes, concrete is conductive but conductivity is relative. It's not a very good conductor. It has a low enough resistance to give you a good shock if standing on it in your bare feet and you touch a live 120 or 240 volt wire, but not conductive enough to cause a massive short circuit if a live wire comes in contact with it or is even buried in it. It will trip a GFCI but not a non-GFCI breaker. This is why antenna towers that are set in concrete always have a grounding wire connecting the tower to a ground rod next to the concrete base. I've been hit by an HO fluorescent ballast before, which I believe has a starting impulse in the neighborhood of 7000V it was enough to cause involuntary muscle reactions; but I don't think it was fatal. a concrete encased electrode must be 20 feet long to have the same rating as two driven rods 8 feet long - with that said, a 2000 square foot slab foundation may still not pass enough current through the earth to trip a 15 amp circuit breaker. that is why swimming pools must have all bits of metal connected with copper bonding conductors. - for a low impedance equipotential bonding grid. I've also heard of a slab on grade foundation with an impermeable membrane under it essentially becoming a giant capacitor.
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Post by GTCGreg on Nov 21, 2014 16:33:49 GMT
A couple of points. First, the second anode voltage of an old B&W TV was around 15,000 Volts. This will give you a nasty jolt even if you aren't grounded. While that's a pretty high voltage, it is limited to relativity low current. Enough to knock you on your butt, but probably not enough to kill you instantly. Second. Yes, concrete is conductive but conductivity is relative. It's not a very good conductor. It has a low enough resistance to give you a good shock if standing on it in your bare feet and you touch a live 120 or 240 volt wire, but not conductive enough to cause a massive short circuit if a live wire comes in contact with it or is even buried in it. It will trip a GFCI but not a non-GFCI breaker. This is why antenna towers that are set in concrete always have a grounding wire connecting the tower to a ground rod next to the concrete base. a concrete encased electrode must be 20 feet long to have the same rating as two driven rods 8 feet long - with that said, a 2000 square foot slab foundation may still not pass enough current through the earth to trip a 15 amp circuit breaker. that is why swimming pools must have all bits of metal connected with copper bonding conductors. - for a low impedance equipotential bonding grid. When they put our pool in, not only was all the exposed metal, such as the ladder, step railing, and slide supports tied to a driven ground rod, but all the reinforcement mesh (remesh) buried in the concrete was also bonded together and connected to the rod.
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Post by the light works on Nov 21, 2014 16:35:43 GMT
a concrete encased electrode must be 20 feet long to have the same rating as two driven rods 8 feet long - with that said, a 2000 square foot slab foundation may still not pass enough current through the earth to trip a 15 amp circuit breaker. that is why swimming pools must have all bits of metal connected with copper bonding conductors. - for a low impedance equipotential bonding grid. When they put our pool in, not only was all the exposed metal, such as the ladder, step railing, and slide supports tied to a driven ground rod, but all the reinforcement mesh (remesh) buried in the concrete was also bonded together and connected to the rod. I've also heard of dairies developing voltage gradients and needing equipotential bonding.
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Post by GTCGreg on Nov 21, 2014 17:01:40 GMT
I've also heard of dairies developing voltage gradients and needing equipotential bonding. Well, if I got connected to one of those electric milking machines, I'd sure want everything at equipotential too.
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Post by silverdragon on Nov 22, 2014 9:25:20 GMT
No not bare wires, and 10guage as well (Domestic shower 45 amp rated) that thick because I didnt want it breaking, as I know I wont be replacing it.... all it does is run a weatherproof extension to the other side of the pond for secondary pumps. (Above water level sockets... I aint that daft...)(No honestly, I really aint that daft...) we could never get away with running a 45 amp load on a #10 conductor over here - that would take at least a #8. (although part of this is that our code automatically derates smaller wires for common installation conditions.) and it can be good to oversize conductors for motor loads. makes the motor happier and it runs more efficiently at full voltage. You may have a slight translation problem... 8mm is smaller than 10mm, What I call 10 gauge is 10 mm, or one cm thick over here....
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Post by the light works on Nov 22, 2014 11:59:01 GMT
okay, so your 10 gauge wire is actually 10 mm wire which is actually 8.36 square mm; which corresponds to 8 gauge wire.
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Post by GTCGreg on Nov 22, 2014 15:04:32 GMT
okay, so your 10 gauge wire is actually 10 mm wire which is actually 8.36 square mm; which corresponds to 8 gauge wire. I understand how it got it's origins, but our wire gauge system always seemed a little strange to me. An 8 gauge wire is thicker than a 10 gauge wire but a #8 bolt is smaller than a #10 bolt. Same kind of oddity is used in designating tubing sizes in refrigeration and plumbing. 3/4" copper tubing used by a refrigeration tech would be exactly the same size as 5/8" tubing used by a plumber.
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Post by Cybermortis on Nov 22, 2014 15:11:49 GMT
This may be interesting but is also off topic - CM.
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Post by silverdragon on Nov 24, 2014 8:55:36 GMT
Not so sure Cyber... if it concerns the wire used, "Bell wire", that really thin stuff, would just pop and burn out... you would have to have the right gauge wire to make the connections....?...
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Post by the light works on Nov 24, 2014 15:15:10 GMT
Not so sure Cyber... if it concerns the wire used, "Bell wire", that really thin stuff, would just pop and burn out... you would have to have the right gauge wire to make the connections....?... at that voltage, bell wire will have no trouble carrying enough current to cause fibrillation.
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Post by GTCGreg on Nov 24, 2014 15:20:04 GMT
Not so sure Cyber... if it concerns the wire used, "Bell wire", that really thin stuff, would just pop and burn out... you would have to have the right gauge wire to make the connections....?... I think Cyber's remark was aimed more at my comment about tubing sizes which had nothing to do with the topic. As for the wire, at the very small currents involved, almost any size wire would do the job. And you would have to figure that the guy connecting the TV to the table would use whatever wire was readily available, such as a piece of extension cord, which would be more than adequate size wise. EDIT: TLW beat me to the punch while I was posting.
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Post by the light works on Nov 24, 2014 15:23:28 GMT
Not so sure Cyber... if it concerns the wire used, "Bell wire", that really thin stuff, would just pop and burn out... you would have to have the right gauge wire to make the connections....?... I think Cyber's remark was aimed more at my comment about tubing sizes which had nothing to do with the topic. As for the wire, at the very small currents involved, almost any size wire would do the job. And you would have to figure that the guy connecting the TV to the table would use whatever wire was readily available, such as a piece of extension cord, which would be more than adequate size wise. EDIT: TLW beat me to the punch while I was posting. we'd all drifted. [/tangent]
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Post by silverdragon on Nov 25, 2014 9:13:20 GMT
I know one strand can cause shock, but we are looking into a circuit that has already made contact through the gun to earth, so current is flowing. I am thinking how long would that run before thin wire burns out.
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Post by the light works on Nov 25, 2014 15:00:28 GMT
I know one strand can cause shock, but we are looking into a circuit that has already made contact through the gun to earth, so current is flowing. I am thinking how long would that run before thin wire burns out. are you assuming the circuit is grounding through the table, or are you assuming the gunman is conductive enough to carry enough fault current to overheat the wire?
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Post by Lokifan on Nov 25, 2014 23:17:38 GMT
I'm assuming the gun is not already grounded. It only becomes grounded when the gunman touches it.
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Post by the light works on Nov 26, 2014 2:01:16 GMT
I'm assuming the gun is not already grounded. It only becomes grounded when the gunman touches it. that was my thought, too - otherwise the TV would not work.
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Post by silverdragon on Nov 26, 2014 8:35:26 GMT
And this is where the idea gets busted. It a metal table, already touching the floor, and there is water on the floor.... probably touching the table... How does a Human create a better short circuit that is already there?...
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Post by GTCGreg on Nov 26, 2014 14:40:56 GMT
And this is where the idea gets busted. It a metal table, already touching the floor, and there is water on the floor.... probably touching the table... How does a Human create a better short circuit that is already there?... maybe the table had wooden legs or rubber feet on the bottom to keep it from moving. As the Borg would say, "Resistance is futile"
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Post by the light works on Nov 26, 2014 14:59:42 GMT
And this is where the idea gets busted. It a metal table, already touching the floor, and there is water on the floor.... probably touching the table... How does a Human create a better short circuit that is already there?... maybe they didn't pour the water all the way to the table.
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