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Post by Lokifan on Oct 22, 2014 6:46:52 GMT
Saw this film a few days ago. It was filmed and set in the 1950s. The plot is that a group of assassins invade the home of a family and set up a sniper rifle in the living room, intending to shoot the President when he makes an unscheduled train stop. The rifle is bolted to a table with metal legs. To further stabilize the table, it's screwed into the floor. One of the hostages is a TV repairman, who connects the plate lead of the high voltage supply to the table leg. Another hostage then spills a glass of water on the floor surrounding the table. The TV is turned on, and works normally. Finally, when one of the assassins grabs the rifle, two things happen: 1. He is electrocuted. 2. The gun begins firing. The doomed assassin is yanking the trigger as he's having a seizure. He spends several seconds emptying the rifle at the train station as he dies, apparently without conscious control. So, myths are: 1. Could you watch TV with a setup as described? 2. Would it be lethal as shown? 3. Would someone hold onto the gun for seconds, or fall/drop dead from the shock? My guess is no, maybe, and no. Testing #3 is probably not possible. Frank Sinatra played the lead villain, and did a good job of looking like a psychopath, by the way.  Here's the whole movie. The scene in question is at 1:09:15. |
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Post by the light works on Oct 22, 2014 19:10:07 GMT
I would have to set up an electrical diagram of the circuit to figure it out. basically, if it was connected in such a way that touching the gun completed a low impedance circuit from the plate lead through the gun, through the assassin, to the wet carpet, and back to the transformer that was generating the high voltage, 1 is possible. as for 2, it is kind of a tossup. the only time I've been hit with a high voltage shock of that nature it was a current limited situation - but it made me drop the cover I was putting on the fixture. physical results of shocks are always a "your results may vary" situation.
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Post by silverdragon on Nov 17, 2014 8:49:06 GMT
Which is bolted to the floor.... and will therefore "Earth".....
If the rifle is not part of the circuit, it wont be affected.
If the carpet is an insulator, water wont help, because the table is bolted through that to the floor.
Either you will get electrocuted by stepping on the carpet, or not at all, but the weapon is not directly connected to anything, so where is the "Short Circuit" when you grab the weapon?.... why aint you already fizzing because you stepped in the puddle?...
The video is non existent because removal due to third party copywrite infringements... whatever that means.
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Post by Lokifan on Nov 17, 2014 9:03:26 GMT
That's part of the issue. All I could think was that maybe the table was metallic, and therefore both gun and table were "hot". The water may have helped conduct through the wood to plumbing/ground wire/etc., but only when someone touched both the water and the table would the circuit be complete.
Here's another copy. Scene in question is at 1:10:15 or thereabouts. You have to click the little "youtube" symbol at the bottom and watch it at the site.
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Post by silverdragon on Nov 17, 2014 9:40:14 GMT
If the table is already earthed (Bolted down) I cant see how the water would have changed anything.
Nor can I see how standing in water would create e better circuit than that which already exists.... via the table legs "Bolted" to the floor.
Its a mix of carpet and wood floor.
Where there is one wire from TV to the leg, what is the other connection?... how is the circuit completed?....
If that is earth, then as it already existed through the table leg, why didnt it blow as soon as it was switched on?....
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Post by Lokifan on Nov 17, 2014 16:24:07 GMT
Normally, I'd agree with you. Heck, I think in most cases, that's the only reasonable explanation.
However...
Maybe the table, although bolted down, wasn't fully earthed. The wooden floor could have acted as an insulator. That would leave it floating at a high potential.
The water could have provided a high resistance short to ground. When the person touched both the table and water, they provided a lower resistance short to ground, causing current flow that was enough to kill him. He wasn't getting the full current, but enough to kill.
A long shot, but could it be possible?
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Post by silverdragon on Nov 17, 2014 23:20:44 GMT
What caused the short through the Gun... he wasnt touching the table?...
Will current run through the gun...?.. wouldnt that detonate the round?...
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Post by Lokifan on Nov 18, 2014 3:06:41 GMT
I'm assuming the table was metal covered with formica, and the support and rifle each had metal-to-metal contact, making the entire table and gun one big conductor.
As long as there was no path to ground, the table theoretically could be floating at hundreds or even thousands of volts. Without any current flow, there would be no heat to ignite the rounds.
When he touched the metal of the gun (the trigger or barrel), he completed the circuit, and either the rounds started cooking off or he started jerking the trigger while convulsing.
It's a long shot (no pun intended).
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Post by silverdragon on Nov 18, 2014 8:54:15 GMT
Table tops are not usually metal, they usually are wood.....
But I suppose it may have been a tin top table....
I can see so many things that were not explained here.
And that makes us wonder {science}"Why"?....
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Post by Lokifan on Nov 18, 2014 16:09:08 GMT
In reality, it's usually just a scriptwriter's plot point. A handwave to build tension in the film. However, also in reality, I remember when I was once working on a test system that was normally mounted in a rack with a special filtered power supply. This one was simply set on a work bench and plugged into the wall. I threw a switch, and suddenly received a nice 120V tingle from the chassis of the machine. Seems that the normal power supply had an isolation transformer built in. Under the right circumstances, in a certain configuration, it could deliver a wallop to the chassis completely unintentionally. In this case, one of the right circumstances was me completing the circuit with my body. I'm just glad it wasn't across my heart. The first time it happened, I had assumed I'd been careless while working on exposed circuitry. Only after the second jolt did I discover that I hadn't been touching the circuitry, just the case. I spent a while tracking down the exact cause (lack of the isolation transformer) and promptly installed one on all bench test areas. |
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Post by silverdragon on Nov 19, 2014 10:14:01 GMT
I was working testing PCB's, and was doing the power test, to see if the right circuits were doing the right things, I had a test rig set up to feed the inputs expected via a separate test rig.
One of the supervisors was watching over what I was doing, mainly 'cos he was bored, and we was chatting...
He was leaning on the blue earth mat we were all supposed to be earthed to by wrist strap, "Just in case"
Unfortunately, neither of us were aware, the board under test had a fault, I flipped the main power, and it earthed straight away. Through that mat.
The test bench has MCB's that sensed earth faults and isolated the whole station should a fault be found, as well as setting off a strobe light alarm.
I dont know what was worse.. getting 240v through my wrist strap, the look of "pfzwassat??>" on the supervisors face, as he was zapped as well, the jolt of a millisecond of zap, the strobe light suddenly flashing, the buzzer, or the immediate appearance of the medical guy on the run.....
Apparently we had both jumped about two foot diagonally way from the rig, followed by the pop of the MCB, and the alarm?.. we had 'woken up' the whole test room.......
That was the only time we had a board fault like that in the whole time I worked there.
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Post by the light works on Nov 19, 2014 15:53:00 GMT
I have, over the years, developed a reaction I call "cold copper syndrome." essentially, if I unexpectedly touch copper, I flinch as though I've just been shocked. while it can be a valuable defense mechanism when working live circuits, it can sometimes be comical - like when I unexpectedly brush a wire inside my truck.
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Post by Lokifan on Nov 19, 2014 16:07:47 GMT
Ain't that a lovely feeling when you hand suddenly starts acting on its own?  One second, it's resting on chassis. Next second, it's hovering over your shoulder, trying to fly backwards. I haven't got a whole lot of jolts in my time (I'm usually over careful), but they are memorable. The same shop I was in that had the "shocking" chassis had a few systems designed to test diesel locomotives. The power supplies were ones you learned to never work on with both hands, just in case. Heck, the dummy loads for that system were bathtubs full of salt water that had electrodes stuck in each end. When running a test, the water would sometimes boil. No one in our group ever got hurt, luckily. |
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Post by Lokifan on Nov 19, 2014 16:09:30 GMT
Just found another reason to test this idea. The film, "Suddenly", is in the public domain. Thus, the MBs could use it royalty free. Can you see Adam dressed up as Frank Sinatra? |
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Post by the light works on Nov 19, 2014 16:12:12 GMT
concrete is conductive at 120V. proven fact.
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Post by silverdragon on Nov 20, 2014 8:48:09 GMT
concrete is conductive at 120V. proven fact. Really?... This I dont understand. If its true, care to put that as a separate "Myth" in strange ideas or something?.... Reason why, I have buried wires in concrete, and they aint short circuiting?.... If I had known that, I would have done some more wrapping in isolation tape to be double sure they were safe.... |
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Post by the light works on Nov 20, 2014 15:12:06 GMT
concrete is conductive at 120V. proven fact. Really?... This I dont understand. If its true, care to put that as a separate "Myth" in strange ideas or something?.... Reason why, I have buried wires in concrete, and they aint short circuiting?.... If I had known that, I would have done some more wrapping in isolation tape to be double sure they were safe.... but they weren't bare wires, were they? we pull wires through steel conduit all the time - the concrete is conductive - it doesn't inherently compromise the insulation on the wires. the only thing that makes it a bad idea to bury wires directly in concrete is that it is bugger all difficult to replace them if they get damaged. but yes, concrete is conductive which is why our standard grounding (earthing) method for a new home is to clamp the wire directly to the rebar in the foundation. - of course, the side effect of this is if you touch a live wire while working sock-foot on a concrete floor, you will feel it. |
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Post by Cybermortis on Nov 20, 2014 21:38:02 GMT
Just found another reason to test this idea. The film, "Suddenly", is in the public domain. Thus, the MBs could use it royalty free. Can you see Adam dressed up as Frank Sinatra? I think they'd need more than one myth to warrant dressing up like that. Maybe take a look at other Sinatra films? The biggest problem is that MB are wary of doing electricity myths as a rule, simply because they are hard to do in a visually interesting manner. We've had this discussion before, but unless or until they can think of a safe and practical way to show the results of electricity myths I suspect that they will remain wary of looking too hard at them. |
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Post by silverdragon on Nov 21, 2014 8:55:47 GMT
Really?... This I dont understand. If its true, care to put that as a separate "Myth" in strange ideas or something?.... Reason why, I have buried wires in concrete, and they aint short circuiting?.... If I had known that, I would have done some more wrapping in isolation tape to be double sure they were safe.... but they weren't bare wires, were they? we pull wires through steel conduit all the time - the concrete is conductive - it doesn't inherently compromise the insulation on the wires. the only thing that makes it a bad idea to bury wires directly in concrete is that it is bugger all difficult to replace them if they get damaged. but yes, concrete is conductive which is why our standard grounding (earthing) method for a new home is to clamp the wire directly to the rebar in the foundation. - of course, the side effect of this is if you touch a live wire while working sock-foot on a concrete floor, you will feel it. 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...) |
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Post by the light works on Nov 21, 2014 15:07:18 GMT
but they weren't bare wires, were they? we pull wires through steel conduit all the time - the concrete is conductive - it doesn't inherently compromise the insulation on the wires. the only thing that makes it a bad idea to bury wires directly in concrete is that it is bugger all difficult to replace them if they get damaged. but yes, concrete is conductive which is why our standard grounding (earthing) method for a new home is to clamp the wire directly to the rebar in the foundation. - of course, the side effect of this is if you touch a live wire while working sock-foot on a concrete floor, you will feel it. 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. |
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