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opan1
Post  Post subject: Electrical circuit closing through body  |  Posted: Tue Feb 07, 2017 6:29 pm

Joined: Tue Feb 07, 2017 6:24 pm
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Hello. I have a couple of questions.

1.) Hypothetical situation: If I touch a live mains wire (not a closed circuit, just one wire sticking from the socket) electricity is not going to flow through my body which is not grounding because I'm on the 4th floor on my building. So I would not get a shock, right? Then why can I use a neon bulb screwdriver for testing a live wire? It still requires an electric flow through the body...

2.) Imagine a barbecue meat fork with two prongs. When I was little I stuck one of those in a socket but I held it by the plastic handle, so I'm good. But what if I was holding the metal itself? Theoretically the circuit will close at the point where the prongs meet, we would have a short circuit and there will be no flow above that point. Is that correct? Also, if I was holding it by the exact place of the meeting prongs, only my fingers would get damaged and not the entire body, right?

I'm not an engineer soo... sorry for the stupid questions, but I'm curious :D Thanks.


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Pong
Post  Post subject: Re: Electrical circuit closing through body  |  Posted: Wed Feb 08, 2017 3:03 am
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Joined: Sat May 28, 2016 2:53 am
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1)

There's a fuzzy area between the TRUE/FALSE question of grounding. A bit of stray current leaks through the air, you might imagine as an invisible halo. Recall how electric motors work. The type of tester you have depends on that. I believe it exploits the large surface area of your body.

After years of work on live wires every fibre of my body cringes from the thought of making it a path. For general reconnaissance I'm more comfortable using a non-contact tester that senses alternating current through the air, and then for actual tests a two-lead tester off known ground.

On 4th floor of a building you can easily be grounded! It's not about standing on the grass outside. Rather think of it as "path to Earth". The electrical system "ground" includes a metal stake driven ideally into the earth water table, to ensure an excellent path to Earth. Current takes whatever happens to be the best path. A typical building includes plenty of excellent metallic paths. For example if anywhere a metal pipe touches a steel electrical box or conduit, then likely all the pipes are grounded. Then if anywhere one pipe touches metal ducting then likely all the air ducts are grounded too... including that metal heat register hidden under a steel filing cabinet... and so on. I've found nail-heads in walls and floors that for whatever reasons were great paths to Earth - probably better than dry pavement outside. The housings of appliances like baseboard heaters and stoves are normally grounded. So be aware.

2)

Yes, the barbecue fork provides a much better path than through your flesh - you're safe from electrocution. Yet you're still risking injury in this scenario: Most injuries to electricians aren't from direct electrocution but from what happens after something goes POP in your face. You'll involuntarily startle. Imagine you're standing on a ladder sedately working on a ceiling fixture with a utility knife... if an arc flash flicks your fingers like a firecracker you can't help convulsing away from it. Panic is extremely hazardous.

To your last question, no, in theory you can safely strip the insulation off a live conductor with your teeth and suck the metal, minding the above. Current passing through a good conductor like a steel fork won't affect your fingers gripping it. Like the eagle landing on a bare high-voltage wire.

I need to repeat that besides direct electrocution other things can go wrong. The fork tips could weld to the terminals. Or one tip, while the other melts so it can't complete the circuit. You could have a weak or intermittent connection producing intense heat. That's the time to panic and thoughtlessly place your sweaty left hand on the grounded washing machine.


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opan1
Post  Post subject: Re: Electrical circuit closing through body  |  Posted: Wed Feb 08, 2017 3:45 pm

Joined: Tue Feb 07, 2017 6:24 pm
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Thank you very much for the extensive answer, you explained it great. :)


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