# electric ?

Discussion in 'General Electronics Chat' started by Mathematics!, Feb 26, 2010.

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1. ### Mathematics! Thread Starter Senior Member

Jul 21, 2008
1,022
4
Ok , I got the privlege of working with a master electrician to wire my home.

I know the theory and how to rig electrical circuits and electronic circuits.
However one day rigging the house we didn't shut the power completly off
just working with live wires.....

He being very experience working doing this stuff for 30 years or so.
And we got into an argument.
I said it was ok to touch the green or white ground wires even if the wires are live because your at the same potiential and your not completing the circuit. (he agreed and I demonstrated)

But then I said if you are touching the black wire you are going to get shocked because this is at a different potiential and you are closeing the circuit from the hot to ground...etc

He disagreed and said I hold it all the time when doing electric work on 120vac. He said you just cann't hold the white/green ground wires and the hot black or red wires at the same time. ( I agree with getting shocked if you hold the two wires but what I don't agree with is just by standing on the ground and holding just the black you are completing the circuit so you should get shocked.)

So he demonstrated it by holding the hot wire to much my suprise nothing happened ... he finely convinced me to try it so I did.

We are both pretty expereniced in electrical things ( me the theory more so and low voltage electronic circuits ,PCB boards ...etc him high voltage power ...stuff)

But the theory would say that your completing the circuit and current should flow thru you zapping you.... (governed by ohms law)

120volts = current * human body resistance
I am not sure what the average human body resistance....

The only thing I can think of is that are bodies where providing enough resistance to limit the current into an exceptable range so we couldn't even feel it flowing thru us (and it was to small to hurt us )
Because if this wasn't true then ohms law would be for ****.....

Also we both had rubber shoes on would this provide enough resistance
to be almost like an open circuit or what this is bothering me.
If we took are shoes off would this be a different story. <--(we don't dare do this )

So is it because the rubber shoes are the defining factor ???
Because if you hold the white and black at the same time current will have less human body resistance to flow thru to get back to the ground wire.
But in the case of holding just one hot wire are human body resistances is increased + the rubber boot resistance...

This is all I can think of
Just need clarity to know for sure definitley not going to try it ....
But this is the only way I can see the theory working....ohms law ...etc

He did keep saying you just cann't ground your self and you will be alright with "120 vac"
But I thought we are on the ground to begin with <--you mean to tell me just having some little piece of rubber under you your ok?

Thanks for input.
But either way you are always on the grounded I am justing thinking that it is the amount of resistance you provide defineds weather your going to get shocked.... since holding the white and black at the same time the electricity will just have to flow thru your arms and not thru your whole body out your rubber shoes ....

Last edited: Feb 26, 2010
2. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
What matters in every case is being in simultaneous contact with conductors at different potentials. It can be two wires, or a wire and some grounded metal, like a water pipe or the ground itself.

Electrical safety involves always checking conductors with a meter to verify they are not charged. Always treat an exposed wire as if it were electrically hot.

Imagining that your skin might be dry enough, or the floor might be insulated enough can lead to a fatal shock. Handling a live conductor can easily lead to a fatal accident.

3. ### rjenkins AAC Fanatic!

Nov 6, 2005
1,015
69
I had a friend some years ago who used to work on live cables as part of his job.

The work was typically splicing new power feed cables (for factories or new housing estates etc.) into existing, live, underground systems.

The cables were the feeds to new substations and operated at 15,000V...

A contractor would dig a large hole around and under the cable involved, then the guys doing the work would line the hole with several layers of thick rubber matting.

He said they then worked on one conductor at a time with normal tools.

He asked me on a couple of occasions if I would be willing to help, but the though of 15KV was a bit too much for me, it's waaay beyond the usual 240V 'ouch!' level...

4. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
12
As long as your feet/body are isolated, you can place one hand behind your back and touch a live wire. But for someone with 30 years of experience, or anyone else, it's not very bright -- unless you measure brightness in lumens should you "accidently" light yourself up.

Jul 7, 2009
1,585
141
Undoubtedly, you and the electrician both know that it's electrical current through the body that is the killer -- and the current is determined by the associated resistance. If you're standing on an insulator, then no sensible current will flow to earth using you as a conductor if you touch the hot wire -- the resistance is orders of magnitude too high. This is simply basic electronics.

However, I agree with nomurphy that it's foolish behavior. Not because you're at risk of a shock when you do it correctly, but it's just too easy to accidentally touch a grounded object or make a slip some time if you repeatedly work this way. In many industrial settings, this would be a firing offense for violating safety procedures.

6. ### beenthere Retired Moderator

Apr 20, 2004
15,815
282
That seems to be a good note to bring this to an end.