Electric shock

[Jabbajaws]

Hi All, l have been pondering this in my head for absolutely ages and need an answer, if possible, to help me grasp this subject.

I understand that a person receives an electric shock when touching both a live conductor 230V, and an earth/neutral conductor 0V at the same time, because the live conductor is chasing 0V to continue the electrical path.

Now as far as im aware, a high enough current 80-100mA would cause a person's nerves to contract, with them not being able to let go.

Now if a person was to touch a live conductor, with no earth/neutral return path, would that person recieve an electrical shock? The person touches the live conductor of 230V, yet has themself a potential of 0V, so in theory, some electric current should be able to pass between these two points.

WOULD THIS CAUSE THE PERSON TO RECEIVE AN ELECTRIC SHOCK, AND 'THROW THEM OFF' AS THERE IS NO EARTH/NEUTRAL RETURN PATH?

ALSO WITH THE SAME PRINCIPLE, WHY DOES ELECTRIC SEPARATION PROTECT A PERSON WHEN THE LIVE CONDUCTOR IS 230V, YET THE PERSON IS 0V?

All feedback welcome ppl.. .

 

[Adam W]

If the person were in contact with earth they may receive a shock as the current would flow back to the transformer via the general mass of earth.
If the person were not in contact with earth (eg dangling off a HV line) they wouldn't get a shock because there would be nowhere for the current to flow, as per Jirkoff's law - this is how birds manage to sit on power lines without getting killed to death.

Electrical separation works in a similar way - The transformer is not earthed (separated from earth), so if you touch live it doesn't have anywhere to go back to. The same would work with a supply transformer, but the centre point is earthed to keep the voltage stable.

 

[J Sabo]

As said above, the current needs to flow back to the transformer via the general mass of earth.

This is how Cable Jointers (like myself) manage to joint LIVE cables, using insulated gloves and/or rubber mats.

 

[GT1]

This is how Cable Jointers (like myself) manage to joint LIVE cables, using insulated gloves and/or rubber mats.

And the very large underpants for your huge testicles...!!
Hats off you to you my friend. Rather you than me. I wouldnt have the cahones.. !

 

[Jabbajaws]

Okay ppl, let me put a scenario to you.

Lets assume that l am working on an upstairs metal light fitting in a house. I am stood on a carpeted wooden floor so im insulated from earth.

Let's say that the metal fitting, has a fault on it and a line conductor is touching the metal fitting. THERE IS NO EARTH present within this metal fitting...

Obviously there is no return path via earth as there isnt one. By your own explanations, l will not recieve a shock.

So why do we earth metallic fittings? Is it so that the earth fault is detected, and the protective device operates protecting the circuit?

If the earth wasn't there at all, then l wouldnt recieve a shock unless l touched L-N together, or the fact that im stood on the general mass of earth, which in this scenario l arent, im upstairs and inslated remember...

Advice please ppl???

 

[ezzzekiel]

We earth fittings to provide a fault path which is low enough to create a high fault current needed to operate the protective device.

Standing on a carpet or not, if you touch live some current will flow, enough to kill maybe not but then again maybe.
Now can we guarantee that everyone remains fully insulated all the time - no, so we need to provide an alternative to disconnect the supply.

 

[c.boy]

The purpose of the earth is not just 2 stop you getting zapped!! Its also there to protect the cable!!! a fault could occur no earth melted cables,burnt down house some1 is in jail!!!!!!!

 

[pevvers]

as per Jirkoff's law

I bet Kirchoff is turning in his grave now...

 

[Adam W]

I bet Kirchoff is turning in his grave now...

LOL whoops I probably should have checked the name first.

 

[Mr Mark Sparks]

Okay ppl, let me put a scenario to you.

Lets assume that l am working on an upstairs metal light fitting in a house. I am stood on a carpeted wooden floor so im insulated from earth.

Let's say that the metal fitting, has a fault on it and a line conductor is touching the metal fitting. THERE IS NO EARTH present within this metal fitting...

Obviously there is no return path via earth as there isnt one. By your own explanations, l will not recieve a shock.

So why do we earth metallic fittings? Is it so that the earth fault is detected, and the protective device operates protecting the circuit?

If the earth wasn't there at all, then l wouldnt recieve a shock unless l touched L-N together, or the fact that im stood on the general mass of earth, which in this scenario l arent, im upstairs and inslated remember...

Advice please ppl???

we also earth so when you are working on the light in your senario
and your mother in law brings you a cup of tea
she passes it to you while leaning on the nearby radiator
thus providing an earth path frying you both

 

[pevvers]

LOL whoops I probably should have checked the name first.

It's not so much the mistake, it's the fact that you've called him "Jerk off"!!

 

[pushrod]

I bet Kirchoff is turning in his grave now...

and that Kirchhoff guy won't be too pleased either The original made me laugh though

 

[pevvers]

and that Kirchhoff guy won't be too pleased either The original made me laugh though

Nice spot mate, it's been a while since I've been at college!!

 

[pushrod]

Nice spot mate, it's been a while since I've been at college!!

I reckon his university rivals probably did call him "jerk-off" and NovusSparkus has inside information

 

[pevvers]

I reckon his university rivals probably did call him "jerk-off" and NovusSparkus has inside information

Maybe, maybe... But we shall never know!

 

[Des 56]

If the generated supplied power is via two insulated conductors(as they are)where lies the fault path to fry those testicles ?

It exists only because of earth connections made deliberately or accidentally

If the supply was kept well insulated from terra firma,no earth fault could exist

The possibility of the double fault problem is a main reason for making that earth shock hassard available to us,without the double fault, the shock hassard (live neutral excepted)would not exist

 

[Jabbajaws]

Thanks for all your input everyone. Things seem alot clearer...

 

[Jim The Fish]

We earth fittings to provide a fault path which is low enough to create a high fault current needed to operate the protective device.

Standing on a carpet or not, if you touch live some current will flow, enough to kill maybe not but then again maybe.
Now can we guarantee that everyone remains fully insulated all the time - no, so we need to provide an alternative to disconnect the supply.

I can second that, I managed to inadvertently re-energize a cooker circuit whilst replacing the cooker switch, i was wearing well insulated work boots and had one hand on the underside of a wooden stair case (hardly a decent return path!) when i grabbed hold of the 10 mm t&e supplying the cooker and promptly ended up on my sorry arse. Luckily no damage done, well not physical any how! But just proves that current will find way its way home even through the highest resistance paths.

 

[Jabbajaws]

This was my theory all along with the 'hold on' effect, where the earth return is completed and the 'throw off' effect where like with yourself, you were thrown because the live conductor was at 230V, you were at 0V, and there was no where for the current to go so it threw you off.

That's my theory anyway... Please tell me if im wrong...

 

[Jim The Fish]

Well i'm not sure if i was thrown off it exactly, my theory is that i didn't take enough current to lock me up so i was still able to let go but then when i did let go i just dropped to floor, it happened so quick and was such a shock ('cuse the pun) i don't really know what the hell happened all i know is that i've never felt anything that strong before, as there was no RCD on the board i have no idea what sort of current i was pulling (well it was defiantly less than 40A, thankfully), i'll rig up an ammeter next time i change the switch LOL