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.. .

 

[martysparky]

DC makes you freeze like in the old films. AC alternates the current and the wave of alternation is what throws you off if it passes through your body. Probably why that type of current is used in a house etc.

If you touch the live conductor and get a belt it does not have to travel to earth via finger to foot. why because it can pass through part of your body. eg. up one finger down another or up one arm across your chest back to neutral at the ceiling rose/ cpc/ earthed/extraneous conductive par. think of the Megger tester safety test button to keep one arm away from the hazzard / danger.

basic stuff??

 

[Jabbajaws]

Thanx, everyone,

I must say im well chuffed with the response. I have learned so much about electric shock, merely by asking these questions and receiving advice from the experienced.

I will continue to monitor this topic, incase of any more feedback.

Many Thanks from JABBAJAWS...

 

[pushrod]

DC makes you freeze like in the old films. AC alternates the current and the wave of alternation is what throws you off if it passes through your body. Probably why that type of current is used in a house etc.

AC is widely used because of the ease with which it can be transformed from one voltage to another, so that it can be transmitted at very high voltages and small currents with consequent smaller power losses. It can then be stepped down easily to safer voltages for other uses, eg domestic etc.

 

[ezzzekiel]

also it comes quicker in the alphabet

 

[martysparky]

AC is widely used because of the ease with which it can be transformed from one voltage to another, so that it can be transmitted at very high voltages and small currents with consequent smaller power losses. It can then be stepped down easily to safer voltages for other uses, eg domestic etc.

Not so basic stuff

 

[kniteforce]

Your current is a bit off:
5 - 10 mA would throw you off with a painful sensation,
10 - 15 mA would cause your muscles to contract and you can't let go,
20 - 30 mA would impair your breathing and
50 mA would cause ventricular fibrillation and death.

This is why RCD's have a 30mA rating.



If there is no return path then there would be no current flow so the person wouldn't get an electric shock.

You can see this using a light bulb connected to the positive with a switch later in the circuit. While the switch is open (no return path) no current will flow and the bulb will not light. If the switch is closed (a return path) current will flow and the bulb will light.

20 odd years in the trade nd this subject still fascinates me and i can never conclusively answer it when asked!!

what confuses me even further is if 30ma rcds were inented to protct against ultimately,death,then why were 100 ma rcds ever fitted in domestic properties?? far too many questions!!

 

[Deleted member 26818]

killed to death.

As opposed to being killed almost to death?

 

[kniteforce]

As opposed to being killed almost to death?

loved that term as well!

 

[snowhead]

what confuses me even further is if 30ma rcds were inented to protct against ultimately,death,then why were 100 ma rcds ever made?? far too many questions!!

Or 300ma or 500ma or Rising rate or time delayed.

 

[pushrod]

20 odd years in the trade nd this subject still fascinates me and i can never conclusively answer it when asked!!

what confuses me even further is if 30ma rcds were inented to protct against ultimately,death,then why were 100 ma rcds ever fitted in domestic properties?? far too many questions!!

Or 300ma or 500ma or Rising rate or time delayed.

Larger rcds will help prevent the risk of fire through earth faults and time delayed ones allow discrimination when two are in series( I think, but happy to be corrected)

 

[ExArmy]

alot of theories getting branded about here...... please nobody try standing on a wooden staircase and touch a live cable, trust me you get a shock! i don't think you could put enough rubber mats between you and the floor to stop it either.

 

[Marvo]

....i don't think you could put enough rubber mats between you and the floor to stop it either.

Rubber mats work fine for live working as long as you also sheet off surrounding areas.
650V electrical safety matting, rubber safety matting 914-1220mm

 

[ExArmy]

Rubber mats work fine for live working as long as you also sheet off surrounding areas.
650V electrical safety matting, rubber safety matting 914-1220mm

in all http://www.google.co.uk/search?hl=e...SoOWWBw&ved=0CFYQvwUoAQ&q=seriousness&spell=1seriousness, i'd like to see someone sheet off the area, place down a rubber mat and then proceed to remove the db cover and grab hold of the busbar

 

[pushrod]

Rubber mats work fine

even rubber wellies are pretty good - my lad said to me "i'm barely getting a tingle when i touch your electric fence - that's not going to stop the fox with his thick fur getting to your chickens"
I said "try it without your wellies on"
30 seconds later "AAAARRRGGH !!!!"

 

[Adam W]

loved that term as well!

I suspect I got the inspiration from Top Gear: "For main course, lightly killed cow..." "We didn't have all this health & safety when I was a kid and nobody was even slightly killed..."

 

[Dave 85]

Interesting thread.
I've experienced plenty of electric shocks, most of the them, by touching a live wire, whilst standing on a carpet on a wooden floor, with trainers on. Always baffled me a bit.
Like exarmy said, I cant imagine anyone here would fancy standing on a rubber mat then touching a live buzzbar with a wet finger.

 

[Adam W]

Remember on a TT system we use 'the general mass of earth' (ie soil) as a return path. Soil isn't the best conductor hence why we use copper in cables and not soil, but it isn't the best insulator either, and when you add together the total mass (ie parallel paths) then you get a reasonable conductor.
Same with a house - you wouldn't use wooden cables because wood isn't renowned as a good conductor, but the whole floor, walls, plumbing etc of the house added together gives a significant return path.

If houses had earthed copper floors and you were standing on the floor with wet feet when you came into contact with a live part you may not get such a bad shock either because the protective device would operate before you noticed it, depending on the route the electricity takes through your body.

 

[i=p/u]

even when you have rubber shoes/slippers on and a live conductor touches your jumper , you still get a fizzel,

 

[Dave 85]

Remember on a TT system we use 'the general mass of earth' (ie soil) as a return path. Soil isn't the best conductor hence why we use copper in cables and not soil, but it isn't the best insulator either, and when you add together the total mass (ie parallel paths) then you get a reasonable conductor.
Same with a house - you wouldn't use wooden cables because wood isn't renowned as a good conductor, but the whole floor, walls, plumbing etc of the house added together gives a significant return path.

If houses had earthed copper floors and you were standing on the floor with wet feet when you came into contact with a live part you may not get such a bad shock either because the protective device would operate before you noticed it, depending on the route the electricity takes through your body.

Wouldn't fancy trying that one out on a 45 amp 3036

 

[Engineer54]

In the days of bus bar distribution for electrical supplies, it was common practice to have to drill the solid bars when all the provided holes had been filled. 9 times out of 10 these bars were drilled while still live, due to factory production etc!! I bet the HSE would have a pink fit and probably die in it, just thinking about it these days ...lol!!

Yes there was a procedure to be followed (of sorts), use of un-earthed drills, shortened drill bits, rubber mat(s), plastic swarf, collector, small rubber sheets wrapped around bars above and/or below, rubber gloves and full face/eye protection, ...and a guy with a big plank of wood standing by!! ...lol!! Still an apprentice the first time i had to do this and a second apprentice then made the connections...

I have no idea how anyone standing on bare wood, rubber mat, with rubber soled shoes can possibly get a belt from touching a 230/240 volt conductor, ...so where is the return path??

 

[StuSpiers]

In the days of bus bar distribution for electrical supplies, it was common practice to have to drill the solid bars when all the provided holes had been filled. 9 times out of 10 these bars were drilled while still live, due to factory production etc!! I bet the HSE would have a pink fit and probably die in it, just thinking about it these days ...lol!!

Yes there was a procedure to be followed (of sorts), use of un-earthed drills, shortened drill bits, rubber mat(s), plastic swarf, collector, small rubber sheets wrapped around bars above and/or below, rubber gloves and full face/eye protection, ...and a guy with a big plank of wood standing by!! ...lol!! Still an apprentice the first time i had to do this and a second apprentice then made the connections...

I have no idea how anyone standing on bare wood, rubber mat, with rubber soled shoes can possibly get a belt from touching a 230/240 volt conductor, ...so where is the return path??

It was much more fun If you didn't use swarf collectors.

I was that apprentice holding the plank of wood, when all of a sudden it was like bonfire night because of a wayward bit of swarf.

Those were the days.

EDIT:

Oh and I think the Sparks was more afraid I was going to crack him over the head than he was of a shorting piece of swarf!

 

[static zap]

Touching live will not always shock you , the danger arises while in the live condition you break the " 1 hand at a time advice ", and touch something earthed with the other hand - UP a ladder !

 

[needasparks]

in all seriousness, i'd like to see someone sheet off the area, place down a rubber mat and then proceed to remove the db cover and grab hold of the busbar

I worked with a guy who I did see doing up a live henley block with an alum key, was only on floorboards but his hands where like leather so no suprize.

 

[Jimmy Boy]

I use supposedly insulated steps they are all fibre glass with rubber feet and Ali treads, apparantly these are what electricians should use, not least I guess because Aluminimum is an excellent conductor, and you wouldn't want to swinging them around where potentially Live conductors might be.

Also can someone answer this question please.

We all know how an RCD works, and the human body can be treated as a large resistor, much like TF in a bulb, soooo..if I held the N and the L and was isolated form E would an RCD trip ? or would it just see me as an appliance ?
J

 

[pushrod]

I use supposedly insulated steps they are all fibre glass with rubber feet and Ali treads, apparantly these are what electricians should use, not least I guess because Aluminimum is an excellent conductor, and you wouldn't want to swinging them around where potentially Live conductors might be.

Also can someone answer this question please.

We all know how an RCD works, and the human body can be treated as a large resistor, much like TF in a bulb, soooo..if I held the N and the L and was isolated form E would an RCD trip ? or would it just see me as an appliance ?
J

Yep it should just see you as a not very clever appliance with a bit of a death wish

 

[Jimmy Boy]

LMAO..

I was just wondering if you were using a Class 2 Lawnmower with thick wellies on and you run the N and L through your fingers would it trip ?

J

 

[ExArmy]

LMAO..

I was just wondering if you were using a Class 2 Lawnmower with thick wellies on and you run the N and L through your fingers would it trip ?

J

depends on the breaker and how much current you pull. but probably not. assuming you are fully insulated from earth that is!

 

[Guest55]

We all know how an RCD works, and the human body can be treated as a large resistor, much like TF in a bulb, soooo..if I held the N and the L and was isolated form E would an RCD trip ? or would it just see me as an appliance ?
J

You'd be dead in the blink of an eye. Live in left hand , neutral in right hand , circuit would be completed round about where your heart is lol. ;-)

 

[pushrod]

You'd be dead in the blink of an eye. Live in left hand , neutral in right hand , circuit would be completed round about where your heart is lol. ;-)

Yeah and he would die unhappy as he wouldn't be able to check if the rcd had held

 

[Jimmy Boy]

So if a fault occurs on a Class 2 hand held appliance say from a frayed lead and the user is isolated from E an RCD is about as much use as chocolate condom ?

J