regarding electrical safety.

[Mark S.]

I am just reading a chapter on safety around electricity.
Is this following scenario correct?

If i had a situation where i had a circuit powered by a large d.c. voltage supply from a battery. (Enough to cause a shock). I could strip the wire going from the negative side of the battery before it meets its first resistance and grasp the wire without any shock at all.


Thanks Mark S.

 

[stevez]

I would not bet my life on that .....

What you are describing might be the ideal situation. In real life there can be breaks in the conductor or at connection points, etc, that cause things to depart from the ideal situation.

 

[ericgibbs]

I am just reading a chapter on safety around electricity.
Is this following scenario correct?

If i had a situation where i had a circuit powered by a large d.c. voltage supply from a battery. (Enough to cause a shock). I could strip the wire going from the negative side of the battery before it meets its first resistance and grasp the wire without any shock at all.


Thanks Mark S.

In theory yes, but in practice I would never recommend that you try it.

If there is leakage to ground of the positive side of the battery system you could get a serious electrical shock, never mess with high voltage DC.

 

[Russlk]

You can grasp any wire as long as you don't complete a circuit. Birds land on high tension wires with no problem and you could also if you could get there without touching ground.

 

[ericgibbs]

You can grasp any wire as long as you don't complete a circuit. Birds land on high tension wires with no problem and you could also if you could get there without touching ground.

hi Russ,
In fact overhead cable repair men are lowered onto 'hot' high tension cables, using a helicopter.

 

[CheapSlider]

hi Russ,
In fact overhead cable repair men are lowered onto 'hot' high tension cables, using a helicopter.

Youtube High Voltage Cable Inspection (3'10") also Danger: High Voltage (newspaper article)


UK telephone exchanges* use positive earth. In which case it could be possible to get a shock by making contact with earth while holding the stripped negative wire.
It also depends the type of load this wire is connected to:- suppose it was an inductive load and the battery end became o/c ?


*Telephone Office - usually about 50V but can be 80V

 

[TheVictim]

When you start dealing with VERY high voltages things can get a bit weird. Electricity has mass and inertia. When it is moving under the impetus of extreme voltage it can (and will) ignore such things as insulators, Ohm's Law, and the fact there is no APPARENT path to ground. High voltage corona leakage can zip right past a suitable conductor to ground on its way to zap something 3 feet away that just happened to be in its path to ???.

 

[Leftyretro]

Until you gain experience and knowledge you should be very careful working on or around any voltage above say 60 volts. Even low voltage like 12 volt automotive circuits can burn you very very badly if you short out a circuit with say a finger ring or metal watch band. The problem is that current and voltage are 'invisible' and there is no substitute for proper lock out tag out procedures and careful measurement before physically touching conductors.

Lefty

 

[TheVictim]

Shorting a watch band across a car battery would be extremely nasty.

 

[Thunderchild]

the situation is analog for ac neutral but I would not bet on it the one time i measured the voltage between neutral and earth it was a few volts but supposed to be 0 also you have to be 10000000000000 % sure of the system you are dealing with

 

[Nigel Goodwin]

the situation is analog for ac neutral but I would not bet on it the one time i measured the voltage between neutral and earth it was a few volts but supposed to be 0 also you have to be 10000000000000 % sure of the system you are dealing with

No, there normally SHOULD be a few volts between earth and neutral, unless you're using a PME earth, in which case it's basically the same wire!.

 

[Hero999]

The only problem with relying on the neutral for protection is if there's a break in it the case will become directly connected to live!

 

[Thunderchild]

No, there normally SHOULD be a few volts between earth and neutral, unless you're using a PME earth, in which case it's basically the same wire!.

well as far as i remember the neutral is connected to and earth stake at the substation so if in theory there was 0 resistance between your own earth stake and that of the substation the neutral would in effect be earth but for saftey reasons and so forth we use a seperate earth else plugging something in round the wrong way (quite easy in italy as the plugs are symetrical and go in either way) would make the chasis of a washing machine live, aparently here in italy and old trick to get free power was to use the earth as neutal this bypassed half the meter and the power being used was not registered by the meter

 

[things]

haha, thats wierd "plug your washing machines in backwards and the case becomes live" hmmmm, thats nice and safe i wonder if it will spin backwards too?

 

[Thunderchild]

no it won't spin backwards else half washing machines in italy would, thats the reason for the seperate earth wire in theory we could use the neutral and connect it to the chasis but for safety reasons it's not a good idea, an italian plug is three pins in a straight line so unlike eglish plugs theres a 50/50 chance you plug it in one way or another but the motors always turn the same way

 

[TheVictim]

I discovered the hard way there is a ground loop between my refrigerator and ancient electric range...

 

[Hero999]

no it won't spin backwards else half washing machines in italy would, thats the reason for the seperate earth wire in theory we could use the neutral and connect it to the chasis but for safety reasons it's not a good idea, an italian plug is three pins in a straight line so unlike eglish plugs theres a 50/50 chance you plug it in one way or another but the motors always turn the same way

English plugs also have three pins so there's no chance of rev ersing the connections, some US plugs only have two connections but they're only used for appliances that don't require an earth connection so it doesn't matter.

Here in the UK the earth is normally bonded to the neutral where the electricity enters the building and the electricity meter always measure the current and power in the live so it doesn't make any difference if you connect your appliance from live to earth. Also most circuits have an RCD fitted which will trip out if an appliance is connected from live to earth.

 

[Nigel Goodwin]

Here in the UK the earth is normally bonded to the neutral where the electricity enters the building

This is a relatively recent method, called a PME earth - the older installtions have a seperate earth spike providing the earth for the house. Personally I prefer the earth spike method, it's likely to be safer when an idiot puts a JCB bucket through the underground cable!

 

[Thunderchild]

hehe like in italy if they dig up the road either you will loose the water or the electric for a few hours I only hope that they learn better with the recent advent of piped gas