equipotential zone

[richardpy1]

Can someone explain exactly why when you are in the garden you are outside the equipotential zone. If the applicance is plugged into a house socket then the CPC is connected all the way back to the main earthing terminal.
Is it because there is less resistance between your feet and the ground compared to in the house when there are floor boards and therefore you may expereince more shock current in the event of a fault ? This doesn't see to have much to do with a "zone".
Help me out !

 

[andy]

risk of shock is increased

 

[richardpy1]

Andy could you please explain why...is it just the reduced impedance to earth ?

 

[ebee]

The earth in your garden could be at a different potential to the earth of your electrical supply.
Sounds strange that doesn`t it?
Unfortunately we do not live on a big thick metal plate that is highly conductive .
We live on highly resistive lumps of soil crunched together like a huge massive spiders web of high resistances which are paralleled and seriesed together in all sorts and very many combinations which, overall giving a low resistance to the general mass of earth (therefore impedance to AC) but higher resistances between one area (zone) and another.
Your home and all its pipework is connected to one earth system at one potential and you garden might be at another potential.

 

[richardpy1]

Andy I think I understand...the start point of the transformer (and therefore the doemstic earthing arrangement) is tied to earth but due to variations this could be a different potential to earth in the garden.

Nevertheless, as I said before, the CPC (from the mower) which conducts fault current away is tied to the MET and therefore "in the zone".
Looking at the other path of fault current (ie through a person and into the ground) what difference is there is standing on floor boards in a house and standing in the garden...neither of these surface is tied to the MET and so could be at a different potential to the star point ?
Hope this makes sense.

Richard

 

[Lectrician]

The idea is to create a cage where anything that is earthy and exposed will be at the same voltage during a fault. The way to do this is by connecting all earthy items together with a cable. This creates a very low resistance, and hence the voltage will be the same on all earthed metalwork.

A fault must clear within a certain time (0.4sec for sockets). During this 0.4 seconds, all metalwork will rise near to mains voltage. If you touch two items, there will be 0v between them, you have a good chance of surviving.

Outside, mother earth is going to have a high impedance to your CPC - and hence a good strong voltage between the two during a fault. Remember, 50v is considered the maximum safe touch voltage.

Too early in the morning - hope that makes a little sense.

 

[Qedelec]

On a lighter note, it has also been kown to rain in gardens, causing a nice path from the live conductor, through your body to mother earth. This is a rare occurence inside the house

 

[Adam_151]

On a lighter note, it has also been kown to rain in gardens, causing a nice path from the live conductor, through your body to mother earth. This is a rare occurence inside the house

It depends whether or not I've tried to DIY plumbing work...