I need an indepth explanation of potential equalization

[Nikolaj Gjedde]

I need an indepth explanation of potential equalization

 

[James]

In what context?

 

[Nikolaj Gjedde]

In what context?

Like, is earthing in general (The green wire) just a form of potential equalization. For instance when you connect the green wire to a terminal in a lamp, let's say, is this just potential equalization?

 

[James]

For most things, the earth wire holds the voltage a metal part at zero volts, if a live wire touched the metal, the current flows from live to earth and causes a high enough current to blow the fuse and thus disconnect the electricity

 

[telectrix]

Like, is earthing in general (The green wire) just a form of potential equalization. For instance when you connect the green wire to a terminal in a lamp, let's say, is this just potential equalization?

all the earth wires are connected to metal enclosures and back at the supply. this means that everything in the house that is earthed is at the same potential. (including metal utitiy pipes and the metal pipework inside the premises). shouls a L-E fault develop, alL this earthed and bonded equipment will rise to the supply (L) voltage for the duration of the fault, thus reducing the risk of a voltage potential across a living organism ( including the mother-in-law).

 

[Rockingit]

thus reducing the risk of a voltage potential across a living organism ( including the mother-in-law).

Yeah, that's always been the flaw with ADS. My former MIL had a touch voltage of 'spikey' for which the only additional protection measure was out of reach, although the maths worked out to be several time zones rather than the conventional 2.5m.

 

[7029 dave]

Who cares about MIL, they come and they go, well in my case 2down.

 

[DPG]

Like, is earthing in general (The green wire) just a form of potential equalization. For instance when you connect the green wire to a terminal in a lamp, let's say, is this just potential equalization?

It's important to know the difference between earthing and bonding. It can confuse people, even some electricians, especially since to bond something you would normally connect it to earth (but the same 'earth's as the rest of the electrical installation.

Hope that makes sense - struggled to get it into words!

 

[Rockingit]

Who cares about MIL, they come and they go, well in my case 2down.

Also!

 

[Simon47]

It's important to know the difference between earthing and bonding. It can confuse people, even some electricians, especially since to bond something you would normally connect it to earth (but the same 'earth's as the rest of the electrical installation.

Yes indeed.

It is the earthing that will mean a fault will disconnect the supply by blowing a fuse/tripping a breaker.

It is the equipotential bonding that will prevent any dangerous voltage gradients between "things a person could touch" during that fault.

And the fault could be outside of the person's property (e.g. a fault in the distribution cable in the street) - but the equipotential bonding should mean that while conductive parts within the property are "live" (to some degree or other), they are all still at the same voltage so a person touching two devices cannot get a shock.
This equipotential bonding thing has it's limitations - such as once you take things outside or into wet areas. E.g. you have a car on charge outside, there's a fault that makes your local equipotential zone become "live", but a person is stood on wet ground, and so they can get a shock from the car body - that is why there are some very specific requirements for car charging points now. There's a similar issue with an outside tap connected with copper pipe to the house plumbing.
But within the property, the bonding means that you should not be able to touch any two items at different potentials.

An interesting variation on this is in some electrical test labs. In some, the measuring station and the people in it are connected to the high voltage - and only an earth reference for the instruments is brought into it (and carefully protected/separated from the people). So the people are actually sat inside a conductive box at a high voltage - it's not the voltage that's a problem, it's only when there's different voltages present that a danger arises. It's the same thing that allows birds to sit on high voltage power lines.

 

[Dave OCD]

And there was me thinking birds had rubber feet. ?