Question about earthing

[EFLImpudence]

It seems to me that in the original post the person talking about an earth rod does not know the difference between earthing and equipotential bonding.

In the original post, that's true ...

... but with respect to the raising of the meter reader receiving a shock it became bonding.

The purpose of bonding is to keep ECPs at or about the same potential in a fault, the risk of someone being in contact with an ECP and mother earth at the same time is considered low hence why we don't need to bother ourselves with bonding the outside world.

That answers/solves/removes the 'problem', then.

I've never had a 'tingle' from the gas meter nor the outside tap.

 

[JohnW2]

I'm still of the chain of thought that it is up to the electricity supplier, where they provide an earth, to ensure it is at or about the same potential to mother earth to reduce the risk.

That is generally how it is when they install a supply. To expect them to 'ensure' that the situation never changes would be to expect them to ensure that no faults ever arise - which is clearly unrealistic. I suppose they could be required to incorporate devices that would kill the supply in the event of the potential of their supplied 'earth' rising appreciably above true earth potential.

However, no matter what was 'required' of them, I think that I would still want some equipotential bonding within my house, 'just in case' they did not live up to those requirements!

Kind Regards, John.

 

[Spark123]

Yes, main bonding in your own premises is required as I said before, to reduce the risk of getting a shock from simultaneously accessible exposed/extraneous conductive parts when a fault occurs.
I was getting at it being up to the supplier to ensure their earthing is about the same potential as mother earth for people touching ECPs outdoors.
Take metallic streetlights for instance, are these all TT? Does a dog get a shock when it wees on it?

 

[JohnW2]

Yes, main bonding in your own premises is required as I said before, to reduce the risk of getting a shock from simultaneously accessible exposed/extraneous conductive parts when a fault occurs.

Indeed - but, as I implied, if we had this guaranteed Utopia of the supplier 'being required to ensure' that the 'earth' they supplied was never at a dangerous potential relative to true earth, then there would be no need for the requirement for equipotential bonding within premises.

I was getting at it being up to the supplier to ensure their earthing is about the same potential as mother earth for people touching ECPs outdoors.

The terminology gets a bit confusing here, since the extraneous-conductive-part (as viewed from within the premises) IS, if left to its own devices, going to be at, or very close to, true earth potential - that's the very reason why it poses a potential risk. It's only when people start bonding electrical installations to it that there is any risk of it being substantially above truth earth potential - so it's all a bit of a vicious circle!

In any event, as I said before, I would be very surprised if the suppliers didn't do exactly what you say when they install supplies - I find it hard to believe they would provide a supply with an 'earth' which was, at the time of installation, at a possibly dangerous potential above truth earth. It's the 'ensuring that there will never be any faults' which is the unrealistic bit.

Kind Regards, John.

 

[Spark123]

Yes, main bonding in your own premises is required as I said before, to reduce the risk of getting a shock from simultaneously accessible exposed/extraneous conductive parts when a fault occurs.

Indeed - but, as I implied, if we had this guaranteed Utopia of the supplier 'being required to ensure' that the 'earth' they supplied was never at a dangerous potential relative to true earth, then there would be no need for the requirement for equipotential bonding within premises.

Yes there would, as I have said - main protective bonding is to protect you should a fault occur in your premises and raises the potential of exposed conductive parts up to close to mains voltage for up to 5 seconds depending on what type of circuit it is, by ensuring a minimal voltage between exposed/extraneous conductive parts in your premises.
If you didn't have main bonding and you start introducing earthy metalwork into the premises i.e. gas pipes rigged to an earth electrode then you can have mains voltage between an exposed conductive part and the gas pipe and whatever it connects to under fault conditions.

 

[JohnW2]

Indeed - but, as I implied, if we had this guaranteed Utopia of the supplier 'being required to ensure' that the 'earth' they supplied was never at a dangerous potential relative to true earth, then there would be no need for the requirement for equipotential bonding within premises.

Yes there would, as I have said - main protective bonding is to protect you should a fault occur in your premises and raises the potential of exposed conductive parts up to close to mains voltage for up to 5 seconds depending on what type of circuit it is, by ensuring a minimal voltage between exposed/extraneous conductive parts in your premises.

I don't think that you realise how literally and hypothetically I was speaking . If, per your Utopia, a supplier was required to provide an earth which was never at a dangerous potential above true earth (under any circumstances), that would mean they would have to provide an earth of negligible Ze (far lower than the impedance of the L supply conductor), so that an L-E fault within the installation could not raise the potential of it (hence of exposed-conductive parts in the premises) to a dangerous extent above true earth level.

However, that is obviously a hypothetical scenario which we will never see. The fact remains, however, that risks only exist because (as you explain) the supplier's earth is never going to be capable of ensuring that it's potential never rises, under any circumstances (including faults in the installation).

Kind Regards, John.

 

[bernardgreen]

There have been incidents where a "Power surge" caused by vandals stealing copper from a substation have caused fires in meter boxes.

The picture in this article

http://www.dailymail.co.uk/news/art...ters-called-71-homes-massive-power-surge.html

shows a meter that has smoke damage that looks to have come from a fire localised around the earth terminal on the cut out below the meter. Later on it mentions that the metal theft involved the neutral at the substation.

 

[bernardgreen]

Talking to a friend last night who many years ago chart recorded the voltage between his PME derived CPC and a ground rod. Most of the time it was close to zero ( from his memory less than 5 volts ) but there were frequent peaks of over 30 volts when the pumps in the village sewage pump station started. The pump station was at the time supplied from the local 230/440 three phase supply to 13 houses. The effect on supplies to those 13 properties resulted in a new 11 Kv supply being put in place to supply the station.

He and I both recall the difficulties that a bouncing neutral caused when two phases in the cable shorted and as a means to restore power quickly before digging up the High St the shorted conductors were both connected to the same phase in the electricity substation

 

[bernardgreen]

If, per your Utopia, a supplier was required to provide an earth which was never at a dangerous potential above true earth (under any circumstances), that would mean they would have to provide an earth of negligible Ze (far lower than the impedance of the L supply conductor), so that an L-E fault within the installation could not raise the potential of it (hence of exposed-conductive parts in the premises) to a dangerous extent above true earth level.

Or provide a means to detect that the "earth" supplied was no longer at a safe voltage relative to true ground and at that stage automatically open circuit all three conductors ( Live, Neutral and the now unsafe "Earth" )

May be the reason for having fuses in the neutral supply was to prevent high fault currents through domestic wiring when there was [1] a Neutral to Ground fault via a metallic water pipe ( connection to substation mid point via steel water mains ) and [2] an un-balanced load on the 3 phases in the area resulting in current in the network Neutral. Some of that Neutral current would take the parallel path via the domestic wiring, the N to E fault and the water mains back to the sub station midpoint ( neutral ) . Without a fuse in the Neutral that fault current could burn out domestic wiring.

NOTE to DIYers Since most water mains are now plastic and RCD's will operate on 99% of fault currents in Neutrals the fusing of the Neutral is in most cases not necessary and may in most cases increase the hazards

 

[JohnW2]

Or provide a means to detect that the "earth" supplied was no longer at a safe voltage relative to true ground and at that stage automatically open circuit all three conductors ( Live, Neutral and the now unsafe "Earth" )

Indeed - as I wrote a few posts back...

...I suppose they could be required to incorporate devices that would kill the supply in the event of the potential of their supplied 'earth' rising appreciably above true earth potential.

However, I imagine the main problem with that is that it could (depending on the sensitivity of the sensing, the speed of disconnection and the correct performance of consumers' protective devices) mean that the whole neighbourhood might be plunged into darkness as a result of an L-E fault in one consumer's premises.

Kind Regards, John.

 

[ebee]

How do we post a pic on here?