NO "earth" in 18th

[bernardgreen]

For discussion only, do not act on this

All the confusion about earth and bonding could be removed at a stroke in the 18th edition.

Re-name the MET as the Main Equipotential Terminal, ban the use of the term "earth wire" and replace it with the true description " Circuit Protective Conductor ".

Then the difference between "bonding" and earthing would dis-appear.

There would still be areas of isolated bonding with no connection, intentional, un-avoidable or accidental, to the MET

At the MET there would be label stating the source of the MET potential, ground rod as in TT, TN-C-S etc and the maximum potential of the MET above true ground.

Make it clear that at times the voltage of the CPC and therefore all bonded ( or as previously ) "earthed" metal work may not be at the same potential as the earth surrounding the house.


It really confused an "electrician" whose clamp meter showed erratic currents in the bond between the Main Earth Terminal and the water supply pipe. He had replaced the undersized bare tinned copper bond and had noticed a spark even though the isolator at the meter was open ( OFF ) At times these currents peaked at over an amp. ( I suspect the peaks were much higher but were averaged by the meter's sampling/damping period. He had at first thought the water pipe ( metallic ) was shorting to something underground. The old hand called out from the firm explained it to him and the slightly worried customer.

 

[ericmark]

So we would have an ambulant polarity? I suppose ambulant could replace earth or ground but at the end of the day it's the same thing.

I would agree earth or ground is confusing to the beginner. It seems the whole idea of a gradient is missed out. Friction generates static and this is discharged around the world so as a result earth polarity must vary. This is without man doing anything.

The point is the whole idea of earth is so when we step out of the house we don't get a shock.

I had a huge problem with a tower crane in Sizewell. There were 6 inch sparks coming from the hook to the re-bar of the building. And the whole crane was steel and well embedded into the earth it was purely caused by the wind. Clearly in this case the gradient was too steep but there was little man could do about it.

 

[EFLImpudence]

All the confusion about earth and bonding could be removed at a stroke in the 18th edition.

There is no confusion.
Some people do not understand it or look for problems which are not there.

Re-name the MET as the Main Equipotential Terminal,

It is not a Main Equipotential Terminal.
It is the Main Earthing Terminal of the installation.

ban the use of the term "earth wire" and replace it with the true description " Circuit Protective Conductor ".

Fair enough.

Then the difference between "bonding" and earthing would dis-appear.

The difference between bonding and cpc would replace it.

There would still be areas of isolated bonding with no connection, intentional, un-avoidable or accidental, to the MET

If there is isolated bonding then it is not necessary.

At the MET there would be label stating the source of the MET potential, ground rod as in TT, TN-C-S etc and the maximum potential of the MET above true ground.

If you want.

Make it clear that at times the voltage of the CPC and therefore all bonded ( or as previously ) "earthed" metal work may not be at the same potential as the earth surrounding the house.

Do we not know that?

It really confused an "electrician" whose clamp meter showed erratic currents in the bond between the Main Earth Terminal and the water supply pipe. He had replaced the undersized bare tinned copper bond and had noticed a spark even though the isolator at the meter was open ( OFF ) At times these currents peaked at over an amp. ( I suspect the peaks were much higher but were averaged by the meter's sampling/damping period. He had at first thought the water pipe ( metallic ) was shorting to something underground. The old hand called out from the firm explained it to him and the slightly worried customer.

After which they did understand.
The problem was lack of knowledge not the bonding.

It doesn't matter what anything is called.
As long as the term used is correct then we shall know what is meant.
If people continue to use the wrong term then no one can be sure what they are talking about.


Should a poster ask on the forum -
"Should I earth my metal bath?" The answer is always "NO".

Should a poster ask on the forum -
"Should I bond my metal bath?" The answer is "It depends".

So, using the correct word is of the utmost importance and must be determined before the correct answer can be given.


In an ideal world all pipework could be isolated by the use of plastic inserts where the pipe emerges from the ground and at all places where it contacts with a cpc (at boiler etc.) then no bonding would be necessary.
However, other extraneous conductive parts may not be able to be isolated.

Therefore the installation is made safer by a compromise.

The cpcs are there to ensure operation of the opd.
The bonding is applied to ensure there is negligible difference in potential.

The fact that the wires used are the same colour is of no consequence
(I have suggested before that different colours could be used but people would get it wrong so no point.
Perhaps that is why g/y is used for both.)
and connect various parts together and to the met is the stated compromise to make the installation safer.

It, in no way, reduces the difference between the two separate purposes.

 

[flameport]

All the confusion about earth and bonding could be removed at a stroke in the 18th edition.

Perhaps, but this depends on people actually using the latest edition.

Plenty of people, including so called 'electricians' still use information from the 15th edition - the one which encouraged green and yellow wires to be attached to pretty much any fixed metal item.

 

[dingodeano]

Then the difference between "bonding" and earthing would dis-appear.

Not as long as they are sheathed in same colour.

 

[ban-all-sheds]

For moving on only, do not discuss

 

[Electrifying]

Bernard, why stop there?

Why not do away with earthing all together..........and at the same time remove the requirement for bonding.

No more electric shocks and no more confusion for people who can't grasp the difference between earthing and bonding.

All you need is an isolating transformer at the service head and Bobs your uncle.

Or, maybe just don't bother to spike the centre point/neutral in the first place.

 

[Electrifying]

Deleted - double post

 

[bernardgreen]

Bernard, why stop there?
Why not do away with earthing all together..........

We have already, in most domestic installations the CPC does not earth, it neutralises. Only in TT with an effective ground rod does the CPC return to earth.

and at the same time remove the requirement for bonding.

It has been said that bonding prevents electric shock by ensuring all touchable metal in the same area are at the same potential. That is good, touching two bonded items will be safe. It is also said that un-necessary earthing increases the risk of electric shock because if the item is not earthed then there is no return path for the current so no effective second point of contact. The reason birds can perch on 11 kv overkead bare wires is that they have no second point of contact.

So does bonding really reduce the risk ? Not if one of the items bonded is also earthed because the bonding has now connected all the items to an earthed item, they are all earthed and do present a second point of contact that is the potential of the MET.

Ask yourself if there is a logical reason why some double insulated equipment with metal casing must not have the CPC connected to its exposed metal. With double insulation preventing the live or neutral making contact with the case the there is no need for the case to be connected to the CPC. If that was the reason the wording would be "there is no requirement to earth this appliance" but there has to be something else as the wording is almost always "this appliance MUST NOT be earthed".

Electric lawn mowers that have been earthed ( the CPC is connected to the metal work ) and give a tingle to the user and the gas meter readers who report getting noticable electrical shocks from the meters.

 

[bernardgreen]

It is the Main Earthing Terminal of the installation.

But is it connected to earth ? Only in TT systems, in most others it is connected to the neutral or an imported reference that in the absence of network faults is at a potential close to earth potential.


The chances of the MET being at a dangerous potential above earth is small but network faults ( often the result of metal theft ) can result in the MET raising to a dangerous high voltage relative to earth. The equipotential area reduces the danger of the elevated MET to almost zero for any person totally inside the equipotential zone. But equipment that crosses the perimeter of the equipotential zone is at risk as is any person crossing the perimeter. Using an outside water tap that has metallic pipe work bonded ( earthed ) to the MET would carry a risk when the MET voltage is elevated to a dangerous voltage above true ground. Electric shock in this situation will not operate the RCD.

 

[Electrifying]

Bernard, why stop there?
Why not do away with earthing all together..........

We have already, in most domestic installations the CPC does not earth, it neutralises. Only in TT with an effective ground rod does the CPC return to earth.

and at the same time remove the requirement for bonding.

It has been said that bonding prevents electric shock by ensuring all touchable metal in the same area are at the same potential. That is good, touching two bonded items will be safe. It is also said that un-necessary earthing increases the risk of electric shock because if the item is not earthed then there is no return path for the current so no effective second point of contact. The reason birds can perch on 11 kv overkead bare wires is that they have no second point of contact.

So does bonding really reduce the risk ? Not if one of the items bonded is also earthed because the bonding has now connected all the items to an earthed item, they are all earthed and do present a second point of contact that is the potential of the MET.

Ask yourself if there is a logical reason why some double insulated equipment with metal casing must not have the CPC connected to its exposed metal. With double insulation preventing the live or neutral making contact with the case the there is no need for the case to be connected to the CPC. If that was the reason the wording would be "there is no requirement to earth this appliance" but there has to be something else as the wording is almost always "this appliance MUST NOT be earthed".

Electric lawn mowers that have been earthed ( the CPC is connected to the metal work ) and give a tingle to the user and the gas meter readers who report getting noticable electrical shocks from the meters.

Yes, but you're missing what I said.

If we didn't reference the star-point to earth in the first place, then there would be no need for earthing anything and we wouldn't have to worry about bonding gas pipes etc that introduce earth potential.

Think shaver socket in bathroom - but applied to the whole installation.

 

[bernardgreen]

Yes I am fully aware of the many benefits of a totally isolated supply, ( isolated from ground ) and have specified such in some non domestic situtations.

But not cost effective in the domestic market. More cost effective to rely on the integrity of the network to keep the neutral intact.

Cost reduction is a major ( and some would say adverse ) effect in the way things are done today. In the old days the reliance for the earth terminal was on other forms of ground reference but cost cutting and modern materials, like plastic non conductive water pipes changed all that.

 

[EFLImpudence]

It is the Main Earthing Terminal of the installation.

But is it connected to earth ?

Yes. That is what we call the point where it is connected to Neutral therefore it is and somewhere it will be connected to the planet.

Only in TT systems,

But TT is not very good as an 'earth' nor at doing its job of allowing enough current to operate the opd.
Is TN-S not one long earth rod?
Is TNC-S not several earth rods?

in most others it is connected to the neutral or an imported reference that in the absence of network faults is at a potential close to earth potential.

That, though, is how we ensure adequate current to operate the opd.

The chances of the MET being at a dangerous potential above earth is small but network faults ( often the result of metal theft ) can result in the MET raising to a dangerous high voltage relative to earth.

As said, it's a compromise to achieve the highest level of safety.
We cannot cater for every possible eventuality in the world (earth).
What if the thief were to steal all your cpcs?

The equipotential area reduces the danger of the elevated MET to almost zero for any person totally inside the equipotential zone. But equipment that crosses the perimeter of the equipotential zone is at risk as is any person crossing the perimeter.

Would you rather we made outside perfectly safe and ignored indoors ?
It's a compromise. We cannot do everything.

Using an outside water tap that has metallic pipe work bonded ( earthed ) to the MET would carry a risk when the MET voltage is elevated to a dangerous voltage above true ground.

Wouldn't that only be the case if the pipe were unnecessarily bonded?
It should only have been bonded if it was already earthed (by the planet).

Electric shock in this situation will not operate the RCD.

Are you advocating the reintroduction of ELCBs 'as well'?

Edit - I do, of course, mean VOELCB.

 

[Electrifying]

What if the thief were to steal all your cpcs?

 

[bernardgreen]

What if the thief were to steal all your cpcs?

You would be aware of the damage to the electrics and, if sensible, not use anything electrical until repairs had been completed. You would not be so immediately aware of the theft of metal outside the house .

in most others it is connected to the neutral or an imported reference that in the absence of network faults is at a potential close to earth potential.

That, though, is how we ensure adequate current to operate the opd.

Is over current protection the best way to disconnect in the case of a fault to CPC or true ground ?

I say the answer is no, it is not tbe best way. Only if the fault current is high enough to trip the OPD will over current devices detect a fault to greound or CPC. A 6 amp MCB will not trip even if 1.5 Kw is being disipated in the fault.

Earth leakage detection ( difference between Live and Neutral currents ) detects faults to CPC or ground once the fault current reaches about 30 mA. It will trip when less than 7 watts is being disipated in the fault.

Would you rather we made outside perfectly safe and ignored indoors ? It's a compromise. We cannot do everything.

The outside water tap should be supplied by plastic pipe and earthed by an earth rod to prevent it importing an extraneous potential into the equipotential zone of the garden. (This is probably why using CPC earthed equipment is no longer recommended as it is perceived as a risk. It is a risk if the CPC is not at ground potential. If due to a fault the CPC is at a dangerous potential above ground then the use of CPC earthed equipment in the garden ( including the water tap ) will present a hazard of electric shock. As the CPC is not disconnected ( cannot be disconnected ) by any safety devices this potentially lethal situation will not be automatically removed.

Are you advocating the reintroduction of ELCBs 'as well'?
Edit - I do, of course, mean VOELCB.

I can see some value in a system that monitors the potential difference between the CPC and ground and when this difference becomes hazardous isolates the incoming supply and disconnects the CPC from the neutral to remove the hazard of a CPC at a voltage that creates a hazard. I accept that a CPC at 230 or more volts above ground is perfectly safe for anyone totally inside the equipotential zone of that CPC. Unfortunately the perimeter of the equipotential zone is seldom 100 % free of possible conductive paths to ground.

In an ancient stone built cottage the dampness in the walls introduces true ground potential into the equipotential zone and for these buildings, like farm buildings, a TT supply is required with the CPC connected to a good ground rod system.