What does Earth Bonding involve?

[JohnW2]

Bonding saving lives.

... in that case I still don't understand why you questioned what John wrote, where he said that, in his opinion, bonding should be the highest priority.

Under extremely unusual circumstances, bonding can, indeed, 'save lives' (although I suspect that, even if you had the necessary data, you would probably struggle to find examples of someone who had died as a result of absent/inadequate bonding). However, it's also worth reminding people that unnecessary bonding can, in some circumstances, theoretically put lives at risk.

Kind Regards, John

 

[John D v2.0]

sorry thought i replied, I think maybe I exaggerated a bit, but at the end of the day the only reason ADS is safe is that there is an equipotential zone, and the bonding is critical to that. You can mess around with RCDs all day long but they are only additional protection, the bonding is fundamental.
Of course the chance of the PME neutral going up above 50v has been debated at length here and the various hazards gone through in detail. But anyway the message to the OP is the RCDs are not magic and he should sort out the whole package to be safe.

 

[JohnW2]

.... I think maybe I exaggerated a bit, but at the end of the day the only reason ADS is safe is that there is an equipotential zone, and the bonding is critical to that.

I'm not sure that I really understand that statement. ADS will commonly be (correctly and satisfactorily) triggered by events which are totally unrelated to any extraneous-c-ps, in which case (main) bonding is surely not in any way relevant, let alone 'critical' - or am I missing something?

Kind Regards, John

 

[bernardgreen]

They are required to connect (thick!) cables to supply metal water and gas pipe.

No body asks why, when RCDs are in place, the bond cable is a thick cable ( typical 6 or 10 mm ) when 30 mA of Earth leakage will trip an RCD.

The reason may have something to do with the fact that the bond cables are not protected in any way against over currrent that could occur if the extraneous source has a very low impedance and the CPC "Earth" derived from the incoming Neutral is a few volts above or below the potential of the extraneous source.

If the impedance of an extraneous source is 0.1 Ohm ( such as a metal water supply network ) and there is a potential difference of 20 volts between Network Neutral and the True Ground then the current in the bond wire will be 200 amps.

A slight aside is the definition of the word extraneous = irrelevant or unrelated to the subject being dealt with.

 

[EFLImpudence]

Extraneous also means 'of external origin' which is more relevant.

Not sure about the rest of your post.

 

[bernardgreen]

Not sure about the rest of your post.

John Ward explains it in his video HERE

A screen shot from the video show why the RCD does NOT trip while the person is being electrocuted.

There have been numerous incidents of fires caused by high currents in undersized bonding cables and/or loose or undersize connectors in the bonding system

 

[EFLImpudence]

Yes, we understand that but -

No body asks why, when RCDs are in place, the bond cable is a thick cable ( typical 6 or 10 mm ) when 30 mA of Earth leakage will trip an RCD.

Why would they ask that? They are separate things.

The reason may have something to do with the fact that the bond cables are not protected in any way against over currrent that could occur if the extraneous source has a very low impedance and the CPC "Earth" derived from the incoming Neutral is a few volts above or below the potential of the extraneous source.

Why should that lead people to ask your question?

If the impedance of an extraneous source is 0.1 Ohm ( such as a metal water supply network ) and there is a potential difference of 20 volts between Network Neutral and the True Ground then the current in the bond wire will be 200 amps.

Which is why the bonding cable has to be a thick one - but that is also a different issue.

 

[bernardgreen]

Which is why the bonding cable has to be a thick one - but that is also a different issue.

How can the thickness of the bonding cable and the reason for it being that thick be a different issue when the title of this thread is :-

What does Earth Bonding involve?

 

[JohnW2]

No body asks why, when RCDs are in place, the bond cable is a thick cable ( typical 6 or 10 mm ) when 30 mA of Earth leakage will trip an RCD.

"No body" is surely a gross exaggeration, since the only person who would ask that question would be someone who had very little understanding of bonding and/or the role of RCDs?

A slight aside is the definition of the word extraneous = irrelevant or unrelated to the subject being dealt with.

I've always felt that it was probably not the right word for them to chosen but BS7671 gives a fairly clear definition of what it means by an "extraneous-conductive-part" - and it is conductors that satisfy that definition which need main bonding. I say 'non-ideal' since there are conductive parts which are 'extraneous' (per the dictionary meaning of 'of external origin') which are not extraneous-c-ps by BS7671 definition (and hence do not need to be bonded).

However, as I wrote yesterday, extraneous-c-ps (and hence main bonding) are essentially irrelevant to ADS (whether that be mediated via OPDs or RCDs).

Kind Regards, John

 

[JohnW2]

How can the thickness of the bonding cable and the reason for it being that thick be a different issue when the title of this thread is :- What does Earth Bonding involve?

It's got everything to do with the title of the thread, but nothing to do with RCDs (nor, as I keep saying, anything I can think of which is relevant to ADS).

Kind Regards, John

 

[bernardgreen]

It has to do with the fact that no matter how many protective devices are fitted there can be very high ( fault ) currents flowing through cables inside the building.

And there is nothing the average house owner can do to stop that current.

 

[JohnW2]

It has to do with the fact that no matter how many protective devices are fitted there can be very high ( fault ) currents flowing through cables inside the building. And there is nothing the average house owner can do to stop that current.

All very true, but they are all just inevitable and inescapable facts which do nothing to explain what bonding "involves". You appear to be addressing issues/questions which have not been raised/asked.

Indeed, given that your concern seems to be about the very high (fault currents) which could flow through bonding conductors inside a building, some people might even interpret what you are saying as an argument against having main bonding ('when required') - which obviously would not be an acceptable option. In the case of TN-C-S supplies, elimination of extraneous-c-ps (which is far from impossible, and quite probably is already the case with many a new build these days) is the only way of avoiding that risk, since it remove thes need for any main bonding.

Kind Regards, John

 

[John D v2.0]

the only reason ADS is safe is that there is an equipotential zone,

ADS will commonly be (correctly and satisfactorily) triggered by events which are totally unrelated to any extraneous-c-ps

Sorry just to clarify i said the only reason it's safe, not that the only reason the MCB or rcd could trip. and i mean ADS as an overall concept for protection which used to be called EEBADS and includes a lot more than an MCB.
https://professional-electrician.com/technical/automatic-disconnection-supply-ads/

 

[JohnW2]

Sorry just to clarify i said the only reason it's safe, not that the only reason the MCB or rcd could trip. ...

You did - but in what sense is ADS not 'safe' in the absence of an equipotential zone (bonding)?

... and i mean ADS as an overall concept for protection which used to be called EEBADS and includes a lot more than an MCB.

For the reason that I've been explaining in this thread, I never really understood how/why the 'EEB' and 'ADS' got joined together in 'EEBADS', since they appear to refer to totally different, and essentially unrelated, things. Did they perhaps mean "EEB and ADS" as being a 'package' of two things that both served to provide safety, even though the two things were essentially unrelated?

Kind Regards, John

 

[EFLImpudence]

It did include the word 'and'.