A bit of bondage!

[echoes]

 

[david911cockburn]

It appears that you need to ask yourselves two simple questions:
If an earthed extraneous-conductive-part comes into contact with an energised circuit conductor, will the circuit be disconnected within an acceptable time frame?
Would we expect to find any dangerous potential difference between two circuit protective conductors supplied via the same distribution system?

The answer to the first question should be yes and the second question should be no, given that your loop impedences are within acceptable parameters. Therefore even though we highlight two different funtions of safety earthing, both supplementary bonding conductors and circuit protective conductors perform both functions adequately.

Sheds - please put forward a precise technical arguement or you just appear to be a fool shouting his mouth off. If you call me an idiot because I say A+B=C it means nothing, if you call me an idiot for saying A+B=C because you can prove that A+B=AB, people will respect your opinion.

 

[bernardgreen]

It really is time that some idependent body sat down to decide what is needed in the way of earthing and / or bonding to ensure safety in all foreseeable fault and mis use situations.

It seems an "electrician" intentionally cut the bond between large stainless steel sink and the water pipes. ( Found by a plumber installing the sink ).

When asked to explain the "electrician" said the rules were that sinks were not to be bonded as that would create a route to earth if some one was touching the sink and a wet electric kettle and hence the person would get a bigger shock.

( Question. Why doesn't the metal tap to metal sink provide that route to earth. Possible rule book answer " It doesn't " )

Assuming the tap to sink connection is not conductive ( insulating washers would be needed ) then a faulty double insulated appliance placed anywhere on the metal sink ( assume two bowls and double drainer ) could make the sink live. ( impossible of course as double insulated items are safe, we know this from the rule book ). With no route to earth the RCD will not have any reason to trip

So we have a live sink and taps connected by metal pipes to the boiler where the metal work is earthed. So one hand on sink ( live ), one hand on tap ( earth ) and one foot in the grave ( ground ). A sensitive person and less than 30 mA means the RDC won't be tripping but the heart might be stopped.

 

[aptsys]

If an earthed extraneous-conductive-part comes into contact with an energised circuit conductor, will the circuit be disconnected within an acceptable time frame?

That is not what supplementary bonding is for, so in answer to your question - maybe.

 

[ricicle]

It appears that you need to ask yourselves two simple questions:
If an earthed extraneous-conductive-part comes into contact with an energised circuit conductor, will the circuit be disconnected within an acceptable time frame?
Would we expect to find any dangerous potential difference between two circuit protective conductors supplied via the same distribution system?

The answer to the first question should be yes and the second question should be no, given that your loop impedences are within acceptable parameters. Therefore even though we highlight two different funtions of safety earthing, both supplementary bonding conductors and circuit protective conductors perform both functions adequately.

Now I know you're taking the p1$$......

Please, in one paragraph, explain the purpose of earthing and then the purpose of bonding.

 

[holmslaw]

Mr midickissorecosisetfiretoit

Could you please look at this video below and give your considered opinion as to whether this man should be bonded to earth, and what about the helicopter?

http://www.youtube.com/watch?v=Ze07J8IbQfA

 

[bernardgreen]

give your considered opinion as to whether this man should be bonded to earth,

Would you bond yourself to earth if you had no option but to work on live circuits ? ( such as when a DNO engineer works on an incoming suppy cable )

The video relates to planned maintainance and does not involve a fault on the circuit.

 

[SgtTrojan]

Earthing... always a good talking point

I'm going to get a bumper sticker made because I am that sad.

"Earthing - Splitting hairs and losing teeth since 1882"

 

[flameport]

Earthing and bonding is not particularly complex, and the book which contains the correct information is this one:


While it is twice the price of that other publication, it has several benefits:
1. It has been written by people who actually have a good knowledge of the subject
2. It has 168 A4 pages of correct information, rather than 8 small pages of nonsense.
3. It doesn't contain hundreds of mistakes.

 

[david911cockburn]

Let's start at the beginning with the EAWR:
The EAWR only talks in terms of 'conductors' and 'circuit conductors', it tells us that "all conductors (other than 'circuit conductors') must be connected to earth.
BS 7671 : 1991 simply expands upon the EAWR, it subdivides 'conductors' into two catergories; Exposed-conductive-parts and Extraneous-conductive-parts. It then gives us a set of 'loop impedence' figures and we are told that if we stay inside the parameters of the 'loop impedence' values, any fault currents that occur will be unable to reach such a magnitude for a sufficient duration of time to cause death or serious injury.
This theory is known as 'Earthed equipotential bonding and automatic disconnection of supply', it requires both 'circuit protective conductors' to supply an earth to fixed and portable electrical appliances (that may have exposed-conductive-parts) and 'supplementary bonding conductors' to supply an earth to 'conductors' that do not form part of the electrical installation (extraneous-conductive-parts). Therefore all 'conductors' that may be simultaneously accessible are connected to earth via the same earthing system, no two points of which should have a resistance between them that will allow a potential difference of greater than about 50v if a fault directly to earth should occur, because no matter which 'conductor' (exposed or extraneous) has become hazardous live having come into contact with a 'circuit conductor', we have supplied a low resistance earth path which will allow enough cuurent to flow to the mass of the earth quickly enough for the over-current protective device to disconnect the circuit within a specified time.
At the time the fault occurs the entire earthing system will become live for a moment but the fault current will be on its' way to the mass of the earth, therefore anybody who is in contact with an earthed 'conductor' will only be in parallel or 'indirect contact'. Anybody who is in simultaneous contact with two 'conductors' will only receive a shock of less than about 50v before the supply is automatically disconnected.

Compare the above to leaving 'conductors' not connected to earth:
If an un-earthed radiator comes into contact with a damaged 'circuit conductor', the radiator will simply become and remain 'hazardous live', anybody who touches the radiator (or any of the radiators if the water in the system is old) will become a series, high resistance path to earth and unless the shock exceeds 30mA (which is unlikely indoors) there is no reason why the supply should be automatically disconnected!

Summary:
Both 'circuit protective conductors' and 'supplementary bonding conductors' return 'earth leakage current' and 'earth fault current' to the mass of the earth, as long as 'loop impedence' readings are within given values, neither earth leakage current nor earth fault current will be allowed reach a magnitude or duration as to cause serious injury or death.

PS
The problem with the 16th Edition is that some definitions were taken straight out of the 15th Edition without being updated:
eg. Indirect contact - should have read;
Contact of persons or livestock with earthed conductive parts which have become live under fault conditions.

PPS
In between the EAWR 1989 & BS 7671 : 1991, a book was written called "The Electricity at Work Regulations 1989 An Open Learning Course 1990" by an outfit calling themselves THELA. This book is written in four sections, the first of which goes to great lengths to make sure the reader understands the difference between a 'conductor' and a 'circuit conductor'. Unfortunatey the other sections of the book appear to have been written by people who hadn't read the first section, as they go on to talk in terms of "electrical conductors" (a term which isn't used in Regulation 8 of the EAWR), as a result this book confused the living daylights out of everybody before the 16th Edition was even published.

 

[david911cockburn]

"It might disconnect the circuit" simply isn't good enough young man!

 

[aptsys]

^^ It doesn't have to. That is not the job of bonding - it is there to create an equipotential zone. The CPC's are there for disconnection of the supply.

 

[ricicle]

Let's start at the beginning with the EAWR:
The EAWR only talks in terms of 'conductors' and 'circuit conductors', it tells us that "all conductors (other than 'circuit conductors') must be connected to earth.
BS 7671 : 1991 simply expands upon the EAWR, it subdivides 'conductors' into two catergories; Exposed-conductive-parts and Extraneous-conductive-parts. It then gives us a set of 'loop impedence' figures and we are told that if we stay inside the parameters of the 'loop impedence' values, any fault currents that occur will be unable to reach such a magnitude for a sufficient duration of time to cause death or serious injury.
This theory is known as 'Earthed equipotential bonding and automatic disconnection of supply', it requires both 'circuit protective conductors' to supply an earth to fixed and portable electrical appliances (that may have exposed-conductive-parts) and 'supplementary bonding conductors' to supply an earth to 'conductors' that do not form part of the electrical installation (extraneous-conductive-parts). Therefore all 'conductors' that may be simultaneously accessible are connected to earth via the same earthing system, no two points of which should have a resistance between them that will allow a potential difference of greater than about 50v if a fault directly to earth should occur, because no matter which 'conductor' (exposed or extraneous) has become hazardous live having come into contact with a 'circuit conductor', we have supplied a low resistance earth path which will allow enough cuurent to flow to the mass of the earth quickly enough for the over-current protective device to disconnect the circuit within a specified time.
At the time the fault occurs the entire earthing system will become live for a moment but the fault current will be on its' way to the mass of the earth, therefore anybody who is in contact with an earthed 'conductor' will only be in parallel or 'indirect contact'. Anybody who is in simultaneous contact with two 'conductors' will only receive a shock of less than about 50v before the supply is automatically disconnected.

Compare the above to leaving 'conductors' not connected to earth:
If an un-earthed radiator comes into contact with a damaged 'circuit conductor', the radiator will simply become and remain 'hazardous live', anybody who touches the radiator (or any of the radiators if the water in the system is old) will become a series, high resistance path to earth and unless the shock exceeds 30mA (which is unlikely indoors) there is no reason why the supply should be automatically disconnected!

Summary:
Both 'circuit protective conductors' and 'supplementary bonding conductors' return 'earth leakage current' and 'earth fault current' to the mass of the earth, as long as 'loop impedence' readings are within given values, neither earth leakage current nor earth fault current will be allowed reach a magnitude or duration as to cause serious injury or death.

PS
The problem with the 16th Edition is that some definitions were taken straight out of the 15th Edition without being updated:
eg. Indirect contact - should have read;
Contact of persons or livestock with earthed conductive parts which have become live under fault conditions.

PPS
In between the EAWR 1989 & BS 7671 : 1991, a book was written called "The Electricity at Work Regulations 1989 An Open Learning Course 1990" by an outfit calling themselves THELA. This book is written in four sections, the first of which goes to great lengths to make sure the reader understands the difference between a 'conductor' and a 'circuit conductor'. Unfortunatey the other sections of the book appear to have been written by people who hadn't read the first section, as they go on to talk in terms of "electrical conductors" (a term which isn't used in Regulation 8 of the EAWR), as a result this book confused the living daylights out of everybody before the 16th Edition was even published.

TROLL

Admin: Please find out which of the regulars here is posing as this prat.

 

[david911cockburn]

Ricicle,
Be specific and present precise constructive criticism, or don't bother to speak.

What ever your name is,
If a circuit conductor comes into contact with the earthed steelwork of a building, how is the leaking current returned to the mass of the earth?

 

[aptsys]

If a circuit conductor comes into contact with the earthed steelwork of a building, how is the leaking current returned to the mass of the earth?

You wouldn't "earth" the steelwork of a building.