Flying leads and the regulations.

[steve snakeman]

can anyone tell me where in the 17th edition it tells you in black and white that you do not need a flying lead attatched to metal back boxes from a socket.Also the same for a steel sink in a kitchen.I have been reading it all day and have a sore head.Thanks.

 

[telectrix]

more to the point, where does it tell you that you have to bond kitchen sinks? sinks are not exranneous conductive parts unless the waste is metallic, in which case, the waste would need bonding. and it was back in the 16th, around 2003, trhat the need for flying leads was dropped as long as there was 1 fixed lug on the backbox. however, myself and a lot of other sparks prefer to fit a fly lead, if only to ensure that the backbox is earthed if the faceplate screws/pins are removed.

 

[steve snakeman]

Thanks for the reply.I am aware of all of the above and also put in a flying lead however I have been asked to a meeting on Monday where I have to prove my point .Another electrician tested a collegues work where no flying leads were present and listed them as class 1 faults on his condition report.I defended my partners work by explaning this and have been asked to prove it

 

[tony mc]

This is on the ESC website.

I would love to see what other code 1 observations were made if he classes this as Danger present Risk of injury.

So what did he do to elimanate that risk????????

[TABLE="class: mainblock"] [TR] [TD="class: sectiontitle"]SOCKET-OUTLET(S)

[TD="class: bigletter, width: 100"]S[/TD]
[TD="class: sectiontitle2, width: 100, align: center"]S181-5[/TD]

[TD="class: topictitle"]Earthing of enclosure (back box)[/TD]

Contents
1. Introduction

2. Where the cpc is a single-core cable or a core of a cable, connected directly into the earthing terminal of a socket-outlet
2.1 Metallic box with two fixed (non-adjustable) lugs
2.2 Metallic box with two adjustable lugs
2.3 Metallic box with one fixed and one adjustable lug

3. Where the cpc is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable


1. Introduction
Guidance is provided in this topic on whether it is necessary to install a so-called ‘earthing tail’ between a socket-outlet and an associated metallic back box. The guidance applies where protection against electric shock is by automatic disconnection of supply, as it is in the vast majority of cases.
A metallic back box for a surface-mounted socket-outlet is an exposed-conductive-part, and a metallic back box for a flush-mounted socket-outlet is deemed to be an exposed-conductive-part (even though it may not be able to be touched). Therefore, such back boxes, no less than every other exposed-conductive-part, are required to be earthed in accordance with Regulations 411.4.2 (TN systems) and 411.5.1 (TT systems) of BS 7671.
However, depending upon certain characteristics of the circuit protective conductor (cpc), the socket-outlet and its box, an ‘earthing tail’ may or may not be required between the socket-outlet and back box.

2. Where the cpc is a single-core cable or a core of a cable, connected directly into the earthing terminal of a socket-outlet
An earthing tail may not be required where the cpc associated with the circuit wiring from a distribution board to a socket-outlet takes the form of a single-core cable or a core of a cable, and is connected directly to the earthing terminal of the socket-outlet.
Whether an earthing tail is required depends upon whether one or both of the lugs on the back box are adjustable (to permit the socket-outlet to be levelled), and upon the earthing strap and eyelet arrangement of the socket-outlet, as detailed in items 2.1, 2.2 and 2.3.


[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD="align: center"]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD]2.1 Metallic box with two fixed (non-adjustable) lugs
The provision of an earthing tail is not required between a socket-outlet having an earthing strap and either one or two eyelets, and metallic back box as shown in Fig 1 (although the fitting of an earthing tail is still desirable). The box can be considered adequately earthed through the earthing straps and eyelets of the socket-outlet and the fixing lugs on the box.

2.2 Metallic box with two adjustable lugs
An earthing tail must be fitted between a socket-outlet and a back box having two adjustable lugs, such as the box shown in Fig 2. The need for this has been demonstrated where socket-outlets have suffered overheating and burning around the fixing holes due to a line-to-earth fault in metal boxes which had not been provided with an earthing tail. Because the adjustable lugs had become corroded, they presented a high resistance to the earth fault current, and consequently the circuit overcurrent protective device did not operate within the maximum time permitted by BS 7671. This resulted in a risk of electric shock as well as the thermal effects already mentioned.

Fig 1



[/TD]
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[TR]
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[TD="align: center"]
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[TR]
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[/TD]
[TD]
Fig 2


2.3 Metallic box with one fixed and one adjustable lug
Care must be exercised when installing back boxes having one fixed lug and one adjustable lug, as shown in Fig 3, because some socket-outlets have only one earthing strap and eyelet. It must be ensured that the earthing eyelet is located at the fixed lug position, otherwise an earthing tail must be provided.
Photograph courtesy of Legrand Electric Ltd.

Fig 3



3. Where the cpc is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable
Regulation 543.2.7 of BS 7671 requires an earthing tail to be fitted where the cpc associated with the circuit wiring from the distribution board to the socket-outlet is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable. The earthing tail must connect the earthing terminal of the socket-outlet to the earthing terminal incorporated in the associated back box (see Fig 4).

[/TD]
[/TR]
[TR]
[TD] [/TD]
[TD="align: center"]
[/TD]
[/TR]
[TR]
[TD]
[/TD]
[TD]An ‘earthing tail’ is required where the protective conductor is formed by metallic conduit, trunking or ducting, or the metal sheath and/or armour of a cable

Fig 4

The purpose of the earthing tail is not to earth the back box but to earth the socket-outlet (by connecting it to the back box).
The earthing of the back box itself is reliant upon the metallic conduit, trunking, ducting, or metal sheath or armour of a cable, forming the cpc. The requirements of BS 7671 relating to the use of such parts of a wiring system as a cpc are discussed in Topic P157-7.

[/TD]
[/TR]
[/TABLE]

 

[steve snakeman]

Thankyou very much.Oh and he did nothing as only a report was requested,personally anything I categorised as a class one I would not walk away from.

 

[telectrix]

This is on the ESC website.

I would love to see what other code 1 observations were made if he classes this as Danger present Risk of injury.

So what did he do to elimanate that risk????????

[TABLE="class: mainblock"] [TR] [TD="class: sectiontitle"]SOCKET-OUTLET(S)

[TD="class: bigletter"]S[/TD]
[TD="class: sectiontitle2, width: 100, align: center"]S181-5[/TD]

[TD="class: topictitle"]Earthing of enclosure (back box)[/TD]

Contents
1. Introduction

2. Where the cpc is a single-core cable or a core of a cable, connected directly into the earthing terminal of a socket-outlet
2.1 Metallic box with two fixed (non-adjustable) lugs
2.2 Metallic box with two adjustable lugs
2.3 Metallic box with one fixed and one adjustable lug

3. Where the cpc is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable


1. Introduction
Guidance is provided in this topic on whether it is necessary to install a so-called ‘earthing tail’ between a socket-outlet and an associated metallic back box. The guidance applies where protection against electric shock is by automatic disconnection of supply, as it is in the vast majority of cases.
A metallic back box for a surface-mounted socket-outlet is an exposed-conductive-part, and a metallic back box for a flush-mounted socket-outlet is deemed to be an exposed-conductive-part (even though it may not be able to be touched). Therefore, such back boxes, no less than every other exposed-conductive-part, are required to be earthed in accordance with Regulations 411.4.2 (TN systems) and 411.5.1 (TT systems) of BS 7671.
However, depending upon certain characteristics of the circuit protective conductor (cpc), the socket-outlet and its box, an ‘earthing tail’ may or may not be required between the socket-outlet and back box.

2. Where the cpc is a single-core cable or a core of a cable, connected directly into the earthing terminal of a socket-outlet
An earthing tail may not be required where the cpc associated with the circuit wiring from a distribution board to a socket-outlet takes the form of a single-core cable or a core of a cable, and is connected directly to the earthing terminal of the socket-outlet.
Whether an earthing tail is required depends upon whether one or both of the lugs on the back box are adjustable (to permit the socket-outlet to be levelled), and upon the earthing strap and eyelet arrangement of the socket-outlet, as detailed in items 2.1, 2.2 and 2.3.

[/TD]
[/TR]
[TR]
[TD][/TD]
[TD="align: center"][/TD]
[/TR]
[TR]
[TD][/TD]
[TD]2.1 Metallic box with two fixed (non-adjustable) lugs
The provision of an earthing tail is not required between a socket-outlet having an earthing strap and either one or two eyelets, and metallic back box as shown in Fig 1 (although the fitting of an earthing tail is still desirable). The box can be considered adequately earthed through the earthing straps and eyelets of the socket-outlet and the fixing lugs on the box.

2.2 Metallic box with two adjustable lugs
An earthing tail must be fitted between a socket-outlet and a back box having two adjustable lugs, such as the box shown in Fig 2. The need for this has been demonstrated where socket-outlets have suffered overheating and burning around the fixing holes due to a line-to-earth fault in metal boxes which had not been provided with an earthing tail. Because the adjustable lugs had become corroded, they presented a high resistance to the earth fault current, and consequently the circuit overcurrent protective device did not operate within the maximum time permitted by BS 7671. This resulted in a risk of electric shock as well as the thermal effects already mentioned.

Fig 1


[/TD]
[/TR]
[TR]
[TD][/TD]
[TD="align: center"][/TD]
[/TR]
[TR]
[TD][/TD]
[TD]Fig 2


2.3 Metallic box with one fixed and one adjustable lug
Care must be exercised when installing back boxes having one fixed lug and one adjustable lug, as shown in Fig 3, because some socket-outlets have only one earthing strap and eyelet. It must be ensured that the earthing eyelet is located at the fixed lug position, otherwise an earthing tail must be provided.
Photograph courtesy of Legrand Electric Ltd.

Fig 3



3. Where the cpc is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable
Regulation 543.2.7 of BS 7671 requires an earthing tail to be fitted where the cpc associated with the circuit wiring from the distribution board to the socket-outlet is formed by metallic conduit, trunking or ducting, or the metal sheath or armour of a cable. The earthing tail must connect the earthing terminal of the socket-outlet to the earthing terminal incorporated in the associated back box (see Fig 4).
[/TD]
[/TR]
[TR]
[TD][/TD]
[TD="align: center"][/TD]
[/TR]
[TR]
[TD][/TD]
[TD]An ‘earthing tail’ is required where the protective conductor is formed by metallic conduit, trunking or ducting, or the metal sheath and/or armour of a cable

Fig 4

The purpose of the earthing tail is not to earth the back box but to earth the socket-outlet (by connecting it to the back box).
The earthing of the back box itself is reliant upon the metallic conduit, trunking, ducting, or metal sheath or armour of a cable, forming the cpc. The requirements of BS 7671 relating to the use of such parts of a wiring system as a cpc are discussed in Topic P157-7.
[/TD]
[/TR]
[/TABLE]

trust the esc to turn a simple 4 line explanation into an essay

 

[steve snakeman]

just togive you a laugh I have been looking through his condition report and have just noticed this.....Hole in the wall where an extractor fan used to be ....requires further investigation?? That made me laugh.

 

[trev]

just togive you a laugh I have been looking through his condition report and have just noticed this.....Hole in the wall where an extractor fan used to be ....requires further investigation?? That made me laugh.

Maybe he didn't have time to look through the hole

 

[hermetic]

very interesting, a regulation that condones skimping, can anyone tell me what is achieved by not fitting a fly lead, apart from the saving of 100mm of copper and a bit of sleeving. I am really glad that I am not working day to day in domestic any more!

 

[aaelectric]

So isit required or not and what regs states it

 

[Deleted member 26818]

Perhaps he's going to get the Police to look into it?

 

[Geoffsd]

So isit required or not and what regs states it

No.

You cannot prove a negative.

 

[D Skelton]

very interesting, a regulation that condones skimping, can anyone tell me what is achieved by not fitting a fly lead, apart from the saving of 100mm of copper and a bit of sleeving. I am really glad that I am not working day to day in domestic any more!

About 3 mins labour per socket.

"Not much" I hear you say but when you're second fixing 30 dso's on a rewire, that's still two hours you could be spending on something else!

 

[albi1001]

If ever you are unsure about anything regarding earth connections always fit more than less. I have personally seen someone crossbond radiators and sinks in bathrooms when they know that the pipes under the floor are PVC fed. ****ing madness!!! I personally as a joke charged one of these radiators with a wind up generated high voltage (MEGA) and got a teenager to touch the radiator which was cross bonded (to pvc supply pipes). He jumped as high as the red bull he had been drinking prior to shock and seemed alert and even more keen & inquizitive to learn about electricity after his short sharp shock. Once i explained about the 17th edition regulations he said "well that clearly does not make any sense then, i'm back on my X-box". I personally cover everything i use in bathrooms with SELV and RCD or RCBO. "radiators do not need bonding but cross-bonding to all copper or metal fed piping & metal bathroom furniture"
Contact [email protected] for any chats...

 

[malcolmsanford]

543.2.7

" Where the protective conductor is formed by METAL conduit, trunking, or ducting or the metal sheath and/or armour of a cable, the earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure"

I underlined and made bold the only change from the original BS 7671.

So as to the regs the only time you need a fly lead in a box is when your using containment/exposed conductive part as protective conductor.

So though all the bodies ESC/NICEIC/GN notes advise that if there is not a fixed lug you should fit a fly lead on a T+E back box, it does not actually say so in the regs, and so if you are doing an EICR and found a non fixed lug box without a fly lead, should you code it ...............it is after all guides and advice say you should?

What would you do, and if you code it what would be the code, and why, and to what regulation.

 

[TaffyDuck]

very interesting, a regulation that condones skimping, can anyone tell me what is achieved by not fitting a fly lead, apart from the saving of 100mm of copper and a bit of sleeving. I am really glad that I am not working day to day in domestic any more!

I regularly nowadays come across back-boxes with one adjustable lug with no provision for a fly and they are passed to BS so I guess that says it all. Personally I fit them as a matter of course but Ive heard arguments saying you are more likely to create a problem by having 3 x cpc going into the earth on the back of a socket as its more likely to pull out than having 2. No way its a 1 on a PIR though, thats bonkers

 

[hermetic]

The above qouted is actually(or appears to be) guidelines, not regulations. The guidelines say that in certain circumstances, the tail can be omitted, and goes on to list those circumstances. Unfortunately it is very flawed. this statement:

"The guidance applies where protection against electric shock is by automatic disconnection of supply, as it is in the vast majority of cases"

made me laugh out loud, as RCD protection is by no means universal. It may exist in the "vast majority" of new buildings. but in the rest it is simply not there! The "vast majority" of the domestic and commercial properties I enter are over 15 years old, and generally still use rewirable fuse protection.

Basically what it says is you can omit a flylead if one of the socket front fixing lugs is fixed, or the box is earthed by SWA or metal conduit and a seperate earth or cpc is connected to the socket front, BUT ONLY IF THE WHOLE IS RCD PROTECTED!!
However, take the situation where some scumbag hasn't used a grommet in a metal box and the insulation is damaged. When sparky looking for a fault comes along and removes the socket front ,fault clears because the only earth on the box is via the screw, but the box remains live when he restores power to give the sparky a belt when he comes back to it! As I have said in my earlier post ommiting flyleads is just skimping. As professionals , and I am now speaking to the time served properly qualified amongst us, we are supposed to use the IEE regs plus our common sense and experience to produce an installation that is safe in all circumstances. If you need a regulation to back up everything you do,and look for regulations that justify doing less than what will be safe in every circumstance, you are not fit to call yourself an electrician

 

[Dave 85]

very interesting, a regulation that condones skimping, can anyone tell me what is achieved by not fitting a fly lead, apart from the saving of 100mm of copper and a bit of sleeving. I am really glad that I am not working day to day in domestic any more!

Personally I don't do it, never have, if BS7671 reckons it's safe, I'll go with that.

The fact is, as long as the faceplate is fitted correctly, the backbox is going to be earthed by the screws, if the plate is off, then the installation is not in a safe completed state anyway and anyone unscrewing a live faceplate should realise this and realise that if the live wire jumps out (which it won't) and lands on the now unearthed backbox, said box will give them a belt. If they don't realise this and they get a belt, well, they'll know for next time.

Fact is I do good work, I use gromets, do my screws up properly, always have RCD protection (in houses) etc one of my backboxes isn't just going to magically become live and kill someone.

For me, time is money, I work for myself I'm always busy, rarely get away from a job before 5pm and anything that can save me time without breaking rules or affecting finished quality, I embrace.

 

[hermetic]

Fair enough Dave 85, but if you re read my post you will see that I describe the conditions where the back box will be live, and it does not involve any wires jumping out. Some ppl will put up with a lowering of safety standards, some will not. I rarely if ever go back to my own work, it is usually the work of others that causes problems, and that is also the place where accidents happen to unwary sparks!

 

[hermetic]

Incidentally, Dave 85 if you NEVER do it, you are probably breaking guidlines in certain circumstances. BS7671 does not say you never need to fit a fly lead, it tells you under which circumstances you may omit a flylead. If the box has no flylead terminal, perhaps you are buying the wrong boxes for the circumstances, and perhaps this lowering of safety standards has been brought about by manufacturer lobbying in order to make box manufacture cheaper

 

[HandySparks]

Unfortunately it is very flawed. this statement:

"The guidance applies where protection against electric shock is by automatic disconnection of supply, as it is in the vast majority of cases"

made me laugh out loud, as RCD protection is by no means universal. It may exist in the "vast majority" of new buildings. but in the rest it is simply not there! The "vast majority" of the domestic and commercial properties I enter are over 15 years old, and generally still use rewirable fuse protection.

Basically what it says is you can omit a flylead if one of the socket front fixing lugs is fixed, or the box is earthed by SWA or metal conduit and a seperate earth or cpc is connected to the socket front, BUT ONLY IF THE WHOLE IS RCD PROTECTED!!

Are you saying that protection by "automatic disconnection of supply" requires an RCD?

Not true. ADS is the normal means of protection using rewirable fuses, MCBs, etc. See BGB 411.

 

[hermetic]

please quote the relevant passage of BGB 411 whatever that is, as I can find no online reference to it. A rewirable fuse is certainly NOT ADS as far as I am concerned, and if you read my above post, you would see that in the circunstances suggested a rewirable fuse would allow lethal current flow to occur. You are arguing a defenceless point because safety is reduced if the fly lead is omitted, and enhanced if it is fitted. Common sense says it should be there, the problem today is that too many regulations are unclear and conflicting, and common sense is anything but common. I would suggest if your profit margin depends on saving 30 minutes on an entire install by not fitting fly leads, you have misquoted for the job.

 

[HandySparks]

"BGB" is BS 7671:2008 Incorporating Amendment No.1: 2011, Requirements for Electrical Installations. Section 411, "Protective Measure: Automatic Disconnection of Supply".

You do have a copy, don't you?

 

[hermetic]

No, I don't, and never have had, I work to the IEE regs and ammendments, and as you will understand if you have read my above posts, I am not involved in day to day installation any more, so I have no need of one. Neither do I use regulations as an excuse for not thinking. What I do have is a five year apprenticeship at a NICEIC approved contractor from 1967 to 1972, a City and Guilds National diploma in electrical engineering (three years at tech college) and 40 years experience and the certain knowledge that if I had omitted fly leads in socket boxes I would not only have failed my first year at college, I would also have got my backside royally kicked at work. As I have said above, some people will put up with falling standards, some will not. If you have the relevant documentation, please quote from it. I have detailed above the circumstances in which the lack of a fly lead would make an instalation dangerous to an electrician investigating a fault, I stand by it.

 

[rich.250]

The above qouted is actually(or appears to be) guidelines, not regulations. The guidelines say that in certain circumstances, the tail can be omitted, and goes on to list those circumstances. Unfortunately it is very flawed. this statement:

"The guidance applies where protection against electric shock is by automatic disconnection of supply, as it is in the vast majority of cases"

made me laugh out loud, as RCD protection is by no means universal. It may exist in the "vast majority" of new buildings. but in the rest it is simply not there! The "vast majority" of the domestic and commercial properties I enter are over 15 years old, and generally still use rewirable fuse protection.

Basically what it says is you can omit a flylead if one of the socket front fixing lugs is fixed, or the box is earthed by SWA or metal conduit and a seperate earth or cpc is connected to the socket front, BUT ONLY IF THE WHOLE IS RCD PROTECTED!!
However, take the situation where some scumbag hasn't used a grommet in a metal box and the insulation is damaged. When sparky looking for a fault comes along and removes the socket front ,fault clears because the only earth on the box is via the screw, but the box remains live when he restores power to give the sparky a belt when he comes back to it! As I have said in my earlier post ommiting flyleads is just skimping. As professionals , and I am now speaking to the time served properly qualified amongst us, we are supposed to use the IEE regs plus our common sense and experience to produce an installation that is safe in all circumstances. If you need a regulation to back up everything you do,and look for regulations that justify doing less than what will be safe in every circumstance, you are not fit to call yourself an electrician

I have had that exact fault many times, haven't really got time for sloppiness.
Always grommets and tagged boxes, where no fixed lugs.
Most metal boxes I've come across recently don't even have earth terminals......
And as said previously they have the same bs number......

 

[HandySparks]

No, I don't, and never have had, I work to the IEE regs and ammendments, and as you will understand if you have read my above posts, I am not involved in day to day installation any more, so I have no need of one.

Sorry, I hadn't realised that you've been out of the game for a while.

The IEE Wiring Regs became BS7671 at the sixteenth edition. In that edition, the section I refer to is 413-02 "Protection by earthed equipotential bonding and automatic disconnection of supply", and in the fifteenth edition it's 413-2.

 

[hermetic]

Fine, mate, no problem, but I still can't see that a rewirable provides Automatic dissconection, I would want a circuit breaker for that, especially if it was me providing the live to earth path at the other end. As I have said, it is our responsibility according to the (old) IEE regulations to provide an installation that is a safe as it can be in all forseeable circumstances. I personally have never seen socket boxes without earth/cpc/connections, but in this day and age nothing really surprises me.Standards have been alowed to fall dramatically. Don't even get me started on part P!

 

[hermetic]

Also, he said carrying on(LOLS) I would have thought that a fly lead to a back box was a perfect example of "earthed equipotential bonding"

 

[telectrix]

Fine, mate, no problem, but I still can't see that a rewirable provides Automatic dissconection, I would want a circuit breaker for that,

the whole meaning of ADS is nothing to do with RCDs. it's disconnection of supply in the event of a fault. the impedance of the fault path dictates the time taken for the OCPD to operate, whether it be a MCB or a fuse. no OCPD will operate at the sort of level of current that will kill you, that's why we have RCDs AS ADDITIONAL PROTECTION. i do agree with you that fitting flyleads is good practice.

 

[hermetic]

"no OCPD will operate at the sort of level of current that will kill you, that's why we have RCDs AS ADDITIONAL PROTECTION"

Which is exactly what I have said! if there is no RCD, and in my experience installations over twenty years old, and there are millions out there, have no RCD, and will kill you if you become the fault path between an unearthed box that has become live due to insulation damage, and an earthed socket front, if the circuit is only protected by rewirables.

 

[i=p/u]

well we would fail conduit asessments if we didnt have fly leads added, even in all steel conduit circuits.. ...

 

[Geoffsd]

I still can't see that a rewirable provides Automatic dissconection,

automaticadjective (INDEPENDENT)

Definition

An automatic machine or device is able to operate independently of human control

 

[malcolmsanford]

Also, he said carrying on(LOLS) I would have thought that a fly lead to a back box was a perfect example of "earthed equipotential bonding"

In fact it is quite a poor example of bonding, as a fly lead in a back box is earthing

 

[rich.250]

Of course a 3036 rewritable will provide ads. If the circuit complies with the relevant zs for the device. Will still operate in the required time.

I also see a lot of Single boxes for switches with earths in a connector. I see this as worse than not tagging a socket!! Cos at least when the install is finished the screws are earthed.
There not if you don't earth the box on anything rated below ten amps
It Seems.........

 

[rich.250]

Rewirable. Stupid phone.

 

[hermetic]

"In fact it is quite a poor example of bonding, as a fly lead in a back box is earthing"

Please explain your understanding of the differences between earthing and bonding as they apply within an installation final sub circuit as opposed to at incoming supply connection.

 

[telectrix]

my interpretation is that you earth exposed conductive parts and bond extraneous conductive parts.

 

[hermetic]

Yes Rich250, I got your meaning, and you are quite correct that the rewiarable will blow in the case of a direct short type fault to earth depending on the Ze. However, if the fault path from a live untagged back box to earth is via the body of some poor sparky, sufficient current will flow to kill him without the fuse blowing, which was my initial premise. We have already had a comment to say that someone has seen this fault "many times"

 

[hermetic]

The guidance from BS given above says that although in most circumstances a back box cannot be touched it is still classed as "exposed" and therefore must be earthed.
Bonded to what? if not to earth then to other extraneous metalwork? what is the point of that? If it is not ultimately bonded to earth then its potential can rise above that of earth (be it a spike, pme, transformer tapping or whatever), hence the term Equipotential bonding. I agree fully with the point about switch boxes by the way.

 

[Deleted member 26818]

We are required to earth exposed-conductive-parts.
It is generally accepted that this earthing can be achieved by means of the 3.5mm screw and a fixed lug.
Where socket-outlet back boxes, are concealed in walls, they are not necessarily exposed.
Earthe Equipotential Bonding, or Main Protective Bonding (as it is now known) would only be required, if the socket-outlet back box is considered an extraneous-conductive-part.