Flying leads and the regulations.

[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.

 

[telectrix]

comment has to be " why some poor sparky is prodding about inside an accessory with the circuit energised?"

 

[malcolmsanford]

"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.

Electrical bonding - Wikipedia, the free encyclopedia

Think you find that Tel as just explained it rather well in a sentence, and if your looking for a more in depth explanation this may help you.

 

[hermetic]

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.

 

[Deleted member 26818]

Yes we are quite aware that exposed-conductive-parts require earthing (not bonding).
However, whether a back box that is concealed in a wall, can be considered as exposed is debatable.
Irrespective of that, it is generally accepted that use of the socket plate fixing screws and a fixed lug provides the required earthing.

 

[malcolmsanford]

Well I think you will need to define exposed, a flush back box can only be touched when dismantling an installation so I would argue the point of that, as the installation should be isolated before any dismantling and so therefore technically it can not be come live, when it can be touched.

But apart from the semantics of exposed or not, you still do not bond it, you earth it, as you stated several times in your reply.............so your

"I would have thought that a fly lead to a back box was a perfect example of "earthed equipotential bonding"

Really isn't which is why I pointed it out, as it could cause confusion