Flying leads and the regulations.

[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

 

[hermetic]

"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)."

this is a direct qoute from the BS 7671

 

[hermetic]

I have checked wikipedia (lols) and it's definitions and mine are not at variance all extraneous metalwork should be bonded AND earthed. A bonded non earthed "equipotential zone" is dangerous in that should a fault occur the potential of all the bonded meatlwork can rise above that of earth

 

[telectrix]

"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)."

this is a direct qoute from the BS 7671

what reg. no.is that?

 

[malcolmsanford]

Would you mind sharing where that is ?

Again even if it is an exposed conductive part you are earthing it not bonding it ........................

 

[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.