Twin and Earth. (insulated earth)

[winston1]

522.5.2 Dissimilar metals liable to initiate electrolytic action shall not be placed in contact with each other,
unless special arrangements are made to avoid the consequences of such contact.

Metal backboxes are not made of copper but the copper earth wires are held in contact with them by a brass screw. Comments?

 

[JohnW2]

For the same reason, bare copper sheathed cables must not be installed on galvanised metalwork

Maybe, but we're not talking about "bare copper sheathed cables" - we're talking about the bare copper CPC within the PVC sheath of a T+E cable. Even if the PVC sheath were in contact with galvanised metalwork, there would be no problem with the CPC within it being 'bare copper'.

 

[donrkebab]

Metal backboxes are not made of copper but the copper earth wires are held in contact with them by a brass screw. Comments?

I know.

 

[donrkebab]

Maybe, but we're not talking about "bare copper sheathed cables" - we're talking about the bare copper CPC within the PVC sheath of a T+E cable. Even if the PVC sheath were in contact with galvanised metalwork, there would be no problem with the CPC within it being 'bare copper'.

Sorry for adding information that confused you, but a reasonable person could clearly understand my post.

That's why the first words were - Sleeving is required because: , for the benefit of johnw2, it didn't feel necessary to expand on those first words because the thread (or where I joined it) is about why earth wires need to be sleeved.

 

[rsgaz]

copper earth wires are held in contact with them by a brass screw. Comments?

He said dissimilar. Copper and brass are very similar! Approx ⅔ copper!

 

[bernardgreen]

Dissimilar metals liable to initiate electrolytic action shall not be placed in contact with each other,
unless special arrangements are made to avoid the consequences of such contact.

To have any action there has to be an electrolyte in contact with the dissimilar metals. Water ( other than pure de-ionised water ) will act as a mild electrolye, salt water is a powerful electrolyte,

 

[AndyPRK]

Sleeving the ends of cpcs came in around 1970. It was only green then.

 

[donrkebab]

To have any action there has to be an electrolyte in contact with the dissimilar metals. Water ( other than pure de-ionised water ) will act as a mild electrolye, salt water is a powerful electrolyte,

I imagine they were concerned about conditions created by newly applied damp plaster, and also that dried plaster remains hygroscopic.

 

[JohnW2]

He said dissimilar. Copper and brass are very similar! Approx ⅔ copper!

To be fair, winston was surely talking about the contact between the copper conductor and the steel backbox, wasn't he? - the 'brass screw' is only there to keep the copper (conductor) in good contact with the steel.

Kind Regards, John

 

[rsgaz]

Oops, I misread it, apologies winston.

 

[JohnW2]

... for the benefit of johnw2, it didn't feel necessary to expand on those first words because the thread (or where I joined it) is about why earth wires need to be sleeved.

Exactly, as you say, the thread is about the sleeving of earth wires (in T+E cables), and is therefore nothing to do with "bare copper sheathed cables".

The only situation in which the copper of the CPC of T+E cable comes in contact with a dissimilar metal is when that is done deliberately to establish an electrical connection (e.g. in a galvanised steel box, or to connect to (non-cuprous) exposed-c-ps of equipment) - and it's obviously essential that nothing is done to 'prevent' that contact of dissimilar metals.

 

[donrkebab]

Exactly, as you say, the thread is about the sleeving of earth wires (in T+E cables), and is therefore nothing to do with "bare copper sheathed cables".

The only situation in which the copper of the CPC of T+E cable comes in contact with a dissimilar metal is when that is done deliberately to establish an electrical connection (e.g. in a galvanised steel box, or to connect to (non-cuprous) exposed-c-ps of equipment) - and it's obviously essential that nothing is done to 'prevent' that contact of dissimilar metals.

As usual you've lost me between your nonsense and twisted logic. I don't know what you're on about.

But, as I have stated before, my post was relevant and quite understandable to anyone that wants to understand.

You have said "it's obviously essential that nothing is done to 'prevent' that contact of dissimilar metals.", quite bizarre.

 

[JohnW2]

You have said "it's obviously essential that nothing is done to 'prevent' that contact of dissimilar metals.", quite bizarre.

If you cannot understand why it is essential not to do anything to prevent contact between a copper CPC and the steel/aluminium/whatever exposed-c-p it is protecting, then I give up.

 

[donrkebab]

then I give up.

I'll drink to that, cheers

 

[Risteard]

Sleeving is required because:

522.5.2 Dissimilar metals liable to initiate electrolytic action shall not be placed in contact with each other,
unless special arrangements are made to avoid the consequences of such contact.

522.5.3 Materials liable to cause mutual or individual deterioration or hazardous degradation shall not be
placed in contact with each other.

For the same reason, bare copper sheathed cables must not be installed on galvanised metalwork

You have quoted the wrong Regulations.

There is a Regulation specifically and overtly requiring sleeving to be fitted. It's written in black and white. So yes - it absolutely is a Requirement.