Conduit in Wall

[mentalmike]

I'm looking to replace some 1.5mm 3 core and earth for a light switch that has got the green goop problem. Currently the light switch has one 1.5mm twin and earth and 1.5mm 3 core with no earth in metal oval conduit that is in plaster - I think its around 16mm. I'm pretty certain that there is no way I can re-feed the new wire in as it looks tight and also shouldn't the cable should have room to breathe? What would be the minimum sized conduit that I should use to replace this with when using one run of 1.5mm t & e and 1 run of 1.5mm 3 core & e vertically over 850mm

 

[RF Lighting]

On something like a switch drop, if the cable will fit, you're good to go.

If the circuit is not currently RCD protected, then you must either do so or use something like flex sheild cable, or earthed conduit.


You *may* be able to earth the existing conduit, depending on it's type and it's condition

 

[mentalmike]

Arse - I know my upstairs lights and downstairs lights are using MCBs only the sockets have RCD protection. Also I'm quite sure that all the light switchs are fed with this metal conduit unlike the socket cables that are plastered in the wall.

So for this particular light its would be ok to use 22mm oval - when pulling out the old cable the outer sheath has scracthed quite deeply so no chance getting the new stuff in with whats currently there!

As to my other new found problem of the metal conduit - I think I'd rather just change the mcb's to rcd so I don't have to destroy a wall in everyroom in the house. Am I allowed to do a straight swap of mcb to rcd in the consumer unit or do I have to get a sparky to do that?

 

[Click-Sure]

This is the strange thing. As far as Part P is concerned you can replace damaged cable (I'd say greening constitutes damage) in a dwelling all day long, as long as its like for like and follows the same route.

You cannot however change the devices protecting the circuit, such as replacing an MCB for an RCBO, which you would need to do to comply with British Standard 7671:2008 (seventeenth edition).

So you're either between a rock and a hard place or you don't know about the new rcd protection issues (after all Part P still hasn't been updated to reference the new regs!)

 

[plugwash]

anyway if you are skilled enough to be doing your own wiring and you are the person controlling any work done on the propertly aren't you skilled enough to make sure that work avoids the wiring........

 

[Lectrician]

Changing cable like for like is also classed as maintenance, and as such you do not really need to bring the installation upto the 17th by introducing RCD protection.

1.0mm T+E is far smaller than 1.5mm T+E. What size are you using? 1.0mm is fine for the majority is domestic installations.