Another question about potential re-wire ?

[ac1951]

Another question about potential re-wire. The existing wiring : Installed circa 1975 Power cables PVC 2.5mm twin and earth (solid not stranded conductors) Lighting cables are PVC double insulated singles with earth (again solid not stranded conductors)

I realise that these do not comply in terms of the new colour coding but in all other respects they seem perfectly OK. I'm planning to split the ring main into two (upstairs and downstairs) and add some additional sockets. Also make a similiar split in the lighting and I was hoping that I wouldn't have to replace all the existing wiring.

Does this sound feasable and would I get my relevant approvals...??

Andy

[TheScullster]

andy castledine wrote

Sounds perfectly feasible. If you are doing the work yourself you will need to do it on a building notice and have your local BCO check at first fix and also before final connection. You will also need to put a sticker on the CU to state that mixed colours are used. Presumably you will also be swapping the CU to expand your options now and later?

I have a 1973 property which is wired similarly. Provided the existing cable terminations have remained tight, the cable appears in very good condition.

Phil

[John Rumm]

You should. One thing worth checking is the size of the earth wire on the power circuits. Modern 2.5mm^2 T&E has a 1.5mm^2 earth wire. Some of the early 2.5mm^2 T&E cables only had a 1mm^2 earth. I would be wary of reusing the old cable if this is the case here.

[ac1951]

Thanks for the advice John... Looks like I better find my Micrometer unless you know of an easier way :-)

[TheScullster]

"John Rumm" wrote

When you say "wary of reusing" surely you aren't advocating ripping all the exsiting wiring out when all the OP seems to be interested in is separating the floors onto different circuits?

Phil

[Owain]

You could measure the resistance of the ring end-to-end and compare the L-L and N-N readings with the E-E. The relative resistances should be an indication of the relative conductor sizes, on the assumption that all other things are equal.

Owain

[John Rumm]

No, just take care. For example if not RCD protecting the circuits, then keep an eye on maximum earth fault loop impedance, disconnect times, and check the adequacy of the CPC in light of your prospective fault current (i.e. adiabatic equation). If RCD protecting the circuits then earth fault issues become less of a worry. Note also replacing an original rewireable fuse with a MCB would help since it removes the fusing factor from the sums.

(obviously "add some additional sockets" could mean anything 2 to 20 or more)