Reusing old shower circuit to supply bathroom electrics?

[Thrashman]

Reusing old shower circuit to supply bathroom electrics?
Hi everyone, hope you’re all doing well.
So this is potential plan,

Working on the property and there is a consumer unit with all RCBO’s,
But the entire lighting for the three bedroomed house is on one RCBO.
Going to be installing new spotlights (downlights), LED mirror and new extractor fan to bathroom. Ideal situation to give segregation of circuits would be to have the bathroom on its own circuit, so they’re not plunged into darkness if there is a fault anywhere in the house.

The consumer unit is a Siemens and have scoured absolutely everywhere and unable to find a 6amp RCBO for these for a new circuit .
So...
The shower circuit is now redundant, so considering using this to supply the bathroom.

Currently a 6mm cable on 32A
Type A Rcbo, Would bring the end of the 6mm cable down into a SFCU, And fuse down at 3 A ( So then cover my extractor fan as per manufacturers instructions) continue all my other wiring from there . Technically the 6mm cable is protected by the 32 amp RCBO and my 1.5 mil cable will be protected by the 3amp at the SFCU, So this all seems feasible and gives me segregation for the lighting.
I know in an ideal situation a new circuit would be run in 1.5, but as I’m unable to source a suitable RCBO this seems like the best alternative rather than putting all the bathroom lighting on the same lighting circuit.
I would label the board up accordingly,
Just to confirm the 6mm supply has tested out fine .

Opinions, thoughts and agreements and disagreements please,

thanks in advance

 

[westward10]

I don't see the point, the current set-up is what it is. Separating the bathroom onto its own circuit isn't going to be of huge benefit should the existing lighting circuit fail.

 

[Dartlec]

Electrical safety wise, I don't see a major issue with this as a plan and can't immediately see how it would not comply, even if it is a bit of a 'hack' and would never be installed from new. It's not noticeably different from taking a fused spur off a socket circuit, which happens frequently for retro-fit lighting circuits where no suitable circuit is nearby.

Marking everything up and documenting it for the next guy who will have to EICR it is of course a very good idea. The SFCU should also be accessible in my view, rather than buried in the loft with no markings.

Whether it's necessary or not may be a judgement call. Obviously having all the lights on one RCBO isn't great. Does the RCBO trip often though? You may be overthinking it if the light fittings are the sort that haven't tripped anything for months/years and it's a newer build.

Only thing that springs to mind is that you may struggle to get 6mm cable well terminated into some SFCU terminals and it may well need at least a 32mm back box

 

[Strima]

Personally I would probably spur of another circuit such as sockets leaving the shower circuit for future use.

A 6mm cable may well come in handy in a few years time if they decide to revert back to an electric shower or add PV etc.

 

[pc1966]

As westward10 said, it seems a bit unnecessary.

If there are other concerns about safety should the lights fail (e.g. infirm occupant, stairs, etc) then a better solution might be to have some emergency lighting covering that area. Would also cover other power outages and not just a RCBO trip.