Dual use building -smoke alarms fed from a different supply?

[baggy99]

OK, here's the scenario. 3 storey property - commercial on the ground floor, 2 floor maisonette above. The maisonette has it's own supply, meter, CU, etc, located inside the property, BUT the smoke alarms (proper battery/mains interlinked jobs) are fed from the CU in the commercial property.
Is this OK? I can't see any way around it, but you could argue a scenario where the householder switches off the incoming mains but still has a live circuit in his property fed from elsewhere.
This must be a common issue in multi-occupancy buildings - what's the recommended treatment? Is is sufficient to label the CU to inform the user that the smoke alarm circuit remains live regardless of the incomer being switched off?
Thanks.

 

[Chri5]

It's not similar to MOH- which is 1 x dwelling, 1 x CU and multiple occupants that would all have access to the CU.

Yours is 2 x premises and unless the occupier of the maisonette has access to the grd floor premises to isolate then I'd discon the upper smokes and recon to the correct CU.

Think about it, does the grd floor smoke need to alarm what is a different premises when it alarms and ditto does the maisonette need to alarm the grd floor.

No !

Otherwise why would flats have there 'own' rather than shared smoke detection.

As for difficult, how hard can it be to discon the link between grd and 1st smoke in the maisonette and then provide power, via an adjacent light for the maisonette ?

 

[baggy99]

Cheers Chri5. I see your logic and it looks like I'll have to reconfigure as you suggest.
The building will be due a final inspection by the BCO, so my next question is......
Is it OK to feed the maisonette alarms off a lighting circuit (ie not off their own dedicated MCB/RCBO?)
The lighting circuits are currently split across the 2 floors. Each circuit is fed from it's own 6A RCBO (per 17th ed.) It would be easiest to take the feed from the upstairs circuit as I can access both the alarm & the lighting circuits from the loft. The upstairs lighting circuit currently has 7 fittings hanging off it, max 100W ea.
I realise that in an ideal world the alarms should have their own RCBO, but is it ACCEPTABLE UNDER THE REGS to hang the smokes off a lighting circuit? BTW, this is an extensive refurb project, not a new build.
Thanks.

 

[Chri5]

Yes it is acceptable to run smokes via lighting circuit.

Since the smokes may be prone to fuse pops on the lighting circuit, use ones with decent battery backup.

Ideally the smokes would be on the direct rail of a 17th CU with 6a dedicated RCBO, but the backup batteries give some protection and smoke use, should the light circuit fail.

 

[baggy99]

Thanks again