Mains Smoke Alarms

The hardwired ones can still share a circuit, although the tap from the existing circuit can obviously only be at a single point, then dedicated cabling to the other alarms.

Right, so if you tap in say down stairs, do you have to run dedicated cabling to the upstairs from that one as well?

Yes you still need dedicated cabling. Well I suppose in theory to could tap power in multiple places (from the same lighting circuit), but you'd still need to run a (sheathed) single between floors to provide the signalling, so you might as well run power too, and avoid confusing future electricians.

Ok, that make sense

Do you typically use a 3 core T&E, or standard 2 core and use the earth for signal?
Or a completely different core colour set all together?

3 core + earth MUST BE USED; just download an installer's manual from any alarm manufacturer's website.

Much appreciated, thanks

RustyH said:

Do you typically use a 3 core T&E, or standard 2 core and use the earth for signal?

As said above, you need 3 core & E so that you have the signal between alarms so that they all go off together. Even if the alarms require no earth, you should not use the circuit protective conductor in T & E and absolutely not in a flex or other type of cable in which the cpc's insulation is green and yellow.

My personal preference is hard-wired over wireless, and installation on its own circuit on an RCBO. Even with battery back up, you don't really want an RCD trip due to another circuit to disconnect your fire alarm system.

My personal preference is to share the circuit, on the grounds that if the lights trip, someone will get it fixed quickly. Conversely, the alarm RCBO, once tripped, may remain tripped for years.

WW, I completely agree with that alternative approach - it's equally valid.