mains smoke alarms

[magico]

been a while since i was starting this job,so just checking i have this right.
i`m installing 3 mains smoke alarms,1 on each floor.they are battery back up so i`m running them of loft landing 2 way light.
so do i use 2 core and earth from ceiling rose to no 1 smoke alam then 3 core and earth to the other 2?
cheers
mark

 

[starspark]

got it in one!!
live neutral earth from pendant to first smoke alarm then 3core between 1st to 2nd and 2nd to third live neutral interconnection.

 

[RF Lighting]

They should idealy, if at all possible be on their own dedicated circuit.

 

[fireman22]

rf not according to bs 5839 part 6, they say if it is on a lighting circuit if circuit trips it will be noticed earlier and more than likely be reinstated.

 

[RF Lighting]

I'm not disputing BS5839 but if they are wired of the lighting they are far more likely to lose power, than if they were on their own circuit. Also the detectors with battery backup will beep intermittently to warn you of mains failure.

 

[fireman22]

all down to worst case senario, you go out circuit trips batts all low beep for a while then die completly you come home none the wiser go to bed no protction. put them on lighting circuit safer and correct

 

[plugwash]

i seem to remember that if they are mains only they have to be on a dedicated circuit. If battery backed up then they can be either on a dedicated circuit or a "local lighting circuit"

the problem with using the lighting cuircuit is that most houses have more than one and i don't belive its reccomended to interlink alarms on different circuits. So whichever lighting circuit you put them on it won't be a local one in all parts of the house.

 

[fireman22]

why would you be interlinking them off different circuits? if you were going to interlink them you would normally use 3 core and earth cable and feed mains on three of the cores and interlink connection would be on the fourth core.

 

[plugwash]

EXACTLY

so whatever circuit you power them from it won't be a "local lighting cuircuit" from the perspective of all the smoke alarms.

 

[fireman22]

smoke alarms don't need to be on a local lighting circuit to their vicinity