Can mains Smoke/Heat alarms share same circuit as an Intruder alarm? (Building Regs/BS7671)

[eveares]

Can mains Smoke/Heat alarms share the same electrical circuit in the domestic distribution board/consumer unit as an Intruder alarm under building regs/BS7671/ what ever regulation covers mains smoke alarms?

Just seems wasteful to waste two ways in a electrical distribution board, not to mention you are more likley to notice a power failure of an intruder alarm than a mains smoke alarm, which if combined on the same circuit, would get more quickly noticed imo.

Regards: Elliott.

 

[Murdochcat]

I never put smoke alarms on their own circuit. Best on a lighting circuit so the breaker won’t turn be turned off

There is no regulation about this BUT there used to be a myth about smokes being on a dedicated circuit - which IIRC came from the NICEIC

 

[Deryck Tintagel]

I can't say as I do not know but an interesting question. I have smoke alarms on a dedicated MCB but I took the supply to the intruder alarm from the lighting circuit on the first floor. I have been pondering moving the supply to the smoke alarm circuit as my alarm beeps every minute when the mains is off and it is annoying if working on the lighting. It would be useful in the event the smoke circuit ever tripped.

 

[EFLImpudence]

Can mains Smoke/Heat alarms share the same electrical circuit in the domestic distribution board/consumer unit as an Intruder alarm

Yes, why should they not?

 

[eveares]

Yes, why should they not?

So why in new builds, are they often put on their own circuit and it's recommended to do it this way?

 

[EFLImpudence]

So why in new builds, are they often put on their own circuit and it's recommended to do it this way?

I don't know.

 

[Murdochcat]

So why in new builds, are they often put on their own circuit and it's recommended to do it this way?

Probably because somebody with little or no knowledge of the regulations are working on new builds and making poor decisions

 

[Risteard]

Yes, why should they not?

BS 5839-6 mentions either a dedicated circuit with no other electrical equipment connected, or a regularly used local lighting circuit.

 

[JohnW2]

BS 5839-6 mentions either a dedicated circuit with no other electrical equipment connected, or a regularly used local lighting circuit.

As I,and others, often say, the latter makes sense, but I'm far less sure about the former. The only saving graces are (a) that the alarms willhave back-up batteries and (b) that at least some of them will alert the householder to a mains failure

 

[Taylortwocities]

my alarm beeps every minute when the mains is off

That is the alarm telling you that the power is off. A correct and proper thing for it to do!

 

[Risteard]

That is the alarm telling you that the power is off. A correct and proper thing for it to do!

May be the low battery warning.

 

[eveares]

May be the low battery warning.

That may be it as I have never known smoke alarms to beep only when the mains power is off.

 

[Risteard]

As I,and others, often say, the latter makes sense, but I'm far less sure about the former. The only saving graces are (a) that the alarms willhave back-up batteries and (b) that at least some of them will alert the householder to a mains failure

Incidentally I've checked the current version of BS 5839-6 and the wording appears to have changed slightly to "a separately protected, regularly used local circuit..." so it does not now specifically stipulate a "regularly used local lighting circuit". (Source: BS 5839-6:2019+A1:2020.)

 

[Murdochcat]

That may be it as I have never known smoke alarms to beep only when the mains power is off.

They might do that if the battery needs replacing