lighting and smoke alarms on one circuit

[Guy]

Hi all,

Am doing a second fix and the sparky has the lighting circuit (loop) and the interconnected smoke alarms on the same circuit. The smoke alarms instructions state that it should be on a single circuit but I cant find anything in the regs to confirm wether this is exceptable practice or not. Comments on this would be appreciated.

 

[Zeespark]

Smokes can be run on their own circuit, or they can be run from a local, regularly used lighting circuit (with a switched spur at the front end). There is nothing much in BS7671 about this, this is more on the building regs side of things Guy.

AndyGuinness

 

[shed69]

I always wire my smokes on the same circuit as lights but what I do is have a rcbo and the circuit with just hallway and landing lights .....

---------- Post Auto-Merged at 17:45 ---------- Previous post was made at 17:43 ----------

Don't agree with them on they're own cos if you lose power and they don't beep then who knows they're not on but if your hallway and landing light doesn't work you sort it out straight away...

 

[Guy]

ok, ty for quick replies. I just phoned a friend and he added that in social housing the owners want the smokes on the lights to stop people switching the breaker off if the alarms start doing warning beeps! Thanks again

 

[SPECIAL LOCATION]

Regs would include:

134.1.1 Manufactures instructions..etc..

560.10 Fire detection systems shall co ply with BS5839.

As you say, domestic/ social / commercial etc..

can all have their own specific requirements..

:coffee

 

[SLIPSHOD & SLAPDASH]

But what about the manufacturer's instructions though ?

 

[Megaohm7]

There's nothing wrong with that and it was done like that so if the breaker did trip for some reason then no lights working would be more noticable instead of looking at a green led in the smoke alarm but with more twin RCD boards going in then you can have them on their own breaker as the RCD protecting those mcb's would probably trip first anyway knocking out a lighting circuit and maybe a socket circuit. However I would er on the side of caution and always follow the manufacturers instructions. It covers your backside too.

 

[SLIPSHOD & SLAPDASH]

Edit, single circuit means all detectors should be wired on the same circuit !

 

[Zeespark]

Megaohm, if the MCB knocks the circuit out, then the 9V battery in some smokes would kick in until the mains circuit is hopefully fixed.

AndyGuinness

 

[Megaohm7]

Megaohm, if the MCB knocks the circuit out, then the 9V battery in some smokes would kick in until the mains circuit is hopefully fixed.AndyGuinness

Yes that's true but you would want to know that the circuit is dead so you can do something about it. The battery is only a back up and mains should be restored asap.

 

[shed69]

Not supposed to put on side with sockets iirc which means neither side of db 90% of the time...

 

[NozSpark]

Not supposed to put on side with sockets iirc which means neither side of db 90% of the time...

Yep, they shouldn't share the same RCD as a socket circuit

 

[sparkytim]

Sorry to disagree but there is confusion about this due to the difference between BS 5839 Part 1 (NON domestic fire alarm systems with a Control Panel) and PART 6 (domestic systems)

DOMESTIC smoke alarm systems CAN share RCD with ANY CIRCUIT.

Restrictions ONLY apply to PART 1 NON domestic systems.

 

[NozSpark]

a) The normal supply for smoke alarms and any heat alarms in a Grade D system should be derived from the public electricity supply to the dwelling. The mains supply to the smoke alarms and heat alarms should take the form of either:

i) an independent circuit at the dwelling's main distribution board, in which case no other electrical equipment should be connected to this circuit (other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke alarms and any heat alarms) ; or

ii) a separately electrically protected, regularly used local lighting circuit.

What does this mean then? Particularly the bit in bold

 

[SPECIAL LOCATION]

Not supposed to put on side with sockets iirc which means neither side of db 90% of the time...

If thats true then 90% of others electrical design skills are stoopid IMHO!!

I can't see the logic of anyone installing any board with only 2xRCDs protecting everything...??? headbang

Either more RCBO's or high integrity Cu with some non RCD protected slots where you can put an RCBO if you want..

or have a non-RCD circuit...

We get loads of people moaning about the unreliability of RCD's and nuisance trips...

so I always make sure there is at least one (appropriately labeled) non-RCD socket and a separate slot for a smoke circuit if needed.

No worries about sharing with anything then. Guinness

 

[SLIPSHOD & SLAPDASH]

No comments on my earlier post ? The instructions say a' single circuit' This means all the interlinked devices are to be wired to one circuit, not seperate circuits such as up & downstairs ltg.

I raised the point regarding domestic smokes,RCD's & socket circuits being mixed with our assessor last visit. His reply was in a domestic situation a RCD tripped would be noticed so its ok to have smokes connected. I told him i did not agree as many people would not even know where or what the 'fusebox' was, let alone dare to reset a RCD so after a short while the batteries could go flat in the smokes. He replied if thats what i thought, fine. It also annoyed me, about 16 months or so ago the NICEIC in two different publications the same month ran articles contradicting this matter, I think the publications were Professional Electrician & the NICEIC news letter.

 

[Megaohm7]

I've got my assessment next Monday with Elecsa so I will raise it with him too.

 

[SPECIAL LOCATION]

Doesn't anyone else think there is a paranoia about the power going off on a Smoke Detector circuit???

Why would a mains powered battery back up alarm work for a severely less duration than a battery only operated alarm?

e.g.....

a battery only alarm will comfortably run for 12months or 18months+

So why would a mains operated one only run for a few hours when in battery standby mode? :|

Has anyone actually read any manufactures literature about how long their devices will run when the power is off???

We are not talking about emergency lights here with larger power consumption that only run for a few hours are we?

:C

 

[NozSpark]

Here's the reg

The capacity of the standby supply should be sufficient to power the smoke alarm(s) and any heat alarms in the quiescent mode for at least 72 h whilst giving an audible or visual warning of power supply failure, after which there should remain sufficient capacity to provide a fire warning for a further four minutes, in the absence of a fire, a fault warning for at least 24 h.