Smoke Alarms

[ac1951]

Going to be installing two inter-linked mains powered Smoke Alarms Two questions: Q1..Any recomendations on make and model Q2..Should I connect them on a separate cct or should I connect to Lighting cct

[stevelup]

The Kidde ones are good and there is a complete range including heat detectors and carbon monoxide detectors - all of which are interlinkable.

Logic suggests they would be best on their own circuit but I don't know what the regs are.

Steve

[Lobster]

Not necessarily - if they were on their own circuit, and that circuit failed and/or the MCB tripped, you might never know until there's a fire and it doesn't work. OK, there should be battery back-up, but you could basically convert your mains-powered alarm into a battery one, without even realising... and being nominally a mains-powered one, you might be forgiven for being less rigourous about changing the battery as often as you otherwise would.

Whereas if the smoke alarm's on the lighting circuit, and that fails, you'll know PDQ.

David

[John Rumm]

You might notice the power light on the alarms has gone out though ;-)

Building regs document B1 has a fair bit of useful stuff on this, and it is a slight catch22 situation - you can't have it/them on non dedicated circuit unless they have a backup power source:

"Power supplies

1.17 The power supply for a smoke alarm system should be derived from the dwelling's mains electricity supply. The mains supply to the smoke alarm(s) should comprise a single independent circuit at the dwellings main distribution board (consumer unit). If the smoke alarm installation does not include a stand-by power supply, no other electrical equipment should be connected to this circuit (apart from a dedicated monitoring device installed to indicate failure of the mains supply to the smoke alarms - see below).

1.18 A smoke alarm, or smoke alarm system, that includes a standby power supply or supplies, can operate during mains failure. It can therefore be connected to a regularly-used local lighting circuit. This has the advantage that the circuit is unlikely to be disconnected for any prolonged period.

1.19 Devices for monitoring the mains supply to the smoke alarm system may comprise audible or visible signals on each unit or on a dedicated mains monitor connected to the smoke alarm circuit. The circuit design of any mains failure monitor should avoid any significant reduction in the reliability of the supply, and should be sited so that the warning of failure is readily apparent to the occupants. If a continuous audible warning is given, it should be possible to silence it.

1.20 The smoke alarm circuit should preferably not be protected by any residual current device (rcd). However if electrical safety requires the use of a rcd, either:

a. the smoke alarm circuit should be protected by a single rcd which serves no other circuit; or

b. the rcd protection of a smoke alarm circuit should operate independently of any red protection for circuits supplying socket-outlets or portable equipment."

[Bob Eager]

I used Firex ones because they were easily obtainable and they can be fitted easily to a quick release pattress. And they come in all the types I needed (optical, ionisation and heat rise).

I used a separate circuit, but you need to know if that circuit has tripped. I fixed that, and got a bonus, by wiring in a non-maintained emergency light (i.e. one that lights only on power failure, via battery and inverter) and placing that in a prominent position on the starirs. The bonus is that if all power fails at night, there's less chance of breaking your neck.

[Gel]

SOURCE HERE:

on wiring in Installer manual from here:

Go to downloads, manuals section.

[Lobster]

The mains-powered ones I fitted not long ago don't have one of those...

ie, a battery? Which can go flat and would render the alarm useless if not checked? - That's the scenario I painted above.

David

[John Rumm]

Possibly not. All the recent ones I have seen have one though.

Indeed. I was just highlighting that if you want to share a lighting circuit for the reasons you outlined, then you must use the alarms with a battery (since there is more likelihood the circuit will be de energised as a result of an external influence (bulb blowing tripping the MCB etc).

If you use alarms without a battery, then they need their own circuit.

[ac1951]

Lots of useful information .. many thanks.

Not much on recommended models though ? Reason for asking is: Good cable connectivitity (not some scrappy terminals that need a jewelers screw driver and a magnifing glass to access) Plastic covers that break if you open them more than a couple of times. Battery holders that snap when you try to change the battery (not that I'm expecting to change this on a re-chargeable one) and then there's the batteries (Lithium, or something else) which one do you choose and why? I heard that some have a "sleep mode" you can activate whilst you're cooking dinner. Are these any good ?

Andy

[Bob Eager]

The Firex ones have a separate pattress. You connect the feed cables via a built in choc block. Plenty of capacity. The alarm itself has a flying lead with a plug that connects to the pattress. The alarm rotates and clicks into place on the pattress.

No actual plastic cover; simply remove from pattress and battery cover is on the back.

They use a non-rechargeable battery.

No need. Use the correct detector, which won't give a false alarm (weorks on heat rise rate rather than smoke).

[Jim Alexander]

Installed Ei140 series several years ago.

't recall any installations problems. Installed on a dedicated circuit without power failure detection. If I fail to notice the green led is not on then backup battery operates it until it beeps on a depleted battery according to the instructions. They have worked on the few occasions tested.

Jim A

[Andrew May]

I used the Kidde ones from TLC. No problems yet.

Fire alarms seem to be one of those instances where the ODPM has shot itself in the foot with Part P. Installing on a dedicated circuit is preferable but require building control notification and inspection if you are doing it yourself. Adding to an existing lighting circuit does not. You could get an further four alarms with whatever additional protection that that may provide for the price of the notification/inspection.

Andrew