Smoke and heat detectors

[regsmyth]

I'm putting in two smoke alarms in the hall and a heat detector in the kitchen. Mains powered with battery backup.
http://www.tlc-direct.co.uk/Products/TLSD144.html
http://www.tlc-direct.co.uk/Products/TLSD146.html
I could put them either on the hall lighting circuit or I have space on the cu for them to be on their own circuit.
As far as I can tell, it's actually likely to be safer to put them onto the lighting circuit (via an FCU), since if there was a fault and the MCB tripped, I might not notice it. Ever.
Whereas if the lighting circuit tripped, I'd notice that evening when the lights wouldn't work.
But what if the fuse in the FCU blew?

Do they give out a visual and audible signal as soon as mains power is lost, or does the green led just go out? Cant tell from the info, perhaps someone will know.
And if say the fuse blew, does the battery immediately start getting heavier use? Or not?

Thanks for any thoughts.

 

[flameport]

As far as I can tell, it's actually likely to be safer to put them onto the lighting circuit (via an FCU), since if there was a fault and the MCB tripped, I might not notice it. Ever.

You would notice once the battery ran down, but that would be months later.

Whereas if the lighting circuit tripped, I'd notice that evening when the lights wouldn't work.
But what if the fuse in the FCU blew?

You don't need an FCU - connect directly to the lighting circuit.

Do they give out a visual and audible signal as soon as mains power is lost, or does the green led just go out?

On most (all?) of these alarms, the only indication of mains/no mains is the LED. They will beep when the battery needs replacing. The battery is only used when the mains is off, but even then the battery should still last for months. With mains power supplied, the battery won't need replacing for years.

 

[regsmyth]

Thanks that makes the case for coming off the lighting better, but I understand there has to be some form of accessible isolation for the circuit. Is the best thing to take a supply from a rose, down to a one way light switch? Or should it be a 6A DP switch?

And it could get turned off accidentally quite easily.

Perhaps best to take a second feed off the lighting mcb, to a labelled neon switch next to the cu, and then on to the first detector. Whadyareckon?

 

[ban-all-sheds]

What grade of system (as in BS 5839 categories) are you installing (or think you're installing ), and what are the RCD arrangements for the electrical installation?

 

[regsmyth]

It's a TT supply (thats the earth spike one isn't it?), with a split load cu, with the primary rcd jobbie a time delay one. The lighting and smoke systems will be on the time delay rcd side.
I hope I'm installing a safe grade of fire protection system, but can't quote BS category no.s I'm afraid.
If I'm doing anything horribly wrong I'll be a bit suprised, but I just wasn't sure of the best (most practical/economical/reliable/logical/common) arrangement for the supply and isolation of the system.
The alarms will be interlinked with standard 1.5mm 3c+e.
Do you think the labelled neon indicator switch for the isolation next to the cu provides the best solution?

 

[flameport]

I just wasn't sure of the best (most practical/economical/reliable/logical/common) arrangement for the supply and isolation of the system.

The usual method is to install a 6A MCB in the consumer unit, run 1mm twin and earth to the first/nearest detector, then 3core and earth from there to the next detector (with further 3c and earth to other detectors if you have them)

You don't need a switch, neon indicator, FCU or anything else. If they need to be turned off for replacement, cleaning or whatever else, the MCB is used.

As for the 3c and earth - use brown for live, grey with blue sleeve for neutral, and black with brown sleeve for the interconnect.

 

[regsmyth]

Flameport,
Thanks for that, the only problem is that if there was a fault, and the MCB tripped, how would I realise?
Hence probably safer to put it on the hall lighting circuit, then I'd know pretty quickly that there was a problem.
I had been thinking that the detectors themselves had to be isolatable (?) from the lighting circuit, but I guess not, so....
I think for me the best option is to take the feed to the first detector from the lighting mcb. No neons or other gubbins involved. And a spare way on the cu!
Thanks for the pointers.