smoke detectors

[abertawejack]

Hi Guys
I'm rewiring my property and not sure whether the smoke detectors should be wired to a regularly used lighting circuit or wired to a dedicated circuit via an rccb.
also in the cloakroom I have placed a fcu in the room to supply a macarator, is this an accepted practise as there is no shower in this room.
regards
abertawejack

 

[wingcoax]

Defo use lighting circuit for smokes, if the FCU is not anywhere near the water you may be alright.

 

[Chri5]

Smoke detection feed is a preference subject- Some will take the thought that hanging the units off a frequently used lighting circuit gives a clear fail signal to the dweller if the rcd trips and thus the units have no power.

I go with a dedicated rcbo 6 amp circuit and smoke units that will alarm when the battery runs down if the rcbo trips and the power stops.

My feeling is that running the smokes via an rcd rail with shared circuits gives the prospect of the units failing due to a multitude of possibilities added to by the other circuits.


As for the cloak room you need to check the position of the f/spur against the 17th zone diagram for bathrooms / wet areas (see on site wiki).

 

[PrinceofDarkness]

An FCU is fine in a cloakroom. It doesn't matter that there's a water supply there. The thing that matters is whether there's a bath tub or shower tray, whereby the user would have bare-footed contact with 'wet earth'. This isn't the case here, as you're already said.

Smoke alarms: In recent years it has become the preference of nearly all Local Authorities in England and Wales for such devices to be connected to a principal lighting circuit - this is supported by the Fire & Rescue Service- and for good reason:

When the old-fashioned battery-only detectors had a low battery they would emit an annoying 'bleep' which used to cause certain householders to remove the battery with the 'intention' to replace the battery 'in due course'. The same is true for mains/battery detectors on a 'dedicated circuit', because the same twit of a user is enabled to remove the battery and also switch off the dedicated MCB.

It's a different matter if that user has to switch off his lights as well.

Now and then a lighting/smoke detector circuit might trip its MCB - that's when the battery back-up comes in handy.........




Lucia.

 

[riveralt]

Smoke alarms: In recent years it has become the preference of nearly all Local Authorities in England and Wales for such devices to be connected to a principal lighting circuit - this is supported by the Fire & Rescue Service- and for good reason:

When the old-fashioned battery-only detectors had a low battery they would emit an annoying 'bleep' which used to cause certain householders to remove the battery with the 'intention' to replace the battery 'in due course'. The same is true for mains/battery detectors on a 'dedicated circuit', because the same twit of a user is enabled to remove the battery and also switch off the dedicated MCB.


Lucia.

I agree with you, but the problem is that if you run the smoke alarm circuit through a main lighting circuit you have to provide a means of isolating the supply to the alarms without switching off the lighting.

So when the battery starts beeping, the same twits will still have the ability to switch of the smoke alarms with no affect on the lighting.

On that basis it doesn't really matter how you connect the smoke alarms - dedicated or piggy backed circuits - its down to the individual homeowner to ensure that the alarm circuit/alarms are properly maintained.

 

[PrinceofDarkness]

I don't follow your reasoning there, Riveralt. You're the only person that I've noticed, who has mentioned a separate means of isolation for SD's.

Why would a group of SD's need separate isolation, other than the circuit MCB?



Lucia

 

[mikhailfaradayski]

IIRC, if its a grade D smoke alarm, then it can be supplied from lighting circuit or its own mcb/rcd. If its grade E, then it must be fed from its own dedicated mcb/rcd.

Not that it makes much sense, but i do think that if you have them from a lighting circuit, then isolation (via fcu) should be provided.

 

[holmslaw]

..

 

[riveralt]

I don't follow your reasoning there, Riveralt. You're the only person that I've noticed, who has mentioned a separate means of isolation for SD's.

Why would a group of SD's need separate isolation, other than the circuit MCB?

Lucia

Approved Document Part B Section B1 (1.19)

"The power supply for a smoke alarm system should be derived from the dwellinghouse's main electricity supply. The mains supply to the smoke alarm(s) should comprise a single independent circuit at the dwellinghouse's main distribution board (consumer unit) or a single regularly used local lighting circuit. This has the advantage that he circuit is unlikely to be disconnected for any prolonged period. There should be a means of isolating power to the smoke alarms without isolating the lighting."

I accept that this document is classed 'for guidance' and you can, of course, achieve the same result by other means.

I also accept your point about Local Authorities et al preferring to have such devices connected to a principal lighting circuit, but that preference must have been based on something. I would suggest it was based on this approved document. If that is the case then the full content of that paragraph should be taken into account.

In the design of my installations, whenever possible, I put the smoke detector circuit on its own circuit.

 

[1john]

you could fit a key switch for isolation from the lighting circuit.

 

[Spark123]

I believe it is considered bad practice to install smokes on the same RCD as socket outlets, the best way imo is going to be putting them on their own RCBO.

 

[wingcoax]

I have a full smoke/fire system installed with it's own dedicated supply and a secret keyswitch fcu. This was installed that way as my premises are partly commercial, before i bought it. Personally as i said i always install from lighting circuits.

 

[GaryMo]

I believe it is considered bad practice to install smokes on the same RCD as socket outlets, the best way imo is going to be putting them on their own RCBO.

Correct for a Grade E system but nothing mentioned regarding sharing a common RCD with socket outlet circuits for a more commonly used Grade D system in BS 5839-6:2004.

Grade E

c) The circuit serving the smoke alarm(s) and any heat alarms should preferably not be protected by any
residual current device (r.c.d.). If r.c.d. protection is required for reasons of electrical safety
(e.g. in an installation forming part of a TT system), either of the following conditions should be satisfied.
i) The r.c.d. should serve only the circuit supplying the smoke alarm(s) and heat alarms.
ii) The r.c.d. protection of a smoke alarm circuit should operate independently of any r.c.d. protection
for circuits supplying socket outlets or portable equipment.

 

[PrinceofDarkness]

Hello Riveralt, that gradual change of LA thinking came about not through the Approved Document recommendations, but through the concerns raised by The Fire and Rescue Service when they launched their 'Smoke Detector Awareness campaign ' during 2007.

The main concern was to find a way to prevent unthinking householders to easily disable their alarms.

I've no doubt that most householders, tenants etc - when they remove a battery and disconnect the suppy - have the intention of buying a new battery 'eventually', but 'eventually' sometimes comes too late........

Lucia.

 

[LoveRocket]

Absolutely 100% from a lighting circuit - with NO means of isolation other than the lighting MCB/RCBO. Common sense says that isolation is only required if there's no other source of light in the area of the smokes, ie in a room with no windows. In a house this is nearly impossible, so there's no need to have an isolation switch between your lighting circuit and the smokes