Smoke detectors - separate breaker

[Richard Russell]

In our (new build) house the three linked, mains (and battery) powered, smoke detectors were supposed to be fed from a separate breaker in the consumer unit. Except that they weren't - at some point during the build the connection was broken and the only practical way to restore operation was to wire them into the lighting circuit instead. The electricians assure me it's perfectly OK to do that, but what are the pros and cons of having a separate breaker for the smoke detectors?

Richard.

reply by email change 'news' to my forename.

[Lobster]

I don't think it's a big deal either way, given that there's battery backup.

Pro: If the breaker for the lighting circuit trips for some reason, it takes out the smoke detectors too

Con: If a separate breaker for the smoke detectors should trip, it could go unnoticed for months. ISTR someone on this group has this system with a battery-backed emergency light wired into the smoke-detector circuit, so if ever that light comes on during normal conditions, he knows it would mean the MCB has tripped - that strikes me as being the optimum solution.

David

[Andrew Gabriel]

IMO, it's much better to have the smoke detectors on a lighting circuit. You will notice quickly if they aren't working, and there's no temptation to trip them off to hush them, and then forget.

[Bob Eager]

[ARWadworth]

My suggestion to the council that smoke detectors should run (in their houses) "from the TV socket, as a power failure there would be noticed faster than any other power failure" fell on deaf ears.

As for the OPs question. A mains powered interlinked smoke alarm set up with a battery back up should last over a year without mains power and still function correctly. When the batteries start to lose power then warning bleeps are given out by the alarms to let you know. These warning bleeps will happen with or without mains power as it is the battery they test. Personally I prefer the smokes to be on the lighting circuit.

Adam

[Cod Roe]

I believe some interlinked smoke detectors (Kiddie made the one for which I was reading the manual) require all linked detectors to come off the same circuit, if you have them both upstairs and downstairs do you connect them to the upstairs or the downstairs lighting circuit? A separate breaker solves this problem.

[Bob Eager]

I have half a dozen Firex detectors, upstairs and downstairs. They are interlinked and need to be fed off a common power circuit. As previously noted, I use a separate MCB feeding them and a non-maintained emergency light on the stairs (which is both visible and usefully placed for a real power cut).

[Lobster]

Well for sure you must have all linked smoke detectors on the same circuit... but it's no more of a 'problem' than if you have separate upstairs and downstairs lighting circuits, with the landing light and hall light connected by two-way switching, which must be the situation in place in the majority of 2-storey homes.

David

[Jim Alexander]

I agree with what's been said about the advantages of connecting to a lighting circuit but read the regs and decide.

(para 1.19)

I note that if using a lighting circuit the alarms should be capable of being seperately isolated from the lighting circuit. Electrically I agree with that but can't help thinking it largely removes the advantage.

So for once you electricians are right, as long as they incorporate seperate isolation.

Jim A

[js.b1]

Personally I would do a hybrid.

- Upstairs lighting

- Downstairs lighting

- Smoke & Hall lighting

If the smoke alarm trips off, only the hall lighting goes with it.

The hall tends to be the one with incandescent light bulbs and more susceptible to B6 tripping. So when the hall trips off from a blown bulb all the rooms leading to it (up & down) still retain their lighting capability. Adding an EmLight to the hall circuit goes that useful bit further.

That meets the regs (314?) re minimised disruption from tripping.

Having an isolator to smoke alarms supplied by a lighting circuit is useful so the alarms can be isolated when doing Ins Test part of PIR. Which reminds me to add one at some point.

-- J.SB.

[Andy Hall]

One flaw in this. In looking at the instructions for several alarm types, if interconnect is used, they must be on the same circuit.

[David Hansen]

On Sun, 30 Mar 2008 13:30:35 +0100 someone who may be Andy Hall wrote this:-

Generally smoke alarms are fitted in the landings at stairs. Generally the stair lights are on one circuit.

Adding smoke alarms to every room is possible, but whether it is worthwhile is debatable.

[Owain]

Sounders in every bedroom may be required to get adequate sound level at the bedhead. That is rarely the best location for sensors.

Owain