I'm adding a couple of mains fed smoke alarms to my lighting circuit.
The first one is simple enough as there is a run of cable above the
location in the hallway. I'm intending to "loop in" the smoke alarm as
you would with a ceiling rose - allbeit without a switch

I'm not sure how to build the second alarm (upstairs) into the circuit.
Can I simply spur it off the downstairs smoke alarm using three+earth
(for the interconnect)? Or do I need to "loop in" the second alarm as
well? I've tried to illustrate both. I can't see why the first method
would be a problem, just wanted to check.

Spurred: ( = T&E, ||| 3&E Interconnect)

Rose ==== Smoke Alarm 1 ==== Rose
|||
|||
Smoke Alarm 2

Full Loop In: ( = T&E, =~= 3&E Interconnect)

Rose ==== Smoke Alarm 1 =~=~= Smoke Alarm 2 ==== Rose

"thankyousam" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed) oups.com...
> I'm adding a couple of mains fed smoke alarms to my lighting circuit.
> The first one is simple enough as there is a run of cable above the
> location in the hallway. I'm intending to "loop in" the smoke alarm as
> you would with a ceiling rose - allbeit without a switch
>
> I'm not sure how to build the second alarm (upstairs) into the circuit.
> Can I simply spur it off the downstairs smoke alarm using three+earth
> (for the interconnect)? Or do I need to "loop in" the second alarm as
> well? I've tried to illustrate both. I can't see why the first method
> would be a problem, just wanted to check.
>
> Spurred: ( = T&E, ||| 3&E Interconnect)
>
> Rose ==== Smoke Alarm 1 ==== Rose
> |||
> |||
> Smoke Alarm 2
>
> Full Loop In: ( = T&E, =~= 3&E Interconnect)
>
> Rose ==== Smoke Alarm 1 =~=~= Smoke Alarm 2 ==== Rose


You can just spur it off the first alarm.

"rrh" <(E-Mail Removed)> wrote in message
news:_IYdg.76606$(E-Mail Removed). uk...
>
> "thankyousam" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed) oups.com...
>> I'm adding a couple of mains fed smoke alarms to my lighting circuit.
>> The first one is simple enough as there is a run of cable above the
>> location in the hallway. I'm intending to "loop in" the smoke alarm as
>> you would with a ceiling rose - allbeit without a switch
>>
>> I'm not sure how to build the second alarm (upstairs) into the circuit.
>> Can I simply spur it off the downstairs smoke alarm using three+earth
>> (for the interconnect)? Or do I need to "loop in" the second alarm as
>> well? I've tried to illustrate both. I can't see why the first method
>> would be a problem, just wanted to check.
>>
>> Spurred: ( = T&E, ||| 3&E Interconnect)
>>
>> Rose ==== Smoke Alarm 1 ==== Rose
>> |||
>> |||
>> Smoke Alarm 2
>>
>> Full Loop In: ( = T&E, =~= 3&E Interconnect)
>>
>> Rose ==== Smoke Alarm 1 =~=~= Smoke Alarm 2 ==== Rose
>
>
> You can just spur it off the first alarm.

That's a bit dodgy innit? If your lighting is set up as one circuit to cover
the whole house, it may be OK but if the downstairs lights are on one fuse
and the upstairs lights a different fuse, someone could pull the fuse for
the upstairs and expect the smoke alarm to be safe to work on when it's not.

Steve.

I must admit that my instinct would always be to supply any sort of
alarm in a seperate manner to anything else. Disaster scenarios are
always "well thats's unlikely !" - but that's why you do a risk
analysis.

Let's say a fault develops in the lights circuit the OP is talking
about - it might generate adequate smoke for the alarm to sound before
the fuse blows, but what if it was the other way round - OK the fuse
has protected the system but the heat generated might by then have
ignited something else which will now not be detected by the alarm -
because it / has / no power !!

I woudl suggest if you can that you supply them both off a seperate
circuit from the CU.
And if you want to be really secure, you have a couple of battery ones
as well and exercise a bit of discipline in changing the batteries
regularly.
Rob

"Steve" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
> "rrh" <(E-Mail Removed)> wrote in message
> news:_IYdg.76606$(E-Mail Removed). uk...
>>
>> "thankyousam" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed) oups.com...
>>> I'm adding a couple of mains fed smoke alarms to my lighting circuit.
>>> The first one is simple enough as there is a run of cable above the
>>> location in the hallway. I'm intending to "loop in" the smoke alarm as
>>> you would with a ceiling rose - allbeit without a switch
>>>
>>> I'm not sure how to build the second alarm (upstairs) into the circuit.
>>> Can I simply spur it off the downstairs smoke alarm using three+earth
>>> (for the interconnect)? Or do I need to "loop in" the second alarm as
>>> well? I've tried to illustrate both. I can't see why the first method
>>> would be a problem, just wanted to check.
>>>
>>> Spurred: ( = T&E, ||| 3&E Interconnect)
>>>
>>> Rose ==== Smoke Alarm 1 ==== Rose
>>> |||
>>> |||
>>> Smoke Alarm 2
>>>
>>> Full Loop In: ( = T&E, =~= 3&E Interconnect)
>>>
>>> Rose ==== Smoke Alarm 1 =~=~= Smoke Alarm 2 ==== Rose
>>
>>
>> You can just spur it off the first alarm.
>
> That's a bit dodgy innit? If your lighting is set up as one circuit to
> cover the whole house, it may be OK but if the downstairs lights are on
> one fuse and the upstairs lights a different fuse, someone could pull the
> fuse for the upstairs and expect the smoke alarm to be safe to work on
> when it's not.
>
> Steve.
>

Can't lay my hands on the regs just now but they insist that interconnected
alarms are wired to one circuit only. Mains-powered alarms without battery
backup ("Grade E") should have their own dedicated (and preferably
non-RCD-protected) circuit from the consumer unit; mains-powered alarms with
battery backup ("Grade D") may be wired either that way or to a regularly
used local lighting circuit that is separately electrically protected.

On Sat, 27 May 2006 17:51:58 UTC, Owain <(E-Mail Removed)>
wrote:

> Ones that are supplied from a separate circuit don't have to have
> battery back-up; this, and the liklihood that loss of power on a
> separate circuit is less likely to be noticed, makes exclusively-powered
> alarms *less* reliable, IMHO.

I fitted battery-backed ones on a separate circuit, but included a very
visible (halfway up the stairs) non-maintained emergency light on the
same circuit (thus making it 'not exclusively powered', I'll admit..)

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
Avenue Supplies, http://avenuesupplies.co.uk

"Owain" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> robgraham wrote:
>> I must admit that my instinct would always be to supply any sort of
>> alarm in a seperate manner to anything else. Disaster scenarios are
>> always "well thats's unlikely !" - but that's why you do a risk
>> analysis.
>> Let's say a fault develops in the lights circuit the OP is talking
>> about - it might generate adequate smoke for the alarm to sound before
>> the fuse blows, but what if it was the other way round - OK the fuse
>> has protected the system but the heat generated might by then have
>> ignited something else which will now not be detected by the alarm -
>> because it / has / no power !!
>
> Smoke alarms which are supplied from lighting circuits have inbuilt
> battery or capacitor back-up power for several hours.

How long the batteries will last without ac power varies. Try 4 years not
several hours.eg.
<http://www.alertelectrical.com/product.asp?typeID=127&subID=250&prodID=2598&refId =4>

For what it is worth IMHO smoke alarms should be connected to the power for
the TV in most houses as any disruption in that supply would be noticed
first.

Adam

Christian McArdle wrote:
>> A centralised 'hush' switch is very useful if the installation is prone
>> to nuisance alarms.
>
> That is bad design. The alarm system should be designed not to have nuisance
> alarms, as they seriously damage the usefulness of the system. My system has
> gone off just once since it was installed 3 years ago. This was when the
> toaster set on fire. If my smoke alarm system went off, I would be
> immediately convinced that there was a fire. Compare with a poorly designed
> system with inappropriately chosen locations and sensor types that goes off
> every time someone has the full English and is completely ignored by
> residents.
>
> Christian.
>
>
Up till two days ago I would have said the same...4 a.m. Alarms go off.
I paddle round the house in the altogether prodding at each one. No sign
of smoke or fire. After about 5 minutes they stopped..weird..

Wasn't sure how to ID which one was the one that set the others a going..