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" wrote in message
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" wrote in message
. uk...

"thankyousam" wrote in message
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" wrote in message
...

"rrh" wrote in message
. uk...

"thankyousam" wrote in message
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
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

In message , Owain
writes

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


Just a thought, I have mains powered, battery backed up, smoke detectors
in most rooms of the house and they are fed from one supply and also
inter linked so that if one goes then they all sound, plus an isolating
switch so that it is possible to turn off all bar the one that
activated. The other thing I have done is to fit some emergency light
units to the same circuit, this has the advantage of indicating if the
circuit has tripped for any reason.
--
Bill

"Owain" wrote in message
...
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

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.

They shouldn't expect any such thing, as to connect them up in that manner
would be against the regulations, which requires all smoke alarms to be
interconnected and on the same circuit (either a regularly used lighting
circuit, or a dedicated alarm circuit).

If they are expecting smoke alarms to be distributed across multiple alarm
circuits, then they aren't competent to work on an electrical installation.
They are also not competent to work on electrical installations if they
think that flicking an SP MCB is enough to consider a circuit to be
deenergised, let alone isolated.

Christian.

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.

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..

On Tue, 30 May 2006 17:18:06 +0100, "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.

I agree that Nuisance alarms seriously damage their usefulness.
However I have never managed to find alarms that do not have false
alarms. About a year ago we had some mains smoke alarms
professionally fitted (I have checked they have been fitted correctly)
and they still go off occasionally when we cook or when I do some DIY.

The false alarms have gradually increased in frequency since they were
fitted. And we do vacuum them out regularly.

Mark

About a year ago we had some mains smoke alarms professionally
fitted (I have checked they have been fitted correctly) and
they still go off occasionally when we cook or when I do some
DIY.

What type of alarms are on the same floor as the kitchen
(ionisation/optical/thermal) and where are they installed?

Christian.

On Wed, 31 May 2006 16:03:45 +0100, "Christian McArdle"
wrote:

About a year ago we had some mains smoke alarms professionally
fitted (I have checked they have been fitted correctly) and
they still go off occasionally when we cook or when I do some
DIY.

What type of alarms are on the same floor as the kitchen
(ionisation/optical/thermal) and where are they installed?

I'll need to check on the type. There is one installed on the ground
floor in a hallway near the bottom of the stairs. It's about 2m from
the Kitchen door.

Mark.

I'll need to check on the type. There is one installed on the ground
floor in a hallway near the bottom of the stairs. It's about 2m from
the Kitchen door.

Do all rooms on the ground floor lead from the hall? What rooms are there?
How large is the hall?

Christian.

On Thu, 1 Jun 2006 09:40:10 +0100, "Christian McArdle"
wrote:

I'll need to check on the type. There is one installed on the ground
floor in a hallway near the bottom of the stairs. It's about 2m from
the Kitchen door.

Do all rooms on the ground floor lead from the hall? What rooms are there?
How large is the hall?

On the ground floor the Lounge and Kitchen lead off the hall. The
Hall is about 3m x 2m approx.

Mark

Do all rooms on the ground floor lead from the hall? What rooms are
there?
How large is the hall?

On the ground floor the Lounge and Kitchen lead off the hall. The
Hall is about 3m x 2m approx.

Some possible solutions:

1. Replace existing hall ionisation alarm with optical type and move away
from kitchen door, if at all possible. An optical alarm is less likely to be
set off by a few cooking fumes.

2. Remove hall alarm. Install heat sensed alarm in kitchen. Install
ionisation alarm in lounge.

The second solution probably doesn't quite match building regulations as
there would be no detector in the downstairs circulation space. However, in
my opinion it would be safer, as it would reduce false alarms, which are
dangerous, whilst still maintaining detection in all rooms likely to have
fires. A fire in the hall itself is unlikely and will set off your upstairs
detector in any case.

Christian.

On Mon, 5 Jun 2006 10:28:07 +0100, "Christian McArdle"
wrote:

Do all rooms on the ground floor lead from the hall? What rooms are
there?
How large is the hall?

On the ground floor the Lounge and Kitchen lead off the hall. The
Hall is about 3m x 2m approx.

Some possible solutions:

1. Replace existing hall ionisation alarm with optical type and move away
from kitchen door, if at all possible. An optical alarm is less likely to be
set off by a few cooking fumes.

Thanks. I might try this.

2. Remove hall alarm. Install heat sensed alarm in kitchen. Install
ionisation alarm in lounge.

Regards,
Mark