Smoke Alarms


A

ac1951

Going to be installing two inter-linked mains powered Smoke Alarms
Two questions:
Q1..Any recomendations on make and model
Q2..Should I connect them on a separate cct or should I connect to
Lighting cct
 
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S

stevelup

Going to be installing two inter-linked mains powered Smoke Alarms
Two questions:
Q1..Any recomendations on make and model
Q2..Should I connect them on a separate cct or should I connect to
Lighting cct
Hi

The Kidde ones are good and there is a complete range including heat
detectors and carbon monoxide detectors - all of which are
interlinkable.

Logic suggests they would be best on their own circuit but I don't
know what the regs are.

Steve
 
L

Lobster

stevelup said:
Logic suggests they would be best on their own circuit but I don't
know what the regs are.
Not necessarily - if they were on their own circuit, and that circuit
failed and/or the MCB tripped, you might never know until there's a fire
and it doesn't work. OK, there should be battery back-up, but you could
basically convert your mains-powered alarm into a battery one, without
even realising... and being nominally a mains-powered one, you might be
forgiven for being less rigourous about changing the battery as often as
you otherwise would.

Whereas if the smoke alarm's on the lighting circuit, and that fails,
you'll know PDQ.

David
 
J

John Rumm

Lobster said:
Not necessarily - if they were on their own circuit, and that circuit
failed and/or the MCB tripped, you might never know until there's a fire
and it doesn't work. OK, there should be battery back-up, but you could
You might notice the power light on the alarms has gone out though ;-)
basically convert your mains-powered alarm into a battery one, without
even realising... and being nominally a mains-powered one, you might be
forgiven for being less rigourous about changing the battery as often as
you otherwise would.

Whereas if the smoke alarm's on the lighting circuit, and that fails,
you'll know PDQ.
Building regs document B1 has a fair bit of useful stuff on this, and it
is a slight catch22 situation - you can't have it/them on non dedicated
circuit unless they have a backup power source:

"Power supplies
1.17 The power supply for a smoke alarm system should be derived from
the dwelling's mains electricity supply. The mains supply to the smoke
alarm(s) should comprise a single independent circuit at the dwellings
main distribution board (consumer unit). If the smoke alarm installation
does not include a stand-by power supply, no other electrical equipment
should be connected to this circuit (apart from a dedicated monitoring
device installed to indicate failure of the mains supply to the smoke
alarms - see below).

1.18 A smoke alarm, or smoke alarm system, that includes a standby
power supply or supplies, can operate during mains failure. It can
therefore be connected to a regularly-used local lighting circuit. This
has the advantage that the circuit is unlikely to be disconnected for
any prolonged period.

1.19 Devices for monitoring the mains supply to the smoke alarm system
may comprise audible or visible signals on each unit or on a dedicated
mains monitor connected to the smoke alarm circuit. The circuit design
of any mains failure monitor should avoid any significant reduction in
the reliability of the supply, and should be sited so that the warning
of failure is readily apparent to the occupants. If a continuous audible
warning is given, it should be possible to silence it.

1.20 The smoke alarm circuit should preferably not be protected by any
residual current device (rcd). However if electrical safety requires the
use of a rcd, either:

a. the smoke alarm circuit should be protected by a single rcd which
serves no other circuit; or

b. the rcd protection of a smoke alarm circuit should operate
independently of any red protection for circuits supplying
socket-outlets or portable equipment."
 
B

Bob Eager

Going to be installing two inter-linked mains powered Smoke Alarms
Two questions:
Q1..Any recomendations on make and model
I used Firex ones because they were easily obtainable and they can be
fitted easily to a quick release pattress. And they come in all the
types I needed (optical, ionisation and heat rise).
Q2..Should I connect them on a separate cct or should I connect to
Lighting cct
I used a separate circuit, but you need to know if that circuit has
tripped. I fixed that, and got a bonus, by wiring in a non-maintained
emergency light (i.e. one that lights only on power failure, via battery
and inverter) and placing that in a prominent position on the starirs.
The bonus is that if all power fails at night, there's less chance of
breaking your neck.
 
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L

Lobster

John said:
You might notice the power light on the alarms has gone out though ;-)
The mains-powered ones I fitted not long ago don't have one of those...
Building regs document B1 has a fair bit of useful stuff on this, and it
is a slight catch22 situation - you can't have it/them on non dedicated
circuit unless they have a backup power source:
ie, a battery? Which can go flat and would render the alarm useless if
not checked? - That's the scenario I painted above.

David
 
J

John Rumm

Lobster said:
The mains-powered ones I fitted not long ago don't have one of those...
Possibly not. All the recent ones I have seen have one though.
ie, a battery? Which can go flat and would render the alarm useless if
not checked? - That's the scenario I painted above.
Indeed. I was just highlighting that if you want to share a lighting
circuit for the reasons you outlined, then you must use the alarms with
a battery (since there is more likelihood the circuit will be de
energised as a result of an external influence (bulb blowing tripping
the MCB etc).

If you use alarms without a battery, then they need their own circuit.
 
A

ac1951

Lots of useful information ..
many thanks.

Not much on recommended models though ?
Reason for asking is:
Good cable connectivitity (not some scrappy terminals that need a
jewelers screw driver and a magnifing glass to access)
Plastic covers that break if you open them more than a couple of
times.
Battery holders that snap when you try to change the battery (not that
I'm expecting to change this on a re-chargeable one)
and then there's the batteries (Lithium, or something else) which one
do you choose and why?
I heard that some have a "sleep mode" you can activate whilst you're
cooking dinner. Are these any good ?

Andy
 
B

Bob Eager

Lots of useful information ..
many thanks.

Not much on recommended models though ?
Reason for asking is:
Good cable connectivitity (not some scrappy terminals that need a
jewelers screw driver and a magnifing glass to access)
The Firex ones have a separate pattress. You connect the feed cables via
a built in choc block. Plenty of capacity. The alarm itself has a flying
lead with a plug that connects to the pattress. The alarm rotates and
clicks into place on the pattress.
Plastic covers that break if you open them more than a couple of
times.
No actual plastic cover; simply remove from pattress and battery cover
is on the back.
Battery holders that snap when you try to change the battery (not that
I'm expecting to change this on a re-chargeable one)
and then there's the batteries (Lithium, or something else) which one
do you choose and why?
They use a non-rechargeable battery.
I heard that some have a "sleep mode" you can activate whilst you're
cooking dinner. Are these any good ?
No need. Use the correct detector, which won't give a false alarm
(weorks on heat rise rate rather than smoke).
 
J

Jim Alexander

ac1951 said:
Lots of useful information ..
many thanks.

Not much on recommended models though ?
Reason for asking is:
Installed Ei140 series several years ago.

http://www.eielectronics.com/p1.php

Don't recall any installations problems. Installed on a dedicated circuit
without power failure detection. If I fail to notice the green led is not
on then backup battery operates it until it beeps on a depleted battery
according to the instructions. They have worked on the few occasions
tested.

Jim A
 
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A

Andrew May

Gel said:
I used the Kidde ones from TLC. No problems yet.

Fire alarms seem to be one of those instances where the ODPM has shot
itself in the foot with Part P. Installing on a dedicated circuit is
preferable but require building control notification and inspection if
you are doing it yourself. Adding to an existing lighting circuit does
not. You could get an further four alarms with whatever additional
protection that that may provide for the price of the
notification/inspection.

Andrew
 
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