Martin Carroll wrote:
In article , John Rumm
writes
tony sayer wrote:

1.19 The power supply for a smoke alarm system should be derived from
the dwellinghouse's mains 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 the
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'm just doing 1st fix on the current job and was reading about this
just the other day. I was puzzling over the "There should be a means of
isolating power to the smoke alarms without isolating the lighting". I
am not sure how this may be achieved?

Cheers

Martin


I know nothing, but have a look he

http://www.tlc-direct.co.uk/Products/TLCT100C.html

The wording of the description suggests that it could be used in the
situation you describe. (I rather hope someone else, someone who knows
something, comes along in a minute and agrees or disagrees.)

--
Rod

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onset.
Although common it frequently goes undiagnosed.
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Martin Carroll wrote:
In article , John Rumm
writes
tony sayer wrote:

1.19 The power supply for a smoke alarm system should be derived from
the dwellinghouse's mains 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 the
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'm just doing 1st fix on the current job and was reading about this
just the other day. I was puzzling over the "There should be a means of
isolating power to the smoke alarms without isolating the lighting". I
am not sure how this may be achieved?

If you take your feed to the first alarm via a DP switch close to the
CU, and then feed the switch from the same breaker as the lighting
circuit then you can meet the requirement.

You could also do something similar from a ceiling rose position, again
via a DP switch.

Subsequent alarms can be powered from the first via a 3&E that also
carries the interlink signal.

--
Cheers,

John.

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Rod wrote:
Martin Carroll wrote:
In article , John Rumm
writes
tony sayer wrote:

1.19 The power supply for a smoke alarm system should be derived
from the dwellinghouse's mains 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 the 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'm just doing 1st fix on the current job and was reading about this
just the other day. I was puzzling over the "There should be a means of
isolating power to the smoke alarms without isolating the lighting". I
am not sure how this may be achieved?

Cheers

Martin


I know nothing, but have a look he

http://www.tlc-direct.co.uk/Products/TLCT100C.html

The wording of the description suggests that it could be used in the
situation you describe. (I rather hope someone else, someone who knows
something, comes along in a minute and agrees or disagrees.)

It would meet the requirement for isolation, however it would also end
up tucked into a ceiling void somewhere and hence would not be that
convenient for maintenance purposes.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article , John Rumm
scribeth thus
tony sayer wrote:

In the cases where alarms are required (like a loft conversion adding a
third storey) then you then must use battery backup alarms if you are
powering them from a non dedicated circuit.

Is that strictly the case that they MUST be battery backed on anything
other then a dedicated circuit?..

That was my experience based on the building regs a the time I did my
loft conversion. However I have just had a read through the current version:

http://www.planningportal.gov.uk/upl..._ADB1_2006.pdf

One of the commented changes is that all alarms should now have a backup
power supply.

The current wording is:

"Power supplies

1.19 The power supply for a smoke alarm system should be derived from
the dwellinghouse's mains 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 the
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.

So thats an unusual bit of wiring around the CU then?..

1.20 The electrical installation should comply with Approved Document P
(Electrical safety).

1.21 Any cable suitable for domestic wiring may be used for the power
supply and interconnection to smoke alarm systems. It does not need any
particular fire survival properties except in large houses (BS
5839-6:2004 specifies fire resisting cables for Grade A and B systems).
Any conductors used for interconnecting alarms (signalling) should be
readily distinguishable from those supplying mains power, e.g. by colour
coding.


Now what way do they want that done and what colour?..

Note: Mains-powered smoke alarms may be interconnected using
radio-links,

Scary .. absolutely scary...

provided that this does not reduce the lifetime or duration
of any standby power supply below 72 hours. In this case, the smoke
alarms may be connected to separate power circuits (see paragraph 1.19)

1.22 Other effective options exist and are described in BS 5839-1:2002
and BS 5839-6:2004. For example, the mains supply may be reduced to
extra low voltage in a control unit incorporating a standby
trickle-charged battery, before being distributed at that voltage to the
alarms."

The logic being that alarms
alone are highly unlikely to trip a circuit,

No I very much doubt they would, and seeing there're not earthed
even..

Indeed.

whereas a shared circuit
might be tripped by something else and lose the alarms.

Yes but that would be noticed very quickly..

Perhaps, although on a summers day you could go many hours unprotected...

Most mains
powered alarms also have a "mains on" LED so you can see at a glance if
they are not powered.

Yep so they might .. but take the case of a HIMO do you really think
that say some 20 odd year old house sharers would even look?..
Under the 16th edition regs one would have likely placed alarms on a non
RCD protected circuit. IMO they are probably still better powered that
way when a dedicated circuit is in use, but with a suitably screened cable.

Screened against what?..

Screened so as to provide earthed enclosure of the cable. i.e. to meet
17th edition requirements for the protection of cables, where you can
only have a non RCD protected cable hidden in the fabric of the
building if it =50mm from the surface, or run in a cable like MICC,
Earthshield, SWA etc.

Hummmm.....

I don't think they have thought this out all that carefully...



--
Tony Sayer

tony sayer wrote:

The current wording is:

"Power supplies

1.19 The power supply for a smoke alarm system should be derived from
the dwellinghouse's mains 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 the
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.

So thats an unusual bit of wiring around the CU then?..

Not especially - its not uncommon to provide isolating switches for all
sorts of appliances of even clusters of appliances. For example you may
have all your outside lights powered from the downstairs lighting
circuit, but with an isolator that enables them to be independently
turned off. As long as you label the switch, all should be clear. (in
fact a keyswitch might be a good idea here)

The intention being that you can work on the alarm circuit and not have
to turn off all the lights to do so.

1.20 The electrical installation should comply with Approved Document P
(Electrical safety).

1.21 Any cable suitable for domestic wiring may be used for the power
supply and interconnection to smoke alarm systems. It does not need any
particular fire survival properties except in large houses (BS
5839-6:2004 specifies fire resisting cables for Grade A and B systems).
Any conductors used for interconnecting alarms (signalling) should be
readily distinguishable from those supplying mains power, e.g. by colour
coding.


Now what way do they want that done and what colour?..

Personally I would treat the interlink wire as a switched live[1] - much
as you would treat the return from a switch. Hence flag it with brown
sleeve on a harmonised colour 3&E, or red on a old colour one.

[1] Which for most alarms it probably is - although one should allow for
the possibility that it may carry proprietary signalling with some
brands of alarm.

Note: Mains-powered smoke alarms may be interconnected using
radio-links,

Scary .. absolutely scary...

Seems to work ok for thermostats... ;-)

Screened against what?..

Screened so as to provide earthed enclosure of the cable. i.e. to meet
17th edition requirements for the protection of cables, where you can
only have a non RCD protected cable hidden in the fabric of the
building if it =50mm from the surface, or run in a cable like MICC,
Earthshield, SWA etc.

Hummmm.....

I don't think they have thought this out all that carefully...

Why so?

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

We are doing a similar project and on certain doors have added
electromagnetic catches linked to the detectors, so that the doors can
be kept open but will automatically close if the alarm is triggered.
The weirdest side effect is that the first indication I had of a day-
time power cut was the sound of doors slamming shut.

Jonathan