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Control
Equipment
The Fire Alarm Control
Equipment should normally be sited in an area as follows:
Preferably in an area of
low fire risk and on the ground floor by the entrance
used by the Fire Brigade and preferably viewable from
outside of the building. It should be located in an
area common to all building users and where automatic
detection is in use, the Control Panel should be in
a protected area. An alarm sounder should be sited
next to the Control Unit, but not too near the telephone
position.
A suitable zone chart of
the building should normally be installed adjacent to
the Control Panel.
Power
Supplies
Two power supplies are required
ie: mains and battery and these are normally built into
the Fire Alarm Control Panel. Standby batteries must
allow the system to operate without mains for 24 hours
longer than the building is likely to be unoccupied
and then support the sounders for an additional half
hour. If the mains supply is supported by an emergency
generator then six hours standby plus half an hour alarm
load is sufficient. All modern Fire Alarm Systems are
24 volts.
On the medium and larger
sized Fire Alarm Systems, the standby batteries will
often not fit within the Control Panel. Where standby
batteries are contained within a separate housing, then
this housing must be as close as possible to the main
Fire Alarm Control Panel. If the power supply or battery
housing is located more than 10 metres from the main
Fire Alarm Control Panel then serious volt drop problems
can arise. Standby batteries are invariably of the
sealed lead acid variety. Use of nickel Cadmium Batteries
is not cost effective and automotive batteries must
not be fitted.
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Fire
Compartments
Buildings are normally
split into fire compartments with each compartment so
constructed as to prevent the spread of fire from one
compartment to another.
Each floor and each stairwell
within a building is normally a separate fire compartment.
Within a small factory, the factory unit will normally
be separated from the offices by >firewalls= to prevent the spread of smoke and fire from one to the
other. The factory and offices will therefore be in
separate fire compartments. A zone should normally
only cover a single fire compartment.
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Zoning
If the total floor area
(ie: the total of the floor areas of each floor of the
building) is not greater than 300 square metres then
the building need only be one zone, no matter how many
floors it has.
In general, if the total
floor area is greater than 300 square metres, then each
floor should be a separate zone (or set of zones, if
the floor is big enough).
There are two exceptions:
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| A |
If the building is sub divided into fire
compartments, then any compartment communicating with
other compartments only at the lowest level of the building
can be treated as if it were a separate building ie: if
a floor area is not greater than 300 square metres then
it can all be one zone, irrespective of the number of
storeys. |
| B |
Where stairwells or similar structures extend
beyond one floor, but are in one fire compartment, the
stairwell should be a separate zone. |
| There are two restrictions on the maximum
size of a zone, irrespective of the size of the building |
| A |
Its total Floor area should not exceed
2000 square metres |
| B |
The search distance should not exceed 30
metres. This means that a searcher entering the zone
by the normal route should not have to travel more than
30 metres after entering the zone in order to see a fire
big enough to operate a detector, even if the fire is
only visible from the extreme end of his search path.
Remote indicators show an alarm in a closed area and their
fitting can enable larger areas to comply to the search
distance requirements. |
| There are two restrictions on the configuration
of a zone, irrespective of its size. |
| A |
If the zone covers more than one fire compartment,
then the zone boundaries should follow compartment boundaries |
| B |
If the building is spilt into several occupancies,
then each occupancy should lie within a separate zone
(or set of zones), no zone should be split between two
occupancies |
Recommended
Cable Types
All cables used in Fire
Alarms must have a minimum conductor size of 1.0mm squared.
BS5839 Part 1, recommends
11 types of cable which may be used on a Fire Alarm
System where prolonged operation in a fire is not required.
Therefore 1.0mm twin and earth cable for instance, may
be used on detection circuits of Conventional Fire Alarm
Systems and the detection loops of Addressable and Analogue
Systems providing sounders are not connected to them.
Only two types of cable
may be used on Fire Alarm Circuits where prolonged operation
in a fire is required.
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| 1 |
Mineral - insulated copper - sheath cables
(MICC) complying with BS6207 |
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AND
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| 2 |
Cables complying with BS6387, and meeting
at least the requirements of categories AWX or SWX |
| In other words, on sounder circuits
and for wiring between a power supply and or battery housing
and the main fire alarm control panel you must use one
of the following types of cable. |
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MICC, Flamsil, Firetuff or similar
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On Addressable and Analogue
Addressable Fire Alarm Systems we would recommend the
use of a screened cable such as BICC Flamsil or Firetuff
or MICC for all wiring so as to minimise the possibility
of interference being picked up by or being transmitted
by the data loops.
In the larger buildings
within the London area (old section 20 buildings) only
bare MICC cable is often specified.
In summary therefore MICC
cable used for all your fire alarm wiring would be acceptable
anywhere. However, ordinary twin and earth 1.0mm cable
may be used on detection circuits of Conventional Systems
in certain circumstances.
As far as possible, joints
should be avoided except where a joint is inside one
of the systems components ie: Control Panel, detector,
Call Point, Sounder etc. Where joints are required
elsewhere they should be enclosed in a suitable junction
box marked fire alarm to ensure that the fire alarm
systems is not accidentally interfered with.
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Fire Alarm Cables, should
always be segregated from cables for other systems.
The segregation of MICC cables with a plastic sheath
is of course not so critical as the segregation of ordinary
twin and earth cable.
Installation of cables
should be in accordance with good practices recommended
in the latest edition of the IEE wiring regulations
Connection to the mains
supply should be via an isolating switch fuse reserved
solely for the purpose. Its cover must be painted red
and labelled A Fire Alarm - do not switch off@ .
Conductor size should take
voltage drop into account. In any case conductors should
have a cross sectional area of not less than 1 square
millimetre.
Where possible cables should
be routed through areas of low fire risk. Cables installed
in damp, corrosive or underground locations should be
PVC sheathed and where there is a risk of mechanical
damage should be protected accordingly. If Cables are
installed less than 2.25m above the floor should they
normally be protected.
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Volt
Drop in Cables
Unless a detection circuit
or detector loop exceeds 1 kilometre in length, it is
unlikely to give rise to a concern about volt drop.
If there are fairly long
sounder circuits or a sounder circuit has a large number
of Sounders, Buzzers, Voice Alarms or Flashing Beacons
etc on it, then voltage drops can cause problems. Providing
the overall volt drop does not exceed 4 volts on sounder
circuits then the system should operate satisfactorily.
The calculation of the precise
voltage drop at each point in the system is a long and
tedious calculation and way beyond the scope of this
guide. However, to get a rough idea as to whether a
system will operate satisfactorily one can use the following
calculations.
To start with we need to
know approximate volt drop characteristic of different
sizes of cable
1.0mm cable = 42mV per
amp per metre
1.5mm cable = 28mV per
amp per metre
2.5mm cable = 17mV per
amp per metre
4.0mm cable = 10mV per
amp per metre
6.0mm cable = 7mV per
amp per metre
If one is using 1.0mm cable
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Multiply 42 by
the length of the cable in metres |
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Multiply this by
the current of all the devices on the length of the cable |
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Divide the entire
figure by 1000 |
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This gives a rough idea
of the voltage drop.
Lets take an example where
you have 30 Sounders, each with a current consumption
of 20mA on 200 metres of 1.0mm cable.
If you were to wire in
1.0mm cable then the calculations would look something
like this:
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42 x 200
metres x 30 sounders x 0.02 amps
1000
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The answer is 5.04 volts.
This is more than the 4 volts previously discussed and
therefore we would suggest that 1.0mm cable would be
unsuitable in this instance.
Lets now try the calculation
using 2.5mm cable. In this instance we have the following:
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17 x 200
metres x 30 sounders x 0.02amps
1000
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| The answer is 2.04 volts.
A two volt drop is of course acceptable. |
Should you be on a budget
and be considering using 1.5mm cable, the answer after
making the calculation would be 3.36 volts and this
is indeed acceptable. However do not disclaim the possibility
that at a later date you may wish to add extra sounders,
and therefore you would be pushing the system to its
full limitations by utilising the 1.5mm cable.
You may encounter examples
where even 2.5mm cable is not sufficient. Rather than
use a larger cable which would be extremely difficult
to terminate in the rear of most sounders, it is usually
better to run additional sounder circuits and spread
the load.
Should you be using a remote
power supply or battery housing to power the control
panel, then the voltage drop becomes very significant.
As well as the consumption of the Control Panel, one
must consider the operating load of the sounders. It
is particularly important to keep voltage drop as low
as possible and preferably below 1 volt or power levels
will decrease even before you have commenced consideration
regarding the calculation of the volt drop to the sounders
from the control panel.
An example of this now
follows.
We have a control panel
which consumes 260ma and has a number of sounders connected,
which in total use 3amps in the alarm condition. If
you wired between the remote power supply and the control
panel which was only 20 metres away in 1.0mm cable then
the calculation would be as follows:
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42 x 20 metres
x 3.26 amps = 2.7 volt drop
1000xxxxxxxxx
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This would clearly be unacceptable.
Should we be able to locate
the remote power supply within 10 metres of the control
panel and wire it in 2.5mm cable the calculations should
look as so:
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17 x 10 metres
x 3.26 amps = just over half a volt
1000xxxxxxxxxxxxx
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The above example should
be acceptable. However when calculating the volt drop
on your sounder circuits it would be advisable not to
allow any volt drop to exceed 3.5 volts.
A word of warning however,
the writer of this guide has seen several examples where
electricians have installed cable that is too thin on
sounder circuits and consequently the system has encountered
substantial volt drops ie: in excess of 12. A way around
this has then been sought and the 24 volt bells have
been substituted with 12 volt bells. This does not
work, as if you lower the voltage the current increases
and so the problem gets worse.
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Routine
Testing of the System
The system should be regularly
tested and serviced and BS5839 Part 1 makes the following
recommendations:
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| DAILY |
Check that the panel indicates normal operation. If
not record any fault indicated in the event log and report
the fault to a responsible person. Check that any fault
recorded from the previous day has received attention. |
| WEEKLY |
Operate a manual call point or smoke detector to ensure
the system operates properly. Each week a different detector
or call point should be checked. Check that the sounders
have operated and then reset the system. Check the battery
connection. Any defect should be recorded in the log
book and reported. Action should be taken to correct
the defect. |
| QUARTERLY |
Check entries in the log book and take any necessary
action. Examine the batteries and their connections.
Operate a manual call point and smoke detector in each
zone to ensure that the system operates properly. Check
that all sounders are operating. Check that all functions
of the alarm control panel operate by simulating fault
conditions. Visually check that structural alterations
have not been made that could have an effect on the siting
of detectors and other trigger devices. Complete the
event log with details of the date, time, trigger device
tested and > Quarterly Test= in the event section. Any defects or
alterations to the equipment should also be entered |
| ANNUALLY |
Carry out an inspection as detailed for this quarterly
inspection. Every detector should be tested in site.
All cable fitting and equipment should be checked to ensure
that they are secure and undamaged. |
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A qualified engineer should
carry out the quarterly and annual inspections and issue
a certificate after each annual inspection. It is normal
practice for 1/4 of all detection systems to be cleaned
and checked on each quarterly visit so that the entire
system has been properly maintained after the fourth
visit.
Whilst the end user of
the fire alarm system may be expected to carry out the
daily and weekly functions very few would be adequately
equipped or trained to carry out the quarterly and annual
tests.
Photain Controls plc would
be please to submit a price for the maintenance of any
Fire Alarm System which has been installed using Photain
Fire Alarm Equipment.
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The intention of this guide is to keep
the information given as simple as possible.
This necessitates the omission of much information contained
within the various British Standards and the requirement of
the various fire acts.
Photain Controls can therefore not take any responsibility
for the way in which any information contained in this guide
is used.
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[1] |
If you extend or change a property, you
probably need a new or revised certificate |
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[2] |
With wiring type 1 and 2 as
detailed above, the amount of cable required will most
probably be increased and will raise the cost of the installation.
In addition if the first detector unit is removed then
none of the following devices would be operative. This
restriction would not apply to Type 3 as detailed |
| 3 BS5839 Part 1 Section 7.2 dictates this loss to be a maximum of 2000 square
metres of area protected -See section 7 on pages 11 -
12 of BS5839 for further details |
| [4] |
This is a British Standards Requirement |
| [5] |
Preferably on Exit Routes |
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