Many buildings must have some form of emergency lighting to come on if the electric
supply to the ordinary lights fails. BS 5266: Emergency lighting, BS EN 1838, BS 5266–
7: Lighting applications. Emergency lighting are the codes of practice to which to refer.
One of the possible causes of failure is a breakdown in the supply authority’s service to
the building and, therefore, the emergency supply must be independent of the service into
the building.
Electric lighting for emergency use can be provided if the building has a standby
generator. A generator can be installed to take over the entire supply to a building, so that
the only special provision for emergency lights need made is to cover the time between
the mains supply fails and the standby generator is up to speed, but for economy the
standby generator is often rated at less than the ordinary mains service to the building.
The distribution then has to be arranged so that only a part of the service within the
building is fed by the generator, and only a few of the lights should be included in this
part. There is no need for full lighting under emergency conditions, and lighting in the
main corridors and staircases is usually enough. High risk task areas need special
consideration.
Emergency supplies are of particular importance in hospitals and no new hospital
should be built without a standby generator, but buildings like schools, offices, theatres
and blocks of flats seldom justify the expense. For these buildings emergency lighting is
almost invariably provided, by self-contained battery luminaires.
Emergency lights are fitted throughout the building. They come on only when the
mains fail (a non-maintained system) and cannot be used while the mains are healthy.
They are not intended to give full illumination, but only
Figure 7.14 Central emergency system
to provide sufficient light for people to make their way out of the building safely. A
minimum of 1 lux should be achieved, and 5 lux near fire-fighting equipment.
Emergency lighting in high-risk task areas such as near hot vats should have an
illumination of 10 lux. Manufacturers’ data will give luminaire spacings at given heights
to achieve these lighting levels. One light on each landing and perhaps one in the centre
of any particular corridor should be perfectly adequate. A number of low-power
luminaires is generally better than one large luminaire. These lights work on low voltage
d.c. and are fed from a battery. A trickle charger permanently connected to the mains
ensures that the battery is always fully charged. The lights are cabled from the battery
through a relay, the contacts of which are closed when the coil is de-energized. The coil
is fed from the mains and as long as the mains are on, the contacts are held open. Thus as
long as the main supply is healthy, the battery lighting circuit is kept open, but
immediately the mains fail the relay contacts close and the emergency lights come on.
The circuit diagram is given in Figure 7.14.
There are battery chargers and relays purpose-made for this kind of application. The
charger must be left permanently switched on, and contains the relays necessary to stop
the charging current when the battery is at full charge. It can be supplied by a final circuit
from any convenient distribution board, but there should be no other outlets on the same
final circuit. Alternatively, it can be fed directly from a switch fuse at the main intake.
Because the emergency lights work at a low voltage, the voltage drop in the cable to
them can become considerable and may present something of a problem. Whereas a 60W
bulb on a 230V supply takes 0.26A, a 24W bulb on a 24V supply takes 1.0A and the
voltage drop in a cable of a given size is about four times as great. At the same time, a
drop in a cable of 2.4V in 230 may reduce the light output by perhaps 2 per cent but the
same drop of 2.4V in a 24V system is proportionately ten times as great and could reduce
the light output by a fifth or a quarter. Low-voltage cables must, therefore, be adequately
sized. It is in any case inadvisable to design an emergency system for less than 48V d.c.,
which is a convenient standard battery-output voltage. Even with a 48V system and
ample cable sizes, there must obviously be a limit to the number of lights which can be
served from one battery and to the distance the furthest light can be from the battery. A
large building may, therefore, need several separate battery systems. Legislation has
made it more essential to provide lights to mark fire-escape routes from buildings. The
lights used for this are of very low wattage and, consequently, the voltage-drop problems
are somewhat eased.
The emergency lights themselves are ordinary luminaires which take a low-voltage
d.c. bulb. These are very energy expensive, and using a fluorescent through an inverter
will reduce the current required by the circuit. There is a more common method of
emergency lighting which makes use of special luminaires, each of which contains its
own battery, charger and relay. The luminaire effectively houses a complete low-voltage
system just large enough to operate one light. The use of such luminaires makes it
unnecessary to run a low-voltage circuit throughout the building. With this system, the
emergency luminaires are put in the most suitable places for emergency illumination and
are fed from any convenient lighting circuit. In some cases, it may be convenient to have
two or three emergency lights on a circuit of their own and in other cases, it may be
convenient to have an emergency light included in one of the normal lighting circuits.
Such self-contained emergency luminaires are made in a variety of shapes and with a
variety of light sources. They may be incandescent, fluorescent light, or LEDs and can
take the form of illuminated signs. An emergency light with the word ‘EXIT’
supplemented with pictograms has an obvious application, although pictograms without
the use of text are now preferred. They are usually on at all times that the building is
occupied (maintained system). It has been known that the maintained lights are supplied
through a relay which is controlled from the burglar alarm system, so that the lights are
off when the building is unoccupied. Examples of emergency lights are illustrated in
Figure 7.15. An important advantage of these self-contained luminaires is that they
require little maintenance although the battery lifespan is limited and the standard on
emergency lighting BS 5266–1 gives requirements for testing the system, and requires
that the three yearly test be carried out annually for batteries over three years old. It also
stipulates minimum lighting levels for the emergency lighting. Modern luminaires of this
type may include a self-monitoring facility. Another advantage is that locally supplied
Lighting 125
emergency luminaires will respond to a local outage of supply, whereas a central system
will only respond to a mains supply failure.
Hazardous area luminaires
The principles on which hazardous area accessories are designed are explained in Chapter
1. Most types of luminaire are also available in hazardous area versions. When these are specified, it is important to make sure that the ones selected are suitable for the zone and
group appropriate to the area in which they are to be fitted.
Standards relevant to this chapter are:
BS 559 Electric signs and high voltage luminous discharge tube installations
BS EN 60400 Lamp holders for tubular fluorescent lamps and starter holders
BS 5266 Emergency lighting
BS EN 1838, BS 5266–7 Lighting applications; emergency lighting
BS 5499 Exit signs
BS EN 60598–1 Luminaires
BS EN 61184 Bayonet lampholders
supply to the ordinary lights fails. BS 5266: Emergency lighting, BS EN 1838, BS 5266–
7: Lighting applications. Emergency lighting are the codes of practice to which to refer.
One of the possible causes of failure is a breakdown in the supply authority’s service to
the building and, therefore, the emergency supply must be independent of the service into
the building.
Electric lighting for emergency use can be provided if the building has a standby
generator. A generator can be installed to take over the entire supply to a building, so that
the only special provision for emergency lights need made is to cover the time between
the mains supply fails and the standby generator is up to speed, but for economy the
standby generator is often rated at less than the ordinary mains service to the building.
The distribution then has to be arranged so that only a part of the service within the
building is fed by the generator, and only a few of the lights should be included in this
part. There is no need for full lighting under emergency conditions, and lighting in the
main corridors and staircases is usually enough. High risk task areas need special
consideration.
Emergency supplies are of particular importance in hospitals and no new hospital
should be built without a standby generator, but buildings like schools, offices, theatres
and blocks of flats seldom justify the expense. For these buildings emergency lighting is
almost invariably provided, by self-contained battery luminaires.
Emergency lights are fitted throughout the building. They come on only when the
mains fail (a non-maintained system) and cannot be used while the mains are healthy.
They are not intended to give full illumination, but only
Figure 7.14 Central emergency system
to provide sufficient light for people to make their way out of the building safely. A
minimum of 1 lux should be achieved, and 5 lux near fire-fighting equipment.
Emergency lighting in high-risk task areas such as near hot vats should have an
illumination of 10 lux. Manufacturers’ data will give luminaire spacings at given heights
to achieve these lighting levels. One light on each landing and perhaps one in the centre
of any particular corridor should be perfectly adequate. A number of low-power
luminaires is generally better than one large luminaire. These lights work on low voltage
d.c. and are fed from a battery. A trickle charger permanently connected to the mains
ensures that the battery is always fully charged. The lights are cabled from the battery
through a relay, the contacts of which are closed when the coil is de-energized. The coil
is fed from the mains and as long as the mains are on, the contacts are held open. Thus as
long as the main supply is healthy, the battery lighting circuit is kept open, but
immediately the mains fail the relay contacts close and the emergency lights come on.
The circuit diagram is given in Figure 7.14.
There are battery chargers and relays purpose-made for this kind of application. The
charger must be left permanently switched on, and contains the relays necessary to stop
the charging current when the battery is at full charge. It can be supplied by a final circuit
from any convenient distribution board, but there should be no other outlets on the same
final circuit. Alternatively, it can be fed directly from a switch fuse at the main intake.
Because the emergency lights work at a low voltage, the voltage drop in the cable to
them can become considerable and may present something of a problem. Whereas a 60W
bulb on a 230V supply takes 0.26A, a 24W bulb on a 24V supply takes 1.0A and the
voltage drop in a cable of a given size is about four times as great. At the same time, a
drop in a cable of 2.4V in 230 may reduce the light output by perhaps 2 per cent but the
same drop of 2.4V in a 24V system is proportionately ten times as great and could reduce
the light output by a fifth or a quarter. Low-voltage cables must, therefore, be adequately
sized. It is in any case inadvisable to design an emergency system for less than 48V d.c.,
which is a convenient standard battery-output voltage. Even with a 48V system and
ample cable sizes, there must obviously be a limit to the number of lights which can be
served from one battery and to the distance the furthest light can be from the battery. A
large building may, therefore, need several separate battery systems. Legislation has
made it more essential to provide lights to mark fire-escape routes from buildings. The
lights used for this are of very low wattage and, consequently, the voltage-drop problems
are somewhat eased.
The emergency lights themselves are ordinary luminaires which take a low-voltage
d.c. bulb. These are very energy expensive, and using a fluorescent through an inverter
will reduce the current required by the circuit. There is a more common method of
emergency lighting which makes use of special luminaires, each of which contains its
own battery, charger and relay. The luminaire effectively houses a complete low-voltage
system just large enough to operate one light. The use of such luminaires makes it
unnecessary to run a low-voltage circuit throughout the building. With this system, the
emergency luminaires are put in the most suitable places for emergency illumination and
are fed from any convenient lighting circuit. In some cases, it may be convenient to have
two or three emergency lights on a circuit of their own and in other cases, it may be
convenient to have an emergency light included in one of the normal lighting circuits.
Such self-contained emergency luminaires are made in a variety of shapes and with a
variety of light sources. They may be incandescent, fluorescent light, or LEDs and can
take the form of illuminated signs. An emergency light with the word ‘EXIT’
supplemented with pictograms has an obvious application, although pictograms without
the use of text are now preferred. They are usually on at all times that the building is
occupied (maintained system). It has been known that the maintained lights are supplied
through a relay which is controlled from the burglar alarm system, so that the lights are
off when the building is unoccupied. Examples of emergency lights are illustrated in
Figure 7.15. An important advantage of these self-contained luminaires is that they
require little maintenance although the battery lifespan is limited and the standard on
emergency lighting BS 5266–1 gives requirements for testing the system, and requires
that the three yearly test be carried out annually for batteries over three years old. It also
stipulates minimum lighting levels for the emergency lighting. Modern luminaires of this
type may include a self-monitoring facility. Another advantage is that locally supplied
Lighting 125
emergency luminaires will respond to a local outage of supply, whereas a central system
will only respond to a mains supply failure.
Hazardous area luminaires
The principles on which hazardous area accessories are designed are explained in Chapter
1. Most types of luminaire are also available in hazardous area versions. When these are specified, it is important to make sure that the ones selected are suitable for the zone and
group appropriate to the area in which they are to be fitted.
Standards relevant to this chapter are:
BS 559 Electric signs and high voltage luminous discharge tube installations
BS EN 60400 Lamp holders for tubular fluorescent lamps and starter holders
BS 5266 Emergency lighting
BS EN 1838, BS 5266–7 Lighting applications; emergency lighting
BS 5499 Exit signs
BS EN 60598–1 Luminaires
BS EN 61184 Bayonet lampholders
No comments:
Post a Comment