This cable calculator is to be used as a guide only; the cable sizes are worked out using information given from your input, accurate values are essential to give you the correct cable size. The user is to ensure the type of cable is suited to environment and conditions the cable will be exposed to.
This cable calculator is set for Installation method C (Clipped Direct), for cable types BS5467 and BS6724 SWA (Steel wire armoured cable) and is based on the voltage drop selected at 230V single phase and 400V three phase.
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Fire Rated Down Lights Guide
Down lights and fire safety
This guide provides a quick reference for installers on
the appropriate selection and installation of fire rated down lights
in domestic premises, and on how to prevent them
from becoming a fire hazard.
1. Introduction to fire rated down lights
Poorly installed down lighters (recessed luminaires) is the cause of a significant number of fires in
homes every year. This guide provides a quick reference for installers on the appropriate selection and
installation of down lighters in domestic premises, and on how to prevent them from becoming a fire
2. Why is down lighters a fire risk?
• Under normal operating conditions, the surface temperature of tungsten halogen lamps can
exceed 200 ºC, which is above the ignition temperature of many combustible materials.
• Without adequate ventilation to permit safe heat dissipation, down lighters not designed to be
covered by thermal insulation, or installed too close to combustible materials (such as roof
timbers) can cause fires or harmful thermal
effects to their surroundings.
• Even when insulation is not present, there is a
risk that dust, debris and other potentially
combustible materials could ignite if they come
into contact with the hot lamp.
• Overheating can occur where thermal insulation
is laid over existing down lighters and any
associated transformers that are not designed to
operate safely under these conditions.
• The bases of the most common types of push-fit
extra-low voltage lamps (with aluminum or
diachronic reflectors) are identical (see section 4 for diagrams). However, most types of
down lighter are not designed to operate safely with both types of lamp. Consequently, lamps
can be fitted inadvertently that exceed the maximum rating of the luminaries or which reflect
heat in the wrong direction.
3. Fire rated down lights explained
Down lighters operate at mains voltage (230 Volts), or are powered via a transformer at extra-low voltage
(12 Volts). Extra-low voltage (ELV) down lighters are often incorrectly described as “low voltage” on
Down lighters may also be described as ‘Fire rated’. This means they have in-built fire protection that
Completely seals the down lighter in the event of fire in the room below, to prevent the spread of fire and
Smoke into other areas.
It is important that the fire performances of ceiling structures that have fire containment function or are
Required to carry load for a prescribed period of time are not compromised by the installation of
For ALL down lighters installed in ceilings, the Electrical Safety Council recommends the use of ‘fire rated’
Down lighters fitted with ‘aluminum’ reflector lamps to help ensure that any fire in the space below is
Kept out of cavities and that the heat build-up above and within the fitting is minimized.
Typical fully closed back ‘fire rated’ down lighter typical standard open back down lighter
In situations where a selected design or style of down lighter is not available with integral fire protection,
additional protection may be fitted at the time of installation in the form of
A purpose made ‘fire hood’, an insulated fire protection box, or similar.
Detailed guidance on the selection of suitable types of down lighter for
Particular applications is given in the Electrical Safety Council’s Best
Practice Guide 5 – Electrical installations and their impact on the fire
Performance of buildings.
Mounting on normally flammable surfaces
Down lighters are classified according to whether or not they are
Suitable for direct mounting on normally flammable surfaces.
‘Normally flammable’ materials are those which have an ignition
temperature of at least 200 °C and which will not deform or weaken
at this temperature. Examples are wood and wood-based materials
of more than 2 mm thickness.
Where a down lighter is suitable for direct mounting on
non-combustible surfaces only, either of these warning symbols
should be marked on the fitting.
Covering with thermal insulating materials
To avoid the risk of fire (as well as reduced lamp and service life) caused
by overheating, down lighters and any associated transformers must not
be covered by thermal insulation and need to be protected against
potential or future covering, unless they are specifically designed to
operate safely in this condition. Particular care must be taken where
loose-filled insulation is present, as this can be moved easily by drafts,
vermin, etc, and may then come into contact with the down lighter.
Down lighters marked with
Are suitable for covering with thermal insulation
Must not be covered with thermal insulation
Building Regulations do not prohibit the leaving of a small area around down lighters free from thermal
insulation where this is necessary to permit the dissipation of heat they generate. However, due
allowance for this should be made in the overall thermal and acoustic performance of the premises.
Alternatively, where access to the space above the down lighter can be achieved.
typical insulation support box Loft cover
In all cases, the manufacturer’s instructions supplied with the down lighter must be followed. The
manufacturer should specify, amongst other things, the amount of space to be left around the back of
the down lighter, its fire rating, whether the fitting can be covered with thermal insulation, and the
type/wattage of lamps that can be fitted.
ingress protection (iP) rating
Down lighters should be selected with the correct IP rating for the location in which they are to be
installed. For example, those located in bathrooms should have an IP rating based on the zone they are
installed in. In all cases, account must be taken of the requirements given in the current version of
BS 7671 (Requirements for Electrical Installations, IEE Wiring Regulations 17th Edition), the national standard
for the safety of electrical installations.
4. Down lighter lamps explained
The most widely available types of tungsten halogen lamp are manufactured with either a dichroiccoated
(cool beam) reflector or an aluminum reflector. The reflector type determines the way in which
most of the heat generated by the lamp is reflected.
Diachronic (cool beam) lamps reflect visible light forwards while allowing most of
the radiated heat to pass out of the back of the lamp – Warning: these lamps
must only be used in down lighters specifically designed for their use, otherwise
overheating can occur.
Aluminum lamps reflect the visible light and most of the heat forwards out of the
front of the lamp. However, consideration must be given to the positioning and
intended use of down lighters fitted with aluminum reflector lamps to prevent
excessive heating of lighted objects.
The most common tungsten halogen lamps for use in down lighters are push fit (GU4 or GU5.3) for ELV,
or twist and lock (GU10 or GZ10) for mains voltage types.
ELV lamp bases Mains voltage lamp bases
Although lamp bases are different in design to prevent ELV lamps being used in mains voltage fittings,
GU4, GU5.3 and GZ10 lamp holders will accept both aluminum and diachronic reflector lamps. the use of
diachronic reflector lamps in down lighters designed for use with aluminum reflector lamps only
could create excessive heat within the luminaire leading to an unsafe situation and risk of fire.
Down lighters marked with this warning symbol Must not be fitted with
diachronic reflector lamps.
4 mm 5.3 mm
10 mm 10 mm
Tungsten halogen lamps must be fitted with a protective shield (a
glass plate in front of the halogen filament) to ensure that particles
from a shattered lamp cannot cause harm. Down lighter fittings not
supplied with a glass protective shield must be fitted with a ‘self shielded’
5. Safety symbols, information and markings
The relevant product standards relating to luminaries and associated control equipment specify safety
information that manufacturers must mark on down lighters, lamps and associated transformers, or
A recent revision of the product standard relating to luminaries (BS EN 60958-1) has resulted in some
symbols and markings having been changed to align with current international (IEC) standards. All the
provisions of the revised ‘2008 edition’ of BS EN 60958-1 are required to be implemented by April 2012.
As a result of the transitional arrangements, down lighters may be sold and marked with both old
and/or new symbols and information.