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Introduction

   Emergency lighting is light provided to come on when the mains fail. It is usually provided for safety reasons and may also be provided to enable the normal occupation of a building.
The most widely used and economical systems are stored energy systems using secondary batteries specifically designed for long term standby use.

Glossary Of Terms

BATTERY One or more cell, primary or secondary,inter-connected to from the standby power supply for an emergency lighting systems.
Central INVERTER An inverter for more than two lamps,operating remotely mounted luminaires. The output voltage and frequency and waveform may differ from a normal mains supply.

Central Unit System A system in which the batteries for a number of luminaires are housed in one location,sometimes for all of the luminires in a complete building,more usually for all of the luminaries on one lighting sub-circuit.

Emergency Exit An Exit which is intended to be used only during an emergency.

Emergency Lighting Lighting provided for use when the normal lighting fails.

Maintained Emergency Lighting A lighting system in which all emergency lighting lamps are in operation of all material times.There are two types of maintained systems. Changeover type or floating type.On the changeover type,the lamp will be switched, on mains failure,from the mains circuit to the battery circuit. On the maintained floating system, the lamp is operated from the same circuity at all times, normally from a transformer while mains is available and from the battery on mains failure.

Mounting Height The vertical distance between the luminaires and the working plane.
Note : For emergency lighting the floor is taken to be the working plane.

Non-maintained Emergency Lighting A lighting system in which all emergency lighting lamps are in operation only when the normal lighting fails.

Normal Lighting All permanently installed artificial lighting, operating from the supply, in normal use,which, in the absence of adequate daylight, is intended for use during the whole time that the premises are occupied.

Rated Duration The manufacturer's declared duration for a battery operated emergency lighting unit, specifying the time for which it will operated after mains failure. This may be for any reasonable period, but is normally one to three hours (when fully chargrd).

Re-charge Period The time necessary for the batteries to regain sufficient capacity to enable the lamp to perform its rated duration.

Spacing/height Ratio The ratio of spacing between the geometric centres of adjacent luminaires to their height above the working plane.

Self-contained Emergency Lighting The luminaire, complete with its own batteries,and integral circuitry requiring only the mains supply to be connected for its correct operation.

Battery Pack A circuit containing the elements necessary for operation of an emergency lighting lamp. This may include the battery charging circuit,the DC to AC inverter,tube ballasting and solid state changeover rely.

Design And Installation

   When designing an emergency lighting installation the following points must be considered.
   1. Purpose of emergency lighting,is it for escape or standby lighting?
   2. Design code: The most commonly used design code is EM, however, Some local authorities or specifying bodies may have their own Requirements and there should be consultation between the owner/Occupier of the premises,the architect or lighting engineer,the installation contractor and the enforcing authority before any decisions are finalised.

Design Requirements

(a) To indicate clearly and unambiguously the escape routes, generally by the use of Exit signs.
(b) To provide illumination along the escape routes in safety using luminaires spaced at the appropriate distances, say to illuminate fire alarm call points and fire fighting equipment.
(c) Where required to provide standby lighting, to permit safe occupation of the building.
(d) Where required to provide security lighting, to prevent injury to Persons or threats to property.

Example Of An Emergency Lighting Scheme

Practical Approach to Design Place all the essential escape route signs and luminaires near each exit door, emergency exit door, and at other hazard points as shown below.
a) Near each intersection of corridors;
b) Near each exit door;
c) Near each change of direction (other than on a staircase);
d) Near each staircase so that each flight of stairs receives direct light;
e) Near any other change of floor level;
f) Outside each final exit and close to it;
g) Near each fire alarm call point;
h) Near fire fighting equipment;
i) Exit and safety signs required by the enforcing authority;

Note : For the purposes of this clause 'near' is normally considered to be within 2m measured horizontally.

Advantages Of Self Contained Systems

   Also known as Single Point Systems, are Emergency Lighting or Exit Signs whereby the battery pack are built into each emergency luminaires individually.In this instance if a fire in a certain location destroy one or several of the emergency luminaires it will not affect any of the other emergency luminaires in other locations because the emergency supply is not powered by a common source as in the case of Central System.Self Contained Luminaires are available for operating low-voltage tungsten lamps up to 50 watts.2-pin PL or PLC energy-saving lamps and fluorescent tubes up to 80 watts.

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