Electrical Lighting in the Home
Light in the home is usually taken for granted. The basic types of house lighting, using modern long-life cables, are the loop-in and junction box methods. The number of house-circuits is partly a matter of convenience but also a question of load. Lighting circuits can offer convenience and versatility, with two- or multi-way switching arrangements.
Lighting wiring circuits follow two general patterns: the loop-in system, where power is taken in turn to ceiling roses, or by 5A junction boxes, from which each ceiling rose and wall switch is individually connected.
Twin-with-earth 1mm2 cable with a 6A rating should be used. This can be loaded up to 1400W. If heavier loads are used, then they must be sub-divided into smaller units and run from separate circuits. Normally, one circuit on each floor of an average house is sufficient.
Assuming an average consumption of 100W for every lighting outlet, the maximum number of lighting points for each 5A circuit is 11.
The most important safety consideration is correct earthing – so that, if a short circuit occurs, will direct itself safely to earth.
An earth-continuity conductor (ECC) in the cable should be run to all terminal points in a lighting circuit-ceiling roses and switches-whether these are insulated or not.
This ensures that an earthing point, which must be used for metal switch or lighting fittings, is available if later needed.
Earthing is essential to provide protection from faults, and all protective metal parts in a circuit must be earthed.
When a live part of the circuit comes into contact with an earthed part, the electricity is conducted away. This causes a fuse to blow, which indicates a fault.
The term ‘consumer’s earth terminal’, indicates that connections are to a direct earthing point or an earth leakage circuit-breaker. This should be tested at intervals and also when any new wiring is carried out.
A simple circuit tester can be made using a torch battery and a bulb. Do not use this on live wires or on equipment which is plugged into the power supply; always switch off the supply before testing.
You need a panel of wood a little longer and wider than a standard torch battery. The battery can be clamped around this with rubber bands. Fit a bulb holder and bulb on to the panel and solder the live terminal of the battery to one side of the holder.
Attach a length of wire, with a probe or a crocodile clip at the end, to the other side of the holder. Similarly, attach a terminal to the other plate of the battery.
If the bulb lights when the probes are connected across the neutral and earth points, this indicates an earth leak which must be corrected.
There is either a breakdown in cable insulation, causing wires to touch or a loose or incorrect connection at a switch or other terminal.
House circuits have two supply conductors and an earth conductor. Of the supply conductors one is live (L). All fuses, switches or circuit breakers are placed in this lead. The other, neutral (N), is at, or near, earth potential. The third is the earth (E) lead.
No switches, fuses or circuit breakers should be placed in the neutral and earth leads Flexible cables are colour coded as follows:
Fixed cables are coded:
Earth-Green or unsheathed
Always follow this code when wiring electrical circuits.
All plugs must be protected by fuses which should be fitted into the live (brown flexible cable) side of the circuit. In fixed cables, the fuse is in the red cable.
You must use fuses of the correct current rating in the consumer unit as well as in plugs. Each lighting circuit must have its own fuse.
There are two types of fuse: the cart ridge and the re-wirable types. In some cases, fuses may be replaced by miniature circuit breakers (MCB) in the consumer units. The fuses must then be installed in control or distribution units.
10. November 2011 by admin
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