In modern homes in the UK, understanding domestic electric lighting circuits is crucial. These circuits are separate from the power ring main circuit and typically consist of at least two lighting circuits, each protected by a 5 amp fuse or 6 amp trip in the consumer unit. It is common to have one lighting circuit for each floor, even if the number of lamps on each level is less than 12.

Lighting Cable

Unlike the ring power circuit, the lighting circuit does not form a loop returning to the consumer unit. Instead, the consumer unit is usually connected to the first lamp, which is then linked to the second lamp, and so on. The cable used in lighting circuits is a 1sq mm PVC twin core and earth rated for up to 12 amps. It has a red insulated core for live, a black insulated core for neutral, and a bare earth conductor between them. These conductors are laid side by side within a PVC sheath. When connecting the cable, the exposed earth connector needs to be covered with a yellow and green sleeve to denote that it is an earth.

The lighting cable is routed from the consumer unit to a series of lighting points, such as ceiling roses or wall light fittings. The power to each lamp is connected via a wall or ceiling-mounted switch. Some light units have their own switch, in which case the power circuit is connected directly to the fitting.

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Light Switches

Most room lights are controlled by wall-mounted toggle switches, but touch-sensitive or rotary light dimmers can be fitted as alternatives. The cable for these switches usually runs down the wall within conduit within the plaster. A flush fitting wall box is sunk into the wall to accommodate the switch, or a surface-mounted box is used. Multi-switch units allow more than one light to be controlled from a single position.

In bathrooms and shower rooms, the switch must be a 'pull string' type. These switches can also be used for new light installations, as they can easily be screwed under a ceiling joist with minimal disturbance to the decorations. While there is a tendency to think that pull switches are only suitable for bathrooms, this limits the opportunities and should be avoided. For new lights positioned over work surfaces or even external lights, a pull switch can be mounted in any convenient position.

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Two Wiring Methods

There are two basic methods of wiring lights: by ceiling rose and by junction box.

The ceiling rose method involves making all connections at the ceiling rose. Although this removes the need for one junction box per lamp, it can be more challenging for the average DIY'er.

The junction box system, which is an older standard but still found in some installations, involves taking a cable to a series of junction boxes, one for each light fitting/switch. These junction boxes are typically located between the ceiling joists or under floorboards near the switch. Junction box connections are required for fluorescent lights and other fittings that do not use a ceiling rose.

Understanding domestic electric lighting circuits is essential for homeowners. With the right knowledge, you can ensure the safety and efficient operation of your lighting system.

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Frequently Asked Questions

1. How many lighting circuits should a house ideally have?
A house should ideally have at least two lighting circuits, each protected by a 5 amp fuse or 6 amp trip in the consumer unit.

2. How many lamps can a single 5/6 amp circuit cope with?
A single 5/6 amp circuit can handle up to twelve 100 watt lamps.

3. Can shaver units be connected to the lighting circuit?
Yes, shaver units can be connected to the lighting circuit. However, if installed in a bathroom or a room with a shower, the shaver unit must incorporate an isolating transformer.

4. What cable is used for lighting circuits?
The cable used in lighting circuits is a 1sq mm PVC twin core and earth rated for up to 12 amps. It consists of a red insulated core for live, a black insulated core for neutral, and a bare earth conductor.

5. What type of switch is required in bathrooms and shower rooms?
In bathrooms and shower rooms, the switch must be a 'pull string' type.

6. What are the two basic methods of wiring lights?
The two basic methods of wiring lights are by ceiling rose and by junction box.