The dimmer is an electronic device which contains a semi-conductor, associated components and a TV suppressor. But unlike the old resistor dimmer, which consumed unwanted wattage and became very hot, the modern version does not use a significant amount of electricity and can be regarded as an energy saver.
These switches have been designed to replace any one-way lighting switch of the square-plate pattern, simply by removing the existing switch and fitting the dimmer in its place; this is connected to the same wiring and does not require any modification to the circuit.
If you are replacing the old round (tumbler) switch mounted on a wood block or plastic plate (pattress), it is necessary to replace the block or pattress with a standard flush-mounting box.
Warning In all cases follow the manufacturer’s instructions for fitting and always turn off the electricity at the mains before you start work.
Types of dimmer
The low-priced dimmer consists of a rotary action knob which reduces lighting from full brilliance down to off. This is adequate for most purposes, its one disadvantage being that the control has to be set each time the dimmer is switched on, since it has to be rotated through the full dimming operation to switch off the light.
There are many situations where it is more convenient to switch a dimmed light off and on without having to adjust the control; this can be achieved by fitting a combined dimmer and on-off switch. One type has a slide control for dimming; another has a milled-edge dial and a third a single push-on/pull-off control for switching.
A dimmer can be inserted in a two-way switching circuit to allow, for example, a landing light operated from both landing and hall to be dimmed as required. The dimmer switch can be fixed in any position, but for ease of wiring it is best installed near one of the two-way switches and preferably mounted on the same box, which would replace the existing one gang box (which takes a single switch).
To do this, remove the two-way switch and its box and fit a dual box, which in the case of a flush-mounted fitting will mean enlarging the recess in the plaster. A dual box is slightly larger than the ordinary two gang box (which takes two switches) used for double socket outlets and has two fixing lugs in the centre to take a fixing screw for each switch.
If the existing switch, in which a dimmer is to be incorporated, is a two gang unit controlling the hall and landing light, the two gang unit is retained. The dimmer, which is a one gang unit, must only be wired to control one of the lights.
Dimming two lights
Dimmer switches with a single knob incorporating push-on/pull-off action are made in two gang versions to control two different lights.
Dimming part lighting
A special combined dimmer/ on-off switch can be used to replace any existing two-gang switch unit to provide the facility for dimming some lighting in a room, while using the rest of the lighting at a fixed intensity. In a dining/ living room, for example, you can have a rise-andfall pendant over the dining table under dimmer control, while the centre light, wall lights or spotlights may be at fixed intensity, or vice versa.
There is a more expensive unit available which provides dimming facilities on two different sets of lighting and, like all the other dimmers, requires no alteration to the wiring when replacing a conventional switch, in this case a two gang switch.
Table lamp dimmer
Table or standard lamps may be put under dimmer control by fitting a lampholder adaptor. You simply remove the lamp, fit the dimmer in its place and insert the lamp in the dimmer lampholder. Intensity is controlled by a knob on the side of the dimmer.
Another version is available in the form of a plug adaptor. This is either connected to the flex of the portable lamp or has its own pins to connect with a socket outlet and has a socket of its own into which the lamp is connected.
Armchair or bedside dimming is possible with a portable dimmer switch, which is sold in either white or orange and has a black weighted base. The dimmer is controlled by rotating the top and slight downward pressure switches the light on or off. The control unit is connected by a flexible cord to a socket adaptor, into which the portable lamp is plugged.
The most recent type available is the touch dimmer, which is operated when a gentle touch on a small touch pad, fitted flush into the switch plate, operates the dimming and/or switching. These dimmers all fit standard square flush-mounted metal boxes.
One touch on the pad dims the light; repeated tapping varies the dimming until the desired level is reached. There are separate touch pads for changing the light level up and down and the unit has a memory which restores the light level after a power cut. These dimmers, which contain a fuse to protect the circuitry, must not be fitted into a two-way circuit.
Master touch dimmer
Another version of the touch dimmer enables dimming to be controlled from more than one switching position. For two-way switching, a master touch dimmer is fitted in place of a switch at one position and a slave dimmer at the second point or each point on an intermediate switching circuit. The master has a neon indicator.
Dimmer switch failure
Dimmers should be chosen and treated carefully because they contain delicate components. Never exceed the watts rating. Low-priced equipment with ratings of only 200 watts are satisfactory for simple light fittings; but if you are likely to install a multi-light fitting at a later date, it is better to fit a dimmer in the 400-500 watts range. This also applies to wall lights when there is a chance that more powerful replacement bulbs will be fitted later on.
If a dimmer is overloaded it will almost certainly fail. Dimmer failure is sometimes caused by failure of a light bulb when a surge of heavy current flows in the circuit and through the dimmer: this short circuit can exist long enough to destroy the semiconductor. To eliminate these risks, manufacturers are beginning to introduce small sand-filled cartridge fuses – similar to, but smaller than, a 13amp plug fuse – into their dimmer switches.