Low-voltage lighting is supplied with power at 12 volts from a transformer. This means that power consumption is greatly reduced compared with mains lighting at 240 volts. The other advantage is that the fittings use small halogen bulbs, which give an intense white light that is perfect for creating dramatic lighting effects or highlighting features of the room. Halogen bulbs are more expensive than standard light bulbs, but have a relatively long life provided that they are not repeatedly switched on and off (so, in other words, you may have to get used to sleeping with the lights on!).
Choosing Fittings
There are three main types of low-voltage light fitting. The first is designed as a direct replacement for an existing light fitting. It consists of a round, surface-mounted base unit, which contains the transformer, and a circular plate, a rigid bar or a twin-wire track on which the individual light fittings are mounted. The halogen bulbs are usually rated at 20 watts.
The second type consists of a separate transformer, which has to be concealed in the ceiling void, and a number of individual low-voltage fittings (usually recessed downlighters), which are connected to the transformer by lengths of cable. The transformer wattage is matched to the total wattage of the lamps it is supplying. These may be rated at 20 or 50 watts.
The third type consists of individual light fittings (again, usually downlighters), each with its own slimline transformer. These fittings are wired in series, and each transformer is designed so it can be passed up into the ceiling void through the hole cut for the fitting. Access is needed to the ceiling void to install the cable run from light to light. Again, 20- or 50-watt bulbs are usually fitted.
Surface-Mounted Fittings
Turn off the power. If you are replacing an existing ceiling rose or light fitting, site the new fitting so the transformer unit is mounted over the old light position. The existing wiring can then be connected directly to the transformer terminals. If the fitting is to be installed in a new position, run a spur cable to it, via access from the ceiling cavity, from the lighting circuit, to a new four-terminal junction box wired into the circuit. You can then connect a switch cable to the junction box to provide separate control of the new light.
Disconnect and remove the existing ceiling rose or light fitting. If only one cable is present, connect it to the transformer input terminals. The transformer does not need earthing, so cut off the cable earth core flush with the cable sheath, or wrap it in PVC insulating tape for future re-use if the light fitting is changed again.
If two or three cables are present, connect them to a strip of four terminal blocks. Then connect one end of a short length of cable to the switch return and neutral terminal blocks in the strip, and the other end to the transformer input terminals. Pull the bare earth core out of the cable sheath before connecting this cable up; it is not needed.
Screw the transformer unit to the ceiling – directly to a joist if possible, or with cavity fixings otherwise. If it has a track or support wires, attach the mounting brackets to the ceiling and fit the bar or wires into them. Position the light fittings as required and restore the power supply.
Single-Transformer Systems
Turn off the power and gain access to the ceiling void above where the lights are to be installed. Run the power supply to the transformer as a spur from a new four-terminal junction box into which the new switch cable is also wired.
Cut a hole in the ceiling at each light position, using a hole saw. Clip the fitting into the hole. Screw the transformer to the side of a joist and connect the supply cable to its input terminals. Run a feed cable from the transformer output terminals to each light position and connect each feed cable to its terminal block. Clip the cable to the side of the nearest joist. Run cable from the junction box to the position of the new light switch. Mount this and connect the cable to it. Restore the power supply and test the new lights.
Multi-Transformer Systems
This is similar in wiring terms to the single transformer system described opposite, except that every light has its own transformer in the ceiling. The circuit cable runs from one light position to the next, emerging as a loop through each ceiling hole. Cut the cable at each light position and connect the cores to the transformer terminals. Then plug the light fitting directly into the output terminals. Insert the transformer into the ceiling void through the ceiling hole, and clip the light fitting into place. Repeat for the other fittings, then restore the power supply and test the lights.
