Wiring new lights

Wiring new lights

If you intend to make dramatic changes to an existing lighting system with lots of new lighting points and new switch positions, it’s probably better to install a whole new circuit than to try to adapt or extend an old circuit. This is also true if the existing lighting circuits are not earthed, although it is possible to install a single earth to a new lighting point – see below.

The theory and background of lighting circuits is outlined on page 52.

For an additional light on an existing circuit, it is usually best to organise the new wiring on the junction box system, the advantages being that only one twin and earth cable has to be run to the new light and that a shorter switch cable is required.

Linking into the circuit

There are three possible methods and the method which will suit will depend on the position of the new light relative to the existing circuit.

Trace this circuit by lifting floor boards on the floor above (or by going up into the loft space). Look for boards above existing lighting points which have obviously been lifted before – there should be a trap fixed with screws for easy access. Having found the circuit work out how many lights are already supplied and check that the new light (or lights) will not overload it.

Remember to turn off the mains before interfering with the existing wiring even when removing ceiling rose covers or junction box covers just to look at the wiring within.

Connecting to a loop-in ceiling rose Remove the cover of the selected ceiling rose and check whether it is the loop-in type. A loop- in ceiling rose will contain three (or if it’s last in the line two) cables with the conductors (nine in total) connected to a centre bank of terminals. Although the loop-in type of ceiling rose fitting is now often used whether or not the circuit is wired on the loop- in system, it is simple to detect the difference, a rose which is wired on the junction system will have just one incoming cable and several empty terminals.

By far the easiest loop-in rose to connect into is the last one in the circuit -. the one with just two cables coming into it. In roses already containing three cables there is little room in the terminals for the conductors of a further cable.

Connecting to an existing junction box Where the lighting circuit has no loop-in ceiling roses, the circuit will be wired on the junction box system. The first task is therefore to locate a junction box. If the new light is to be on the first floor of a two- storey house or the ground floor of a bungalow, all the junction boxes will be in the loft space and it will be easy to locate one suitable for connecting new cables -. again the emptiest and therefore easiest one is the last one.

Ajunction box mustbesecurelyfitted too batten placed between joists. An inserted box needstobeclosetothecjrcujtcablerun. For the mosteconomic use ofcable, a boxfora new light is best placed about midway between the new lightand the switch.

lfthenewcable isto betakenfrom a loop-in ceiling rose, it is easiest if the rose is the last in the line. Thiswill have spare terminalsfor connecting the live, neutral and earth conductors of the new cable, as shown.

If the newcable istaken from ajunction box,


The method of attaching the light fitting depends on its type but all connections should be made in a non-combustible enclosure.

Simple ceiling fittings These are either a ceiling rose with a pendant flex or a batten lampholder. Both these fittings have an integral backplate which contains the terminals and a screw-on cover.

Multi-outlet pendant fittings These are larger than the standard


ceiling rose sometimes with a separate terminal block mounted on the inside. All connections must be completed before the plate can be screwed to the ceiling.

Close-mounted fittings These are fixed direct to the ceiling with the circuit cable connected to a lampholder or terminal block in the light fitting. All these fittings should be supplied with an integral backing plate or be designed to fit directly on to a purpose-made pattress or a round conduit box – sometimes called a BESA box. In practice, a lot of close-mounted light fittings are sold without a backing plate and won’t easily fit on a box or pattress. For these the easiest solution is often a homemade backing plate—cut from a hardwood such as beech or mahogany with a neatly-cut cable hole.

Wall lights Most wall fittings are mounted on a recessed mounting box or an architrave box.

Where junction boxes are situated in the space between floors the search can be a thankless task as it isn’t always easy to guess where the boxes are. There are, however, two possible clues: first look immediately above the wall switches in the floor below; second look under the board running continuously along the landing.

When you locate a convenientjunction box check that it is on the lighting circuit and not a 3-terminal 30 amp ring circuit junction box – the size of cables is a good clue.

Connecting to an inserted junction box If the terminals of existing nearby junction boxes cannot accept an extra cable, the answer is to insert a new junction box into the circuit. This could then be the box for the new light or be an intermediate box.

Installing  Iightfittáng

All ceiling lightfittingsshould be screwed through the ceiling toa propersupport—a batten securely fixed between joists for instance. A hole is cut in the batten forthe cablesto pass through. Nailing the batten as shown will do fora fitting that isnttoo heavy but  heavy pendantwould need its batten supported on brackets screwed to the joists (see left). Aceiling -mounted pull -cord switch also needs a secure fixing.


If there is no existing earth conductor, one should be installed for the new light at least. Run a length of 15mm2 single core green/yellow pvc insulated cable from the junction box earth terminal back to the earth terminal in the consumer unit. This cable will not earth the rest of the existing lighting circuit, but it will provide an earth connection for the new light and switch. This is really only a contingency plan, if your lighting circuit is not earthed, consider renewing the whole circuit in twin and earth cable. Metal light fittings must always be earthed.


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