I'm probably getting my two-ways and two-gangs in a twist, but can I wire more than one light fitting to a single switch, so that both lights go on when the switch is, er, onn-ed?
I've looked here and on the net and in my Collins Complete DIY Manual (2001) and in the Readers Digest Repair Manual (1972) but can't find quite what I'm looking for.
The target is to add a second light to an existing single-light/single-switch arrangement - which happens to be in my loft.
What I'm looking for is a diagram, preferably one for loop-in and one for junction-box wiring, as I have an interest in both.
You just connect the new light to the switched live and neutral of the old one in parallel. The required terminals are wherever the blue and brown wires from the pendant end up.
It is not affected by loop-in vs junction box vs old style singles. It is not affected by 2 or 3 way switching.
You need neither two-gang nor two-way for this: you want the second fitting to be "in parallel" with the first. This means that it gets its live, neutral, and earth feeds from the same place as the first light - or from the appropriate terminals of the first fitting.
So, in more detail: the very simplest way is to open up the rose which the first lamp is hanging from, and wire the cable which supplies the second fitting so that the earth wire (which you put a bit of green-and-yellow sleeving on) runs from the earth terminal, where all the other green-and-yellow sleeved wires run from; the black N wire from the terminal which the blue wire of the flex to the first bulb runs from, to which one or more existing black wires also run; and the L from the "switched live" terminal, which is the one the brown wire in the flex to the bulb runs from, and has only one incoming wire (which might be red, black-with-a-bit-of-red-sleeving-or-tape, or just black: this is the "switch return" wire, which carries the live back to the light fitting when the switch is "onn-ed"). (In an ordinary ceiling rose there'll be only two holes in the switched-live section, and no spare hole in the neutral section if it's a loop-in setup with an outgoing cable; it's quite OK to put two wires into one hole, making sure that both are firmly held by the one screw.)
If it's more convenient to connect into a junction box, the same principle applies: identify the terminals for earth (easy - all the green-n-yellow-sleeved wires run here), neutral (pretty easy, only black wires should be running here), and switched-live (single wire coming in, as for the loop-in case it may be red, black-with-red-identifying-thing, or black); wire the E, N, and L respectively cores of the cable supplying the second fitting into these terminals.
In both these cases, don't connect any wires from the new fitting to the fourth terminal, which will have a number of red cores going to it: that's the "permanent live" terminal, which feeds the switch and typically another cable running to further fittings. Since you want the new fitting to come on only when the switch is onn-ed, you've no need for this connection.
Third way is to fit a new junction box into the cable running to the existing fitting - assuming there's a little bit of slack in that cable, just cut into it, strip back conductors, sleeve the earth, and connect the three earths, neutrals, and lives into three separate terminals of the new junction box (each set of three wires coming from the two new ends you've just cut, and the feed to the second light).
All this assumes wiring colours in existing fittings are done conventionally. It's the switched-live which legitimatel varies - the three possibilities mentioned above are in increasing order of likelihood and decreasing order of best-practiceness. The switch-return wire will be red if the cable to the switch has two red cores - the "nicest" wire to use, but an extra cable type to buy for both the d-i-y'er and the professional. Much more common is to use the same red-n-black cable as the rest of the lighting circuit, where you wire the feed to the switch using the red core, as it's permanently live, and bring the switched live back up the black core. For the last 15+ years it's been considered Good Practice to identify this black core with a bit of red tape/sleeving, to show that although it's black it carries live when the switch is onn-ed; depending on the age of your wiring and how thorough the electrician/d-i-y'er was who worked on it, this identification may well be absent. (And just to confuse, it's not unknown for people to connect the switch with those colours swapped - black for permanent live and red for switch return. Not good practice, no, but not unknown, and doesn't affect function at all - electrons are colour-blind, after all ;-)
It's simpler than you think. All you need to do is take a feed from the wires supplying the existing lamp fitting (that is the pair actually feeding the lamp) to the new lamp. Plus the earth/cpc wire of course.
You don't wire into the switch, you want to wire into the ceiling rose of the existing light.
The switch only ever has two wires, one for live, one for switched live. When the switch is closed the switched live becomes live.
So wire your new light into the switched live and neutral of the existing rose. The switched live can *normally* be identified by a black cable with coloured sleeving (yellow?) slipped over the end. Neutral is easy.
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