WARNING ELECTRICITY CAN SERIOUSLY INJURE OR KILL.
IF YOU AREN'T SURE WHAT YOU'RE DOING, CALL AN ELECTRICIAN
This is only an illustration of how it should work, it is NOT a guide intended to enable you to carry out the work
Have you taken your light down?
Have you forgotten where all the wires go? You're not on your own; it happens a lot. If you're in this predicament here's a description of how it all works, and what the electrician will be doing when he restores your lighting. Most of the time when people get confused it is because they don't look at what they are disconnecting and don't take note of what goes where. This situation is compounded by a method called "the 3 plate system" which means there are more wires in the ceiling rose than they expected. If we look first how the circuit is laid out from the fuseboard and around the house, we can see that the cable comes from the fuseboard to the first light, then out again to the next light, and again to the next one and so on.
In reality these cables have 3 wires, or cores in them. One is the live conductor (red or brown), another is the neutral (black or blue) and the other is bare copper, the earth conductor. For the purpose of this illustration we will ignore the earth conductor except to say that they should all be connected together wherever they meet.
You can see too that from each light there is a cable going to a switch.
So, if we were to take down one of these lights, for instance the one circled in figure 1 above "X" we would have three cables going into the light, each one having two wires (discounting the bare earth wires don't forget) and it would look something like the drawing figure 2.
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This shows the cable "A" coming from the fusebox, cable "B" going off to the next light and cable "C" going to the switch. You will notice that the cable to the switch has two brown coloured conductors whilst the others have one brown and one blue. This is because when the light is switched on, both these conductors to the switch are LIVE. This is often misleading though, because, you may find that the cable coming to the switch has a brown and a blue (or a red and a black in old colours) just like the others. In this case there should be some indication on the blue cable that it is the live coming back from the switch (the switch wire).
This is usually a piece of brown or red insulating tape attached to it or a similarly coloured plastic sleeve inserted over it.
So; referring to figure 1 you can see that there are 3 connection blocks where the wires are joined. This is a true representation of a ceiling rose. The centre connection (2) with three screws in it, may be labelled "loop" and you can see that the live conductor from each cable is connected to it. These are the live in (from cable a), the live out and live down to the switch, which in figure 2 is in the off position.
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You can see too that the neutral (blue) from cables A&B are connected together with the blue wire from the bulb. In this position (switched off) you can see that the live voltage comes into the ceiling rose, and is taken down to the switch (position 4) via the brown conductor in cable "C", but because the switch is "off" position 4b is still not live. It is important to note that even though the light is switched off, there is a potentially dangerous voltage present in the ceiling rose at connection 2. If you disconnect those neutrals at connection 3, there may be danger there too unless the whole circuit is isolated like it should be!! If we now turn the switch to the "on" position we can see that 4b, and therefore terminal 1 will become live. This puts a voltage to the light bulb, and current flows through it, returning through the neutral and the light is illuminated.