home electrics

[MEANMACHINED]

how to wire a 3-way light switch

[New Forester]

Do you mean two-way? Two-way is where one light is worked by either of two switches. It really needs a diagram, but here goes: You need a two-way switch at either end. These can be recognised because they have three terminals on the switch instead of the two of a one-way switch (with me so far...?). Not counting earth blocks of course. The principle is that the first switch switches the power into one or other of two wires, which both connect the switches. The second switch then connects from one or other wire to the light. The circuit goes: - Live supply to first switch. - Two parallel wires to second switch. One or other of these will be live at all times. - Switched live from second switch to light. - Wire from light to supply neutral. In practice, you usually wire from each switch to the ceiling rose, and from the lighting circuit also to the ceiling rose. You may need an extra connector block inside the rose, in addition to the ones it has already. If you work this out, it means you end up needing three wires (plus earth) between the light and each switch. Normally one uses triple-and-earth cable for this, which has red, blue and yellow wires plus an uninsulated earth. Use red for the live supply or switched live, and the other two for live 1 and live 2. It is also possible to work one light from more than two switches -- this works the same whatever the number of switches, and is good, for example, for stairwells in large buildings. For this you also need four-way switches (with four terminals). These connect two parallel wires straight or crossed at each switch. Ask another question for more explanation of that.