Hi...been lurking here a while (as I've just bought my first flat), and now I need to ask a question... The bathroom extractor fan (timed) I bought has L/L1/N contacts. The wires I have to connect it with (in place from an old fan), are yellow/red/blue/earth.
I have searched and it *seems* that: L = Red L1 = Yellow N = Blue
I just wanted to double-check this was the correct arrangement. Also, the unit says it is "double-earthed" (or similar). Can I just snip the end of the earth wire off?
L will be permanent live and L1 will be switched live (i.e. only live when the bathroom light switch is on. Which of your red and yellow wires is which, you you need to determine with a volt-meter.
I assume that, being double insulated, the new fan doesn't require an earth and doesn't have an earth terminal. In case case, insulate the existing earth wire and tape it safely out of the way. Don't cut it off - it may be needed for your *next* fan!
OK take care with this since this since you are dealing with mains voltage here!
You will need a multimeter - if you want an easy to use one try something like order code N49AB from Maplin.
Assuming that you just have a dangling cable with the aformentioned three wires and earth to identify, I would suggest the following line of attack.
First turn off the lighting circuit at your consumer unit for the floor where the fan is.
Strip the insulation from the wires and spread them out so that you have easy access to each conductor.
Use the multimeter set to measure resistance (it may even have a continuity setting the bleeps when the resistance is low enough), and identify if any of the three seem to be connected. If none are, pull the light switch and try again. You should find with the switch on two of the wires are electrically connected. These will be L and L1 (live and switched live. The remaining wire will be Neutral.
Next you need to identify which live is which. Set you meter to read AC volts on a range 250V or higher. Pull the switch again so that the switch is off. Turn on the lighting circuit at the consumer unit. Connect the black lead of the meter to the neutral and see which of the others is live. That will be the permenent live.
Remember to turn off the circuit at the consumer unit again before touching or connecting up the wires.
John Rumm has given a detailed explanation but - in brief - use an AC voltmeter capable of measuring at least 250v (or a multi-meter with a suitable range) and measure the voltage between neutral (black) and each of the red and orange wires in turn. One of the wires (most likely red) will show ~240v all the time and will need to be connected to L. The other one will only show a voltage when the bathroom light switch is on, and will need to be connected to L1. [If it's a ceiling pull for on/pull for off type switch, you won't know for sure when it's on. But it doesn't really matter - just find which wire goes on and off with the switch]
Sorry - somehow I missed Johns reply the first time. Have just been at the new flat for a couple of days and last night managed to fit the extractor fan. It took about 2 hours (although the wiring was fairly straight-forward). It works fine now. Many thanks for all the help!
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