by ericmark »
Tue Jan 08, 2019 4:18 pm
A multi-meter is not a magic wand. It is just at tool. With power off a bell and battery could be used to find out which cable goes to switch, in the same way as with a buzzer or ohm range on multi-meter.
I was really surprised when I went to do an 'A' level Physics, I wanted maths but if I did three it was £10 and just one over £100 so did three.
They provided the class with multi-meters, and the students were to measure volts and amps, and they managed to rupture 15 fuses in multi-meters. I thought the 'A' was for advanced?
And this is the problem as an electrician is seems easy, but clearly even advanced students could not follow what I thought were fool proof instructions, with a 12 volt power supply no problem, with 230 volt ac that is a different thing.
The forth cable can't help much, but first three likely one goes to the switch, and with the power off, and I mean total off at the consumer unit, then it is possible to put a meter/bell or other device across the brown and blue wires to test continuity and flick the light switch on/off until the switch wires are identified.
But forget to turn off power and then big bang is possible.
I worked out a truth table to enable testing without a meter, however make a mistake then again big bang, ionisation of the atmosphere is extremely dangerous and when I tried to relate how to use a truth table on here, I was banned for a time, as it is so easy to make a mistake.