testing for the switch wire

[two_wheels]

I have what seems to be a common problem in this forum. I am installing a new ceiling rose and am stuck with 3 black and 3 red wires coming from the ceiling, not knowing which of the blacks is the switch wire.

I have bought a cheap electrical probe for £8 from B&Q which I hope to use to locate the switch wire. Can you tell me if the following procedure is correct:

There are 3 reds (all twisted together) and 3 blacks (all separate). With the mains power ON and the light switch set to ON I use the probe to connect from red to the 3 blacks, one black at a time. Hopefully only 1 black will register current and this is the switch wire.

Also, the ceiling rose has an earth terminal but there are no earth wires present - I assume this is ok?

Thanks.

 

[Adam_151]

No, the correct way is with the power off and the multimeter set to continuity or the lowest resistance range, connect to the red and black of each twin and earth in turn and flick the switch, you will find one of them (the switch wire) makes the meter chance from infinate resistance, to a very small resistance when the switch is flicked back and forth.

If your lighting circuit lacks an earth cable, you should use only class 2 fittings, and as this seems to suggust a fairly old installation, it'd be worth having an electrician conduct a piroidic inspection report on your wiring

 

[two_wheels]

Thanks.

Yes the house is 24 yrs old & we have just moved in. It also has an old style cartridge fuse box that I am keen to upgrade with an RCD, what's the going rate for this?

I realise that some other aspects of the wiring may also need upgrading, but gotta start planning the budget somewhere!

 

[Adam_151]

24 years old - it should have an earth in the cables, maybe they have been connected together and pushed into the void out the way?

replacing the cu, I'd budget £400 - £600, but there are many factors that affect this, and none of us on a forum can give a very reliable answer, and you're best bet would be to get three sparks round to quote, and go with the middle quote