:( is my lighting earth earthed or not?? :(

[vice]

Hi. I'm installing some metal light switches. One box is plastic and doesn't have it's earth connected so I double checked that it's other end was connected . It wasn't so I've connected it into my lighting circuit in the roof. Sounds fine eh.

But.. if I use an multitester to check the resistance between this earth at the switch and the face of another upstairs lightswitch OR the cold water pipe in the bathroom, both give a fluctuating reading of around 1500k ohms. I did this other lightswtich the other day at it and a neighbour already had earthed connected in their boxes. Resistance between them was zero. So is my other box earthed? Multimeter gives a 1 if no connection at all, i.e. infinite. but such a high resistance just seems mad!

They're connected somehow, but could be via a big edam or something. Any ideas? Could I connect the earth to the neutral to check all is working? Where to turn???? HELP !

 

[riveralt]

If you have metal light switches then they have to be earthed themselves- normally from the cable that supplies the live and switched live - they normally have an earth terminal on the rear of the switch. Whether you then have/need a fly lead to the rear of the back box is another debate.

 

[1john]

disconnect and join live to earth at the consumer unit and test between live and earth at each point, you need a low reading of a few ohms, on most small domestic lighting circuits I cannot recal having a circuit which read more that say 2 ohms, this is with a proper continuity tester, readings with a multi meter will not be as true and you will acheive a higher reading.

 

[Spark123]

Best advice is to call in an electrician - the wires in the back of a switch are more likely to be switch wires and will potentially give you a shock if you start cross connecting them!

 

[riveralt]

disconnect and join live to earth at the consumer unit and test between live and earth at each point, you need a low reading of a few ohms, on most small domestic lighting circuits I cannot recal having a circuit which read more that say 2 ohms, this is with a proper continuity tester, readings with a multi meter will not be as true and you will acheive a higher reading.

Given what he has said so far, not sure he should be going near the CU

 

[vice]

sorry. Yes,, of course a connection won't trip anything since they are switch wires not a live and neutral. The resistance is very odd though. Being the size it is it seems to be connected but massively inhibited. Stumped.

 

[riveralt]

sorry. Yes,, of course a connection won't trip anything since they are switch wires not a live and neutral. The resistance is very odd though. Being the size it is it seems to be connected but massively inhibited. Stumped.

I'm very sorry but it is impossible to help you because nothing you have said so far makes any sense.

 

[vice]

Doesn't make sense to me either.

I've connected up an earth in a light that previously wasn't connected, to change a plastic switch to a metal one.

I used the earth present in the switching wire already in use, the earth not being connected at either end previously.

I get a connection to the earth circuit indicated with a multimeter but with a massive resistance (ok AC- impedance). This is the resistance to both another switch and to a water pipe.

So I don't know if I truely have an earth since the resistance should be tiny, not massive.

 

[1john]

earth may have been disconnected as it has a fault on it. best install the plastic switch again until it is checked.

 

[riveralt]

First of all did the previous plastic switch work?
Did the switch turn on a pendant ceiling light?
Does the ceiling light have a ceiling rose?

 

[vice]

the plastic switch connects up to a rose in the loft to which 4 halogen spotlights are connected. The rose is connected off the lighting circuit in the loft.
The switch worked fine. All other upstairs lights are spots, some low voltage some main. None requiring an earth so this is the first one connected to the circuit.

 

[riveralt]

the plastic switch connects up to a rose in the loft to which 4 halogen spotlights are connected. The rose is connected off the lighting circuit in the loft.
The switch worked fine. All other upstairs lights are spots, some low voltage some main. None requiring an earth so this is the first one connected to the circuit.

Just focus on what this switch turns on....

If, as you say for this switch you have a ceiling rose and that four spots run from it - then are there earth wires connected at the ceiling rose and how many?

 

[vice]

there an no earths connected. The live and return of the four spots are wired into 2 of the rose terminals, the returns connected with the circuit and one of the terminal connecting the live in and the switching across to the live of the lights.

 

[1john]

if no earths are connected how did you expect to get a reading??

 

[riveralt]

Based on what you say - that this light switch operates four spotlights in the loft and that there is no earth at the ceiling rose that controls these spots or that leads from another earthed ceiling rose - then you cannot have a metal switch - most manufacturers instructions (those that came with the switch) will state this.

I would suggest that you return to the plastic switch and have an electrician check out your lighting circuit.