lights not working

[timothyhall]

In the process of re-decorating the master bedroom, it was pointed out that the light switch is not flush with the wall, I tightened the two retaining screws, there was a pop sound and a small flash. The light would not turn on,  I replaced the switch with a working switch but still no working light. I tested the live wire expecting 240v but nothing – the breaker did not and has not tripped but there is no power to the circuit – any ideas?

 

[ProDave]

The "pop" would haver been when the screw tightened down pinching a cable, biting through the insulation and causing a short circuit.

Have you actually repaired that damage inside the switch box? with a bit of luch the damaged section will be near the end and you can fix it just by shortening the cable a bit.

Something somewhere has probably tripped. Do you have any fuses as well as circuit breakers?  Are all the other lights working except this one?
 

 

[Andy™]

or it could be the conductor blown apart, although that would have been obvious when trying to fit a new switch

 

[timothyhall]

hi,

i have disconnect all the wires, a continuity test suggests a short between the negative and earth.

I cant see any damage the the insulation on any of the wires !

The bathrooms on the second floor lights don't work, all the other lights on the second floor work, all lights on the third floor work. To my knowledge there are no fuses and the second/third floor light circuit has not tripped  

 

[ProDave]

There could well be a problem in another light switch where a cable may have blown. Time to get an electrician?  If you really want to try yourself, have a good look inside the switches of the other rooms that are not working.
 

 

[Andy™]

fault could also be in a room that is working

 

[Rob_the_rich]

1.Why do you think it is the "negative"?

2.What is the colour of the wire?

3.Is there only one cable in the switch with three wires including an earth? if more, how many?

 

[timothyhall]

1.Why do you think it is the "negative"?

it is black

2.What is the colour of the wire?

black

3.Is there only one cable in the switch with three wires including an earth? if more, how many?

there are 12 wires - three (red, black & earth) to one light then three (R, B & Earth) to the other light at the other end of the master bedroom, three wires spur off to the light switch for the en suite bathroom, the final three are the power in line.

 

[Andy™]

just because its black doesnt mean its neutral (not negative, that doesnt exist in AC)

 

[ProDave]

So is there any power on the "power in line"?
 

 

[timothyhall]

The black from the input feed is the one shorting to earth  

sorry, there is no power 

 

[Andy™]

you do know neutral & earth are linked together at various points, dont you?

 

[ProDave]

The black from the input feed is the one shorting to earth

sorry, there is no power

I don't know how you are measuring this "neutral shorting to earth" but unless you are disconnecting the neutral at the consumer unit, then of course it will appear that way.

If there is no power, the fault is in another switch box, junction box, fuse or who knows what. You need to widen your search. And as correctly noted earlier, the fault could well be in the back of another switch that appears to be working perfectly.
 

 

[timothyhall]

thanks for all the advice, i spent a bit of time taking each switch off ..... with 18 switches over the second and third floor it took some time, as usual it was the second to last switch that was working but proved to be the problem. replaced the switch now everything is working again 

thanks