Lighting cable switch and tripped fuse

[cpickering]

Recently done an attic conversion, and rerouted one of the light switches. The wall was plastered up by a plasterer and he took off the switch and taped up the ends red, black and earth. However two weeks after i try to connect the switch, and each time, its switched on the fuse box trips the rcd. I can not reset the RCd until i switch either the light off or the upstairs lighting circuit

I am wondering if the plumber has inadvertently stuck a nail through the cable when securing the plasterboards, and when the switch is switched on the black is earthing somewhere ? Can this be tested easily ? If the switch is in the off position no tripping occurs

 

[brown-nought]

1) You let a plumber use a hammer?
2) Check the wiring in the switch and ceiling rose. (RCD points in another direction) but check the black switch return isn’t run to the Neutral. (It should of course be marked by red sleeve or tape.
3) Use a multi-meter with the power off to check for continuity. Do 3 tests at the switch, all should give a positive continuity.
a. Red linked to Black at rose.
b. Red linked to Earth at rose.
c. Black linked to earth at rose.

4) Test for isolation (no continuity) between the wires with them not connected to anything at the rose. Either use :-
a. Using a continuity tester
b. An Insulation tester at up to the 500v setting.

 

[dw3101]

Do 3 tests at the switch, all should give a positive continuity.
a. Red linked to Black at rose.
b. Red linked to Earth at rose.
c. Black linked to earth at rose.

???

what do you mean by positive continuity???

David

 

[brown-nought]

Basically you are testing to ensure the cables are not broken. By joining two of the cables together you can test from the other end by putting one probe on each cable. The three tests ensure that all combinations of wires are used.

The isolation test then checks that none of the three wires are shorted together.

 

[delmel]

Recently done an attic conversion, and rerouted one of the light switches. The wall was plastered up by a plasterer and he took off the switch and taped up the ends red, black and earth. However two weeks after i try to connect the switch, and each time, its switched on the fuse box trips the rcd. I can not reset the RCd until i switch either the light off or the upstairs lighting circuit

I am wondering if the plumber has inadvertently stuck a nail through the cable when securing the plasterboards, and when the switch is switched on the black is earthing somewhere ? Can this be tested easily ? If the switch is in the off position no tripping occurs

Have you checked to make sure you have re-connected correctly. Note the lighting black is not a neutral, it is a switch wire and should be red, if you connect to the blacks this is the problem, one should go to the light the other to the reds.