RCD Tripping

[Nickj]

How many cables are at the ceiling rose you have been working on? let me know and we can see how to proceed.

Hi Pete999,

Thanks for taking the time to respond again, I have checked the wiring at all roses, all except one are loop in, out, switch line. One just has line and neutral in with switch line. I'm guessing it's fed from a junction box as none of the other roses have been spurred from.

In the kitchen the line and neutral have been brought to the switch and I assume that was done to feed the power to the outside light.

All wiring seems in tact and correctly terminated. I cannot see how a line-earth fault has developed. Insulation tests are fine. It really has me scratching my head.

 

[Risteard]

If you are disconnecting the cpc at the DB try an IR test L/N to the earth bar in the DB, or leave the cpc connected.

Since the publication of the 17th Edition insulation resistance testing is required to be carried out with the cpc connected to the means of earthing. (That's not to say that some/many don't incorrectly test with disconnected cpcs though, of course.)

 

[Pete999]

Hi Pete999,

Thanks for taking the time to respond again, I have checked the wiring at all roses, all except one are loop in, out, switch line. One just has line and neutral in with switch line. I'm guessing it's fed from a junction box as none of the other roses have been spurred from.

In the kitchen the line and neutral have been brought to the switch and I assume that was done to feed the power to the outside light.

All wiring seems in tact and correctly terminated. I cannot see how a line-earth fault has developed. Insulation tests are fine. It really has me scratching my head.

Rose with just two cables is probably the last light on the circuit, have you dissed anything at the CU?

 

[Deleted member 9648]

If you are certain no sensitive loads are connected it is worth IR testing at 1000v. In the past I've used this to break down a fault which does not show up at 500v. Leaving it on the circuit for a minute or two is sometimes enough for the fault to suddenly show up.

 

[tony mc]

I dont think disconnecting the fan will make any difference if you previously got 20Meg on line to neutral it must of be switched off or putting 500volts has possibily fried it but i doubt you would of got a reading of 20meg.

As wirepuller has pointed out if all your tests show 20meg then if the RCD is in good working order it will hold.
The RCD should hold on anything above 7666 ohms so you are clearly missing something.


Let us know how you get on!

 

[Perryway-]

is it a split load rcd board?