V
Vitesse
I got called to a domestic property today as the RCD 80amp 30ma kept tripping and wouldn't hold under load nor would the test button work. I removed the busbar to remove all circuits from the RCD and the test button works ok again, so it appeared the RCD was ok.
Tracked down the offending circuit causing the RCD to trip, in this case the ring final, which wasn't exactly difficult as it only happened when you plug something in. Carried out IR testing and found a neutral & earth short.
Plan was to split into the ring and IR test back to the CU but I spotted a odd looking FCU in the kitchen that didn't look like it was doing anything and it wasn't, apart from the face plate screw cutting through the neutral and then onto the earth that hadn't been sheathed properly. IR test again all ok, RCD tested fine. Job done. Really pleased sorted on opening just one box.
I understand the workings of an RCD with opposing magnetic fields cancelling each other out in normal operation, therefore the sensing coil picks up no magnetic field. I can't get my head around the test button though. I know it adds impedance across the neutral and live when pressed by introducing a resistor, which in normal operation is fine but I can't understand how in a fault scenario with no load, but earth leakage is occurring that it doesn't cause the RCD to trip?
Any ideas as it is bugging me?
Tony
Tracked down the offending circuit causing the RCD to trip, in this case the ring final, which wasn't exactly difficult as it only happened when you plug something in. Carried out IR testing and found a neutral & earth short.
Plan was to split into the ring and IR test back to the CU but I spotted a odd looking FCU in the kitchen that didn't look like it was doing anything and it wasn't, apart from the face plate screw cutting through the neutral and then onto the earth that hadn't been sheathed properly. IR test again all ok, RCD tested fine. Job done. Really pleased sorted on opening just one box.
I understand the workings of an RCD with opposing magnetic fields cancelling each other out in normal operation, therefore the sensing coil picks up no magnetic field. I can't get my head around the test button though. I know it adds impedance across the neutral and live when pressed by introducing a resistor, which in normal operation is fine but I can't understand how in a fault scenario with no load, but earth leakage is occurring that it doesn't cause the RCD to trip?
Any ideas as it is bugging me?
Tony