Doing some work on one of the lighting circuits, isolated via the RCD (rather than the MCB) by using the TEST button. All good, finished what I was doing, dropped all the other MCBs off, reset the RCD, then the individual MCBs and nothing working. Odd. Power to the top of the RCD, nothing at the bottom. With meter probes in the bottom of the RCD I found that by moving the switch very slowly I would get 240v at about half throw and then nothing at full throw (no feeling of innards clicking away or anything). Also when the RCD was (apparently) on the TEST button did nothing.
Eventually found that energising one of the MCBs and making sure there was a load on it caused the RCD to engage properly. Repeated the exercise (all MCBs off= RCD won't reset properly. no voltage and no TEST. Any MCB energised with a load on = RCD sets properly, TEST works properly). EDIT TEST also worked properly even if I switched off all the MCBs (so no load on the RCD)
Is this a feature of the model sir or a fault? CU is out of warranty alas but supplier (CED) still exists.
Eventually found that energising one of the MCBs and making sure there was a load on it caused the RCD to engage properly. Repeated the exercise (all MCBs off= RCD won't reset properly. no voltage and no TEST. Any MCB energised with a load on = RCD sets properly, TEST works properly). EDIT TEST also worked properly even if I switched off all the MCBs (so no load on the RCD)
Is this a feature of the model sir or a fault? CU is out of warranty alas but supplier (CED) still exists.