Electrical

RCD trips instantly after smoke alarm replacement, even when I disconnect them?

Anonymous user 16/03/2024 - 2.41 PM

I have 2 wired smoke alarms that needed replacing so I bought 2 new ones to replace. When I dropped the 2 old ones, I noted that they appeared to be wired incorrectly (photo to follow). The 2 smoke alarms are connected together with a 3 core and earth, the 1st alarm is connected to a live and neutral from the lighting circuit. I replaced the old smoke alarms for new, and wired them up to match the old wiring (incorrect). This tripped the RCD instantly. So I wired up the new smoke alarms correctly this time, as per the instructions, but again, they tripped instantly. I disconnected both smoke alarms to see if the alarms were the issue, but the RCD still trips instantly (making me think there is a problem with the cable?). With a multi meter I checked for continuity between live and neutral, live and signal, neutral and signal... No continuity. I noticed that the earth in the 3 core cable is connected to the earth in the 2 core and earth (lighting circuit) that powers the alarms, i continuity checked the earth and it does have continuity with the black/blue neutral wires... (after reading up I think this is normal?) I'm now out of options and don't know what else to check? Currently, no smoke alarms are connected and the RCD still trips instantly. The smoke alarms share an RCD with the downstairs extension lights. Any suggestions / fixes would be much appreciated! The 2 things puzzling me are 1, why were the old alarms wired incorrectly to begin with? And 2, now that no alarms are connected, why is the RCD still tripping?