RCD question (for an Electrician maybe?) - Page 1
Forum section: electronics / general

author: aargee
author_rank: Frequent Contributor
timestamp: July 22, 2013, 01:57:11 am
content: In Australia, 240V domestic. Hager CD440T RCD.I had our RCD trip yesterday when a small switch mode power supply failed for a light. The SMPS blew a track off the PCB and is part of an earthed housing. The 20A circuit breaker for that house circuit did not trip.The RCD is an eight terminal type and protects three circuiits, two 20A power circuits and a 15A outlet in the garage. The lamp was on one of the 20A circuits. Now, yesterday resetting the RCD got the other 20A and 15A circuit back but nothing on the circuit that had the faulty lamp. There was just no 240V on that terminal of the RCD. 240V is fed to three terminals on the incoming side of the RCD via a bus bar and each circuit is then fed via a circuit breaker after the RCD.This morning, before calling an electrician, tripped the RCD using the test button, reset it again and all back to normal. Question is, why? Is there any other fuse/thermal protection inside a basic RCD? Could it have been a bit of crap on the terminals inside? I just can't explain the RCD behaviour.Thanks for any insights.- Rob.

author: David_AVD
author_rank: Super Contributor
timestamp: July 22, 2013, 02:13:09 am
content: Certainly sounds odd. I'd trip and reset it a few more times and replace if it plays up again.

author: Spunky
author_rank: Regular Contributor
timestamp: July 22, 2013, 03:20:06 am
content: There is no additional protection in an RCD, unless it's an RCBO (combined RCD and MCB). It sounds like scorched contacts, best replace it. Hager will be mid range, makes like Chana and Chint are cheap and work fine. Personally I'd always have 2 RCDs in a consumer unit operating split load, put your lights on one and ring mains on the other. I've yet to see a single 8 pole RCD though.

author: David_AVD
author_rank: Super Contributor
timestamp: July 22, 2013, 05:46:15 am
content: I had my house converted to a separate RCBO on every circuit a while ago. The workshop has always been that way. Much better for isolating faults and limiting the impact.

author: Spunky
author_rank: Regular Contributor
timestamp: July 23, 2013, 02:40:17 am
content: Yep, even better

author: Monkeh
author_rank: Super Contributor
timestamp: July 23, 2013, 03:00:42 am
content: Does sound like dirty contacts. I'd get it replaced, there's no easy way to tell if they've self-cleaned properly. Unless you've got a thermal camera to hand, anyway.It's a three-phase RCCB, which is why it has 8 terminals. Not something seen in the UK.

author: G7PSK
author_rank: Super Contributor
timestamp: July 23, 2013, 07:56:33 am
content: Used regularly on power plant.http://www.schneider-electric.co.uk/sites/uk/en/products-services/electrical-distribution/products-offer/low-voltage-protection/residual-current-device/id-rccb.page

author: SeanB
author_rank: Super Contributor
timestamp: July 23, 2013, 06:38:16 pm
content: The 3 phase vones can be very grumpy at times, I have had to change out a few that were a few years old and which would either not reset or which had dropped a phase. The regular single phase ones though do last well. At work i have added the 3 phase ones on a lot of the machinery, especially for those that are connected via a trailing cable and socket. Very expensive breakers though to buy, they are a lot more than buying 3 regular ones.