RCD socket

Can anyone suggest what might stop an RCD socket resetting with nothing plugged into it?

I had the power off earlier today and might have disturbed the wiring near the distribution board but I can't see how anything upstream of the RCD could affect it.

I have a feeling this happened once before - a fail for no obvious reason and I had to replace the socket.

Neil

Insect activity or moisture penetration perhaps

Brian

Hi Neil,
I came across an RCD spur box ((Now they seem to call them connection points.) that came with a second hand stair lift I bought for my mother that would drop out if there was a power interruption on the input. I did not know if it was a special that was fitted as some kind of safety feature on stir lifts. I thought it was more of a negative feature as my mother then had to walk up the stairs to reset it. I did think of replacing it with one that did not need reseting after a power loss. (But I never got round to it.)

Les.

It's that pesky workshop gremlin again..

George.

I know that there are two distinct types of RCD socket available, one type will stay set and the other needs to be reset every time it is used. I'm sure one of the electrical guru's will explain the difference.

All my RCDs have to be reset if power is lost. I thought that this was a safety feature, rather like a NVR switch.

Howard

I have two plug in RCD's both trip when I switch the power off & I have to reset when I re-plug them in & switch power on.

George.

That usually indicates a neutral to earth fault. When in the game we regularly had to change faulty ones. As you say anything before the SKT should not effect it. Do you have a meggar to check the insulation readings of the circuit feeding it. Still should not do that though. Maybe a bit of logic & assumption on my behalf. Assuming this is in your workshop or wherever. Is the house Dis board protected by a ELCB. If it is & not tripped then it would indicate that the SKT has failed.

Steve.

have you checked to see if you have a live and neutral at the RCD socket either one missing could result in a no reset.

Gren

Thanks for the suggestion Gren, it's possible but all the other sockets in the ring are functioning normally.

I am sure this is the second one I've fitted here, it is what we use for pressure washers etc. but normally it also has a freezer plugged in to it...

I think it only ever trips on the rare occasions when I test it. I suppose it's possible the power cut tripped it and it got stuck mechanically (I imagine they are designed to fail safe).

Neil

Is it the type that switches off if the power fails? If it is it suggests a loose connection between it and the incomimg supply, A situation I have found to be not uncommon today, as noone seems to tighten screws in electrical fittings tight enough, and some of the terminals, especially those on MCB's etc are notoriously difficult to get a proper clamping effect on the cable. If it is not the type that cuts out when the mains goes off, it suggests a faulty unit. If you feel confident doing it, Isolate the consumer unit by whatever means is at your disposal (I remove the cut out fuse) and check all the screws in the CU and downstream for tightness and proper cable insertion. You might be surprised at what you find!

Could also be caused by Voltage spikes from the mains, especially if the electronics in the sockethas earthed capacitive filters fitted! Unfortunately neither these or MCB's are designed to fail safe!!

Edited By Phil Whitley on 03/05/2020 19:13:33

Edited By Phil Whitley on 03/05/2020 19:14:49

Re Phil Whitley’s comment about removing the cut out fuse.

This is not something that individuals should do. It belongs to the local electrical network operator and should only be removed by someone authorised by them, following appropriate training and knowledge and using the correct PPE.

Neil, I work in a business that tests RCD's and RCBO's by the many thousands each year, both new and used, and regularly find units that will not set under power due to internal failure of the monitoring circuitry. They are not repairable and all that you can do is dump them. We have a failure rate of about one in a hundred that fail in this manner - worryingly we also find about 2% that do not trip under severe fault currents - that is why it is essential to regularly test them using the test button which injects a small fault current into the circuit. As mentioned we also test new units which also occasionally fail.

Steve

Thanks Steve,

FWIW folks I installed the ring main this socket is on, and it has been tested and OK'd by a professional.

Also our main fuses (standard and Economy 7) are accompanied by big isolation switches, not to mention the ones on the distribution board.

I've booked half an hour at 3:00pm to switch everything off and fit a new junction box (looks like flood water got into the old one under the floorboards). but I'll have to order a new RCD socket.

Neil

I knew I shouldnt have said it! HoweverTO BE SAFE, it is essential to isolate the supply. I cannot imagine what " appropriate training, knowledge and PPE" it takes to remove a full insulated fuse from its fully insulated holder, but as an electrical engineer of some 50 years experience, I have done it countless times. The problems I have found, is that the loose connections and substandard equipment only seem to be present in recent installations, which were installed by people who are supposed to be in possesion of the "appropriate training, knowlede, and PPE".

Neil, If you can isolate before the Dis board, check the connections in the dis board for tightness, including the main incoming supply cables. On the MCB's it is very easy on some models to get the screws tight, whilst not effectively clamping the cables, give them all a good pull to see if any come out. You might be surprised!

+1 on Steve Skelton 1's post!

Phil

A friend was involved in planned maintenance and added checking RCD’s with the test button on a layout that had been running for a few years, every spot welding controller had an RCD so in a car factory there are many hundreds of these, a high percentage refused to trip when tested. I accept that regular checking is specified by the manufacturer but this is time consuming on a large installation and PM often suffers when other tasks trump it. In theory we were supposed to do a safety buy off every year which involved checking every safety device functions correctly and the safety PLC checksum matched the buy off reference. It is surprising what you find when you go and look for it. Although the regulations now specify RCD protection I wonder just how many will work when they need to, the flip side is the nuisance tripping from equipment that is a bit leaky. The maintenance supervision moved into a new office and found that when they turned all the computer monitors on the trip would operate, the 5 monitors were all CRT type in those days. The office had its own consumer unit so I had a nose and noticed a 10mA trip was feeding the office ring and the accumulated leakage from the 5 monitors was too much for a 10mA trip. They got it changed for a 30mA and it was happy days.

Mike

Edited By Mike Poole on 04/05/2020 22:43:02