Apollo 13 like or something else?

[Newroad]

Evening All.

Firstly, apologies for any linguistic errors below - I hope you get what I am intending to describe.

Last night, the RCD on our Hager "Consumer Unit" tripped. This morning, I started by simply trying to reset the main trip switch, but it kept knocking out again after a few seconds.

After a few failures, I turned off all the individual "zones" (Water Heater, Upstairs Sockets, Downstairs Sockets, etc) then brought them up one by one. It appeared to be (and still probably was, but I'll say why there is some doubt later) one area of downstairs sockets which was the problem - each time I tried to bring up that zone, the main RCD tripped again.

I had some urgent stuff to do today, so I went and did that, and came back later.

When I tried again, I turned everything off that I knew to be in that zone (it could have been possible that I missed something) then brought them back one device at a time. Rather annoyingly, nothing tripped and everything is now running - I hate stuff that fails intermittently

Now whilst I'm very logical with debugging, I'm no electrical expert, so I'm wondering what the issue is/was, namely

1. An intermittent fault, or
2. It was a one off spike, but the restart is problematic, e.g. it can't restart the whole lot at once, a la Apollo 13 - https://www.youtube.com/watch?v=3SB_HHp8U9M, or
3. Something else?

Thoughts?

Regards, Newroad

[servodude]

1. An intermittent fault, or
2. It was a one off spike, but the restart is problematic, e.g. it can't restart the whole lot at once, a la Apollo 13 or
3. Something else?

Well it's definitely internittent

If you wanted to, you could try and see if you can throw the switch again (i.e. not waiting for another incident to cause it)
if it is to do with the loading on that ring at start up it should happen again (if it doesn't it's "something else"... gremlins... "environmental weirdness" ... could something have been damp?)

At which point it becomes a case of removing one thing at a time (as we know that adding them one at a time is not a problem)

If removing "something" causes it to work - try removing a different something instead to see if that also works
Stuff "looks" or behaves differently as it is being powered on both from a residual current perspective (especially with long cable runs) and absolute current (in-rush)
- it might just be that you are at the hairy edge of what your protection device can cope with when all the stuff is attached

[Newroad]

Thanks, Servodude.

Yes, that might be an option, especially if it happens again and can be brought up again.

It is Mrs Newroad's work area, amongst others, that appears to be affected, so if I do "force" a failure, I'd probably try that on a Friday night or Saturday morning - for, I hope, obvious reasons.

Regards, Newroad

[servodude]

Thanks, Servodude.

Yes, that might be an option, especially if it happens again and can be brought up again.

It is Mrs Newroad's work area, amongst others, that appears to be affected, so if I do "force" a failure, I'd probably try that on a Friday night or Saturday morning - for, I hope, obvious reasons.

Regards, Newroad

If the obvious reason is she doesn't do her arc welding at the weekend you might have your culprit

[Itsallaguess]

Now whilst I'm very logical with debugging, I'm no electrical expert, so I'm wondering what the issue is/was, namely

1. An intermittent fault, or
2. It was a one off spike, but the restart is problematic, e.g. it can't restart the whole lot at once, a la Apollo 13 - https://www.youtube.com/watch?v=3SB_HHp8U9M, or
3. Something else?

Generally speaking, it's pretty rare for protective-insulation on modern wiring to break down on domestic electrics, so my go-to priority-list for investigating stuff like this would be anything that -

• Heats using an element

• Is outside and might be getting wet, with particular attention given to outside lights and PIR devices

• Is inside and has water as part of it's operation

Given the time of year, things like tumble-dryers are often getting heavy use, which provide element-based heating.

Local-heating sources might be getting used in this cold weather - things like heated throws or warm-air blowers.

Recent snow is likely to be resting and melting on outside lights or fittings in a way that is not normally seen, where normal rain-based run-off might behave a little better than standing-snow that's slowly melting on electrical fittings or junction boxes outside.

Intermittent RCD trips like this are often difficult and frustrating to trace, but if you continue to see periodic trips, then isolating specific items with any of the above features for longer might help to focus in on anything giving earth-leakage issues. One of the most important questions to ask yourself with intermittent RCD trips, that will help with any investigation once you know the circuit in question, will be 'What was on or getting used when it tripped?'...

Finally though - don't rule out a fault with the circuit-based RCD protector itself. I'd certainly be looking for an end-device that's causing the problems here, as described above, but if you struggle with this issue over the longer term and can't find an end-circuit that's causing the problem, then it's not impossible for the circuit RCD to be the problem. Not likely, but not impossible...

Cheers,

Itsallaguess

[Urbandreamer]

Generally speaking, it's pretty rare for protective-insulation on modern wiring to break down on domestic electrics, so my go-to priority-list for investigating stuff like this would be anything that -

• Heats using an element

• Is outside and might be getting wet, with particular attention given to outside lights and PIR devices

• Is inside and has water as part of it's operation

....
Itsallaguess

This has ALWAYS been the cause of our RCD tripping.

The first, decades ago, was the oven element. No faults when cold, trip when used.
Later came the dehumidifier. Fine once dried out, but fault returned over time.
Most recently was the domestic iron (some 30 years old so didn't owe us anything).

Once you recognize the common factor it becomes a lot quicker to identify the root cause.

[DrFfybes]

There are 2 scenarios.....

Something plugged into the 'trippy' circuit that was not in use later or faulty later in - ie cold weather related or something that got damp. Do you have frost 'stat heaters in the garage or greenhouse, or a car battery conditioner, etc. Was the trip during daylight, could it have been a sensor light?

The other possibility is a faulty trip. In Exeter we had periodic board trips, this was a split board with 2 x RCDs, one for each half, although the main RCD would always trip - apparently the one nearest the supply always goes unless the supplementary ones are a LOT faster. I had 2 sparkys around, could never isolate or reproduce the problem. Eventually I decided to get some armoured cable run to the pond, and mentioned the problem to the chap who came to do it. He tested the board MCBs and RCDs, repeatedly, and on the 9th time one of the split board RCDs didn't trip. He repeated it and got it to fail again on attempt 20 or so.

He replaced it and all was fine afterwards.

The new board here is different, each circuit is on a combined MCB/RCD rather than the whole board.

Paul

[Newroad]

Hi All.

Thanks for the further replies.

Interestingly, the original trip happened in the early hours of the morning. There was, as far as I know, none of the usual things happening then which might put a higher load (e.g. heating water, using an iron, using an electric heater/kettle etc) happening then - we only noticed because the alarm panel started complaining about a loss of mains power.

Though I don't know every socket on that sub-circuit for certain, the part of the house is, in effect, is the converted garage and the adjacent section of the main house. There are no obvious opportunities for water to affect it - just a bunch of sockets at the standard height - and from memory, the electric cable drops down to them (rather than from the floor up).

The frost stat heater in the garage was a good shout - give the time of occurrence - but all the water heating etc is on a different circuit and I could bring that up separately without issue. Hence, unless it's a very weird configuration (possible but unlikely) I doubt it. If there is a next time though, I will check that more explicitly.

Regards, Newroad

[bungeejumper]

We had that type of intermittent failure many years ago. By using the process the OP has described, we eventually tracked it down to a metal table lamp fitting that had acquired an infinitesimally thin carbon track. On a good day, everything worked fine and we could reset the consumer unit. On a rainy Monday morning, not so much.

Mind you, it prompted me to check the condition of all our lights and wall sockets as well. And that was a little sobering. A convection heater that had been plugged into the socket for so long that it had become welded to the wall. A light switch, professonally installed, whose connection screws had loosened and whose front plate was starting to crack from the heat.

And more...

BJ

[Newroad]

Thanks, BJ.

I suppose the act of me unplugging and replugging everything on the sub-circuit in may have helped alleviate the problem in some way - until next time of course!

Regards, Newroad

[csearle]

I suppose the act of me unplugging and replugging everything on the sub-circuit in may have helped alleviate the problem in some way - until next time of course!

Firstly 98% of all RCD tripping is a result of water (or liquid) ingress*. All the other causes make up the remaining 2%. The 2% causes are over-sensitive RCDs/RCBOs, rodent damage, squashed cables, screws joining live wires to the fabric of the building, etc..

It is not always sufficient to turn off a trip switch in order to isolate the fault. Most trip switches only disconnect one of the live wires. The neutral usually remains connected, so if the leakage to Earth detected by the RCD is between neutral and Earth this will remain connected. So to isolate a final circuit properly it is necessary so to take out the neutral from the busbar as well as switching off the associated trip switch.

The leakage currents are cumulative, so the sum of all leakage could be just below the tripping threshold (usually 25mA) and a slight increase in leakage somewhere could suddenly cause the symptoms, but switching off one of several circuits (or unplugging stuff) could then stop the symptoms.

Fridges and freezers are devices that switch on periodically and can cause tripping when otherwise nothing is changing.

If the behaviour has suddenly started it is worth thinking hard about when the change happened and whether anything changed immediately prior to it. For example new appliances or a bit of DIY involving screwing something into a wall. Also a deluge and/or strong winds often cause ingress of water into outside lights (which are sometimes supplied from the sockets circuits via a fused connexion unit).

Happy hunting!

Chris
* Based on experience.

[Newroad]

Thanks, Chris.

Looks like I'm going to have to suck it and see (next time - assuming there is a next time) noting advice such as yours.

It is a strange one as there are few if any opportunities for water ingress that I am aware of in this case. However, the devil is always in the detail and as I have said above, I'm not currently in a position to audit all known connections on the apparent problematic sub-circuit.

As I write here, everything has stayed up today, so fingers crossed for the present. I can also put away the 10m extension cable and 8-gang extension lead!

Regards, Newroad

[Newroad]

Afternoon All.

Alas, it happened again last night, during the early hours of the morning. This time, even unplugging all the known sockets hasn't enabled it to remain on - it keeps tripping.

I've pinged a mate who's a sparky - hope he can fit me in.

It's really weird, as far as I can tell, nothing is on with respect to that sub-circuit - at least, I'm not noticing anything that's not working. And there was no rain and not any noticeable wind last night

Regards, Newroad

[Itsallaguess]

Alas, it happened again last night, during the early hours of the morning. This time, even unplugging all the known sockets hasn't enabled it to remain on - it keeps tripping.

I've pinged a mate who's a sparky - hope he can fit me in.

If you're wanting to try something whilst waiting for your mate to get back to you, and there's only adults in the house with no youngsters or pets running around, then it might be worth removing the socket face-plate screws on the troublesome circuit and pulling the socket faces away from the wall slightly, making sure that the power to the circuit is definitely off whilst doing so.

With the socket-fronts in a 'slightly off-wall' position, you can then try re-applying power to the circuit and see if it still continues tripping...

The thinking behind this is that if you're fairly sure there's no 'loads' on the circuit when it's still tripping, then any investigation might then turn to the underlying circuit infrastructure itself, where there may be an intermittent short to earth on either a live or neutral cable somewhere, and one of the most common areas for that to happen where it's a wiring issue and not a load issue that's causing such trips, is behind the socket faces themselves, with either cables being cramped too much after being pushed back into their sockets, or even long face-plate screws that can impinge onto cabling behind and to the sides of back-boxes sometimes.

You'd be surprised how many years a badly-cramped cable that's being pushed against an earthed bit of back-box can have it's insulation protecting it before it finally gives up the ghost and starts causing problems with intermittent trips like this...

It might ultimately be a faulty RCD that's causing this issue, but given you're probably not currently in a position to swap an RCD out at this stage, and if you're waiting for an electrician to come who might be able to look at that, then a fairly simple check of back-box wiring by dropping off socket face-plates is one of the simpler things you could maybe look to discount in your current position...

Cheers,

Itsallaguess

[Newroad]

Thanks, IAAG.

That makes sense - might give it a go, depending on how much time I have.

Regards, Newroad

[DrFfybes]

If you're wanting to try something whilst waiting for your mate to get back to you, and there's only adults in the house with no youngsters or pets running around, then it might be worth removing the socket face-plate screws on the troublesome circuit and pulling the socket faces away from the wall slightly, making sure that the power to the circuit is definitely off whilst doing so.

With the socket-fronts in a 'slightly off-wall' position, you can then try re-applying power to the circuit and see if it still continues tripping...

That has reminded me - we had a loose neutral where one wire had slid back out of the holder. I spotted it as it was on a spr for the garage door, but in a ring everything would still work, until it touched the metal back box

Paul