Circuit breaker trip puzzle

If the whole house tripped out you've probably got one RCD for everything. This works by looking for an imbalance in current flow between the line and neutral - if everything is ok the current in each of these will be identical. If, however, either of those conductors has a fault to earth - doesn't have to be a short circuit - the device will trip. And it can happen with a single pole switched device even when it's off.

Mineral insulated heating elements like immersions and some oven elements are notorious for this sort of fault - you get a slight leakage to earth, but it still works ok. And it's unlikely to be the same on both legs so upsets the RCD which trips.

These days most recommend a split load CU where only some circuits are RCD protected, and things like the immersion and cooker - which are hard wired so no safety implication there - are fed from the non RCD side.

--
*Many hamsters only blink one eye at a time *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

The immersion heater switch is normally a double pole type, so if it's switched off, the heater element is completely isolated anyway, so cannot be responsible for for its feed MCB detecting leakage. When you say that your house had lost all power, was the actual consumer unit breaker tripped, as well as the immersion heater MCB, leading you to believe that an immersion heater failure had tripped both ?

Arfa

Tripped MCB or RCCD/ELCB device?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Do you have an example of a modern distribution panel and it's circuits for your UK residential wiring? This kind of fascinates me.

Thanks for those prompt and helpful replies. I'm responding to the requests for more info:

The unit is a 'Crabtree', and carries a label '8A/30mA'.

It has two sections:

CIRCUIT BREAKERS:

-----------------

1. Upstairs lights: 2 shaver-sockets in bathrooms; outside security light (from loft extension)

1. Downstairs lights: hall, kitchen ceiling & under cupboard, downstairs toilet (and fan), cupboard under stairs (and alarm)

2. Downstairs lights: lounge, dining room

1. Transformer by board (This is an add-on of my own, as part of a gadget to detect when the front door bell was pressed, to buzz a garden extension. Not a possible culprit IMO.)

2. Spare

RCD PROTECTED CIRCUITS:

-----------------------

1. Immersion heater. (This is the one that tripped.)

1. Sockets (radial): My office. Too many items to list here.

2. Sockets (ring): Downstairs except kitchen (5); Garage (1); Upstairs except main bedroom (6)

1. Sockets (ring): Main bedroom including spurs (1): Hall (1); Kitchen (6), Utility (3), upstairs bedroom

2. Cooker and 1 socket by cooker switch.

I also have two other RCD units

- In garage mains socket, protecting garden and workshop circuits

- In lounge mains socket, protecting garden pond submersed pump

After the failure I thought *all* power was lost. But now I can't be

100% sure whether I had the lights on, and I don't recall checking them. Certainly things like fridge, microwave, etc were off.

The only switch I reset in the Crabtree unit was the RCD one controlling the immersion heater.

I haven't unscrewed the immersion heater wall switch yet, so can't confirm whether it's single or double pole. But doesn't the fact that this RCD was tripped mean that it *must* be single pole, with a leak?

Hope this helps further diagnosis.

--
Terry, West Sussex, UK

Probably just that that RCD trip is more sensitive to unbalanced inductive load on another circuit, usually the motor of a washing machine but theoretically could be due to a neighbour using an arc welder, anything else very inductive, distant lightening strike etc. If definitely no problem with the immersion wiring then change the RCD.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Because of nuisance tripping this would normally go on the non RCD side.

Likewise this - but remove the socket.

The only way everything could go off with a split load CU is if the main fuse blows. That's the 'company' one before the meter.

You mean the RCD controlling that side of the board - not the MCB for the immersion?

Could be anything on that side of the CU.

--
*No I haven't stolen it , I'm just a shit driver*

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

All agreed. If it was only the MCB for the immersion circuit that had tripped, this could not affect all the ring and radial power circuits ( and possibly the lights too ! ) unless there is something seriously wrong with the way it's all wired. You must be talking main RCD trip for that side, as Dave says ? As far as the immersion switch goes, it could indicate single pole and a leak for the MCB on that circuit tripping, but in order for all the other stuff to have gone out as well, there must have been something else tripped on the feed to that side's fuse bus.

Arfa

Is this the SB6000 series by any chance, or at least that series/vintage? (20 years old or more I'd think now!) There should be a label somewhere on the fascia.

If so, these are known to get 'twitchy' as they age, the breakers trip for no apparent reason and the only cure is replacement. However, I'm not sure the individual breakers are available now, you may have to replace the whole distribution box if it becomes troublesome- like I did!

If the problem reoccurs regularly it would be wise to consult an electrician and get a quote. If it's just the immersion heater circuit though, you may choose to just live with the minor inconvenience if it isn't regularly used and spare breakers can't be sourced- changing the whole distribution box isn't cheap!

Morse

Thanks for the follow-ups. I'm going to have to do some more careful reading, maybe starting here

as I don't really understand the basics, and hence some of the advice given. Meanwhile, beginning to regret switching from my old fuse-based unit a year or so ago!

The Crabtree is a modern modular unit, but so far I've not found its spec. I'll do so as soon as possible and report back.

--
Terry, West Sussex, UK

on

for

sure

electrician

may

used

Is the local supply into your house by overhead wire or underground feed.? Do neighbours on the same phase (their lights go off with yours, about every

1 in 3 houses if there is a local sub-station/transformer problem/power cut) have similar problems ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I've also taken a photo and labeled it as per my previous post.

(BTW, MCB #5 on the RCD side is disconnected.)

Note that I realise that the RCD controls electricity to all the MCBs on the RCD side of the unit (not just the immersion heater). But I think I was correct in my recollection that the only switch I reset in the Crabtree unit was the RCD one.

--
Terry, West Sussex, UK

Underground feed.

Yes. By coincidence, the following day there was a 1 minute general power cut, as I later confirmed with my immediate neighbour.

--
Terry, West Sussex, UK

"Terry Pinnell" wrote in message news: snipped-for-privacy@4ax.com...

It could be that you had a brief general (street-level) outage, and that when it came back on, for whatever reason, it tripped out the immersion heater MCB. You would have expected that for that to happen, the immersion switch would have needed to be on, but odd things like this can happen, particularly if it is just a single pole switch. MCBs can be sensitive to the strangest (non) fault conditions. If the consumer unit was replaced recently by a reputable certified electrician, then there's a good chance that there is nothing wrong with the wiring to it. A decent electrician would probably have checked the external circuits for leakage whilst he was doing the job. I think if I was in your position, I would probably wait and see if there were any more 'events', but if you would prefer total peace of mind, I wouldn't have expected it to cost *too* much to get an electrician in (probably not the original guy, just in case, unless you know him and his work well) to just check over the immersion circuit in particular for leakage. I honestly don't think that he would find anything, because if your recollection is correct, and you had a total power outage, but the only thing tripped was the immersion MCB, I can't see any way that this could be for any other reason than the actual feed to your house dropping out. The fact that you had a 'known' outage the next day which was due to the feed dropping out, might well suggest that the electricity company were either doing some work on the loop that feeds you, where they often 're-route' temporarily to kill the section that they are working on, whilst keeping the subscribers live, or else that they were having some tripping or equipment issues of their own. When these big old company breakers remake, they can generate some pretty big spikes. I have a national grid switching station not far from me, and when they have any switchover or breaker issues, it lights up the sky like lightning !!

Arfa

Was the work done by a qualified electrician? It just seems strange to me that the immersion is on the RCD side. And since you said it replaced a fuse based unit was the house re-wired at the same time?

If it's a current Starbreaker unit I've fitted several including my own and they've been fine.

--
*Tell me to 'stuff it' - I'm a taxidermist.

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

Many thanks, appreciate that thorough advice. It certainly would be reassuring to believe that it *was* caused by a very brief 'brown-out' or whatever you call these things. It could fit the facts too. On my way out to the garage, where the CU is located (cursing a bit - I was in the middle of authoring a DVD on my PC when it happened), I saw that the cooker clock was still on. Now, a few months ago, after a bit of telephone advice from the electrician, I disconnected the cooker from the CU's control. This was because I wanted the facility to use its wall socket for emergencies, prompted by an exciting event when the old washing machine packed up with my laundry still inside. So, seeing the clock still on, and the immersion heater trip switch tripped, I concluded that it was a fault within my house, and posted as I did. But as you say, it might have been a wide outage, at most a few seconds long (rather than about 2 minutes like the one the following day), and (again unlike the one the following day) it could have caused that odd side effect.

One thing I *have* decided though is to capitalise on that cooker socket and connect my fridge and freezer to it during our fortnight's holiday ;-)

--
Terry, West Sussex, UK

Yep, albeit fairly young.

Is that abnormal? Why? Should I get him to switch it over to the other side?

No. And my 'extra' wiring (mostly done about 12 years ago) got the predictable negative reaction ;-)

Yes, it is a Starbreaker, as you can see from the photo I posted earlier.

--
Terry, West Sussex, UK

This puzzle now has another twist. I decided to do some methodical leakage tests. My intention was to introduce a leakage from the live connection of the circuit under test to a convenient earth, and observe what tripped. That would at least confirm that I understood what behaviour I was *supposed* to get from my Crabtree StarBreaker CU. I used a couple of robust 15k resistors in parallel, theoretically giving me a leakage around 32 mA (in my UK 240 V circuits).

I decided to start with an unimportant circuit, which also had an extra RCD unit over and above the main CU. This is a double socket RCD in the garage, fed from #3 on the Main Switch (non-RCD) side of the CU. As expected, momentarily connecting this leakage current immediately tripped the garage RCD. However, to my surprise, maybe 1-2 seconds later (with the leakage removed), the *main* switch on the CU was tripped. So my PC and various household devices and clocks went down despite my cunning plan ;-)

I'd not have expected this to happen, so could someone offer a possible explanation please? Does it offer more insight into the odd behaviour already reported?

In case it helps, the electrician's scrawled installation notes record trip times of 18/19 ms for all the RCD circuits, and 7 ms for the external garage RCD unit. There are various other columns like 'Loop Impedance', 'CPC-CPC ohms', 'Ph-Ph ohms', 'R1+R2 or R2 ohms'; they mean nothing to me but please let me know if they could help the diagnosis.

--
Terry, West Sussex, UK

Pondering this over a coffee shortly after hitting Send, I realised that I was wrong to imply the devices on this circuit were insignificant. I left all the devices in place when I applied the leakage. Amongst other things, I have an ancient large DC power supply in my shed/workshop (30A), permanently connected to provide automatic garden lighting at dusk. I'm wondering if perhaps some sort of inductive effect might be responsible? Could the sudden removal of power from that and other lower-rated transformers have had the effect observed? If so, my starting choice was poor, and I'll try another circuit. Or maybe disconnect the two plugs from the garage RCD unit.

--
Terry, West Sussex, UK