Tripping out electrics!

Have a Crabtree consumer unit - MCB on one side covers lights, oven and smoke detector and never had a problem with this. On the other side is an RCCD master with three mini RCD's as goes:

1) electric sockets throughout the house except kitchen 2) electric sockets in kitchen and combi boiler 3) cooker hood fan.

We've been in this house for almost 1 year and in that time 2) has tripped several times between May and December 2009 all by itself and not associated with any specific device being turned on/off - but has not happened since 17th December 2009. Today though it was the master trip which governs all three of these which tripped. So it's impossible for me to isolate the fault to one circuit as they were all off.

Any ideas what could've done this?

Reply to
b17
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I think you need to check you are using the right words to describe the right things.

It is highly unlikey that an (singular) Minature Circuit Breaker (MCB) is going to cover lights, oven and smoke detector. I expect you have a main switch followed by three MCBs for lights, oven and smoke detector.

After that there is an Residual Current Device (RCD), bit like the main switch but with "test" button, followed by MCBs for the two sets of sockets and the cooker hood. Do the individual devices covering the two sets of sockets and cooker hood also have "test" buttons?

Reply to
Dave Liquorice

Apologies - you are correct. I meant to say MCB's.

No there is only one test button and it's on the master RCD paddle.

Reply to
Bear

It sounds rather like you have a classic "split load" consumer unit[1], with MCBs[2] protecting each circuit, and a single RCD[3] protecting the circuits most at risk of giving serious shocks.

Your trip of the single MCB would seem to be a simple case of either overload (too many appliances drawing too much current) or possibly an inrush current problem - one device in particular taking lots of current on startup and pushing the MCB "over the edge". What appliances have you got in your kitchen sharing this MCB?

The current problem sounds like a nuisance trip problem. See the wiki article for more details on finding this [4[.

[1]
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?title=MCB[3]
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?title=RCD#Nuisance_trips
Reply to
John Rumm

Thanks for the wiki links - been through them before when trying to sort trip problems last year. Yes indeed it is a split load consumer unit - can I clarify - by MCB are you referring to the master circuit breaker which covers the three smaller circuit breakers which are residual current ones? When the master switch was thrown, I was out of the house but the only things which would've been on are combi boiler, fridge and freezer. Nothing else was timed to switch on and it was daylight so the 500watt floodlight outside wouldn't have activated.

Reply to
Bear

It would be helpful if you would indicate the current rating of the MCBs for each of the circuits you described and the rating of the RCD (thats the one with the "test" button controlling the three MCBs and the trip current will be probably 30mA or 100mA)

Reply to
cynic

I think we may still be talking at crossed purposes here...

If you have the traditional split load arrangement you would have a master switch at one end of the CU, followed by some MCBs, followed by a RCD, followed by some more MCBs. At no point would there be a "master MCB"

RCDs should be easy to spot - they will have a test button. It may look like the square bit on the front of this (or something similar):

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usually be somewhere in the middle of the CU. The other wide device would be the main incomer switch.

The switch may look like:

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may have no marking except perhaps on and off, or it could include the max current (typically 100A) as in the picture.

The RCD will be marked with both a maximum current rating (probably 63 or 80A), and a trip current rating of probably 0.03A (30mA).

Ordinary MCBs will be marked with a letter and a nominal current, typically B6, B16, B20, or B32 (possibly C6 etc)

The other possible option is a RCBO - this is a combined MCB and RCD. Sometimes these are two units wide - or other times they are just taller (but the extra height is hidden in the CU so not apparent from the outside). If you have one of these it will have markings as per a MCB and a RCD, plus it will have a test button.

If the thing that tripped was the RCD (i.e. the thing that switches several circuits, but is not the main switch), the the likely culprit could be the combi. The combination of water and electricity in the same box being a common formula for RCD trips.

Reply to
John Rumm

cheers for the reply - to save more confusion and trying to explain elements which I don't fully understand I've uploaded a photo here:

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Reply to
Bear

The red master switch allows you to isolate everything at once, it will never cut out by itself.

The four MCBs at the left side will each only cut out when the total load on its circuit exceeds the rating (40A on the cooker, 6A each on the lighting and smoke alarm circuits) although they won't simply trip at e.g, 41A and 7A.

The RCCB in the centre controls the three MCBs to the right, it will cut out when there is any slight imbalance between Live and Netutral on those circuits, this is generally referred to as earth leakage.

The three MCBs to the right are the same as the other four, for their respective 32A rings, and the 20A (presumed) radial for the cooker extractor hood, they will each only cut out on overload, but if there is earth leakage on any one of them* the RCCB will cut out.

*the RCCB will also cut out if the total earth leakage on all the three right hand MCBs exceeds the limit.

So ... which MCB and/or RCB was cutting out when you had the original problem?

Reply to
Andy Burns

Red main switch, I assume this turns everything off Then you have 4 MCB's (as they have written on them!) for the cooker, two for lights and then smoke detectors. You then have an "RCCB" or otherwise known as an RCD. connected to this, you have three MCB's that protect the following circuits - 2 for sockets (one for the Kitchen sockets and one for everywhere else), and one for the extractor fan, the job of the RCCB is to protect the circuits to its right from earth leakage, so if you touched the live wire from one of your sockets, then this would trip, and you would have a better chance of surviving, but don't test this theory on purpose please!

You say that the Kitchen sockets MCB has tripped off for no apparent reason, this will trip for two reasons - if the total load that is passing through it is higher than 32A, or if it is faulty, and it is tripping at too lower current.

When it tripped, were you using a lot of electricity in the kitchen (Things that heat, like the dishwasher, washing machine, tumble dryer, kettle, toaster, Microwave, all use the most power - if you suddenly decided to turn everything on at the same time, it would probably trip.

Kettle - 3000w (13A) Washing machine - 2500w (11A) (during heating part of wash) Dishwasher - 2500W (11A) (during heating part of wash)

All that is already 35A, which probably won't make it trip, but put the microwave on too, and it is likely to.

Do you have any table lamps, or kitchen under cupboard lights that are on this same circuit - if the circuit was already heavily loaded, and you turned on a light that then popped the bulb, that could easily take it out.

Now the "new" problem of the "RCCB" tripping off could be down to a genuine problem somewhere, or maybe a spike in the mains. If it has just happened the once, then I wouldn't worry - if it keeps happening, then you need to look into it.

Toby...

Reply to
Toby

cheers guys - the original problem would throw the 2nd MCB from the right which controls the combi boiler and associated electrical sockets in the kitchen. This has happened 7 times since last May - no pattern to time - sometimes 4am - sometimes 4pm. It never tripped when something was switched on and we have run the gas hob, microwave, oven, dishwasher, washing machine, fridge & freezer, kettle and my wife has been taking a shower and it's never tripped with all that load. On Sunday the RCCB tripped (first time ever). Only the fridge, freezer, combi boiler could have been running - nothing else - we were out. Nothing on timer either. Mostly when the 2nd MCB has tripped we've been out - so guessing it has to be something on timer or with a thermostat (fridge, freezer or combi).

Reply to
Bear

Can you rule out the boiler - has it ever tripped when you know this was not actually running?

If so, then I expect it may be the fridge or freezer - is it practical to power one of these via and extension lead from a socket in the main house, to see if the problem moves to a different MCB?

You say a shower - as you don't have an MCB for an electric shower, I assume this is directly from the plumbing (not electric at all)?

You don't have one of these in the shower do you?

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Reply to
Toby

No - shower is run directly from the combi boiler. As for ruling any of them out, the combi, fridge and freezer are permanently on (ie. will switch in/out on thermostat) so without measuring temperatures impossible to say which device is tripping. Ultimately I will replace fridge/freezer in time when they fail and probably narrow it to a fault in the combi somewhere. But i've no way of removing them from the loop without losing the ability to freeze/cool food at present.

Reply to
Bear

Did think of that - but generally this happens every two or three months! So will have to put up with tripping over it for that length of time. Still if it solves the problem....

Reply to
Bear

I am not suggesting you turn them off, just run an extension lead from another socket in the house to one of these appliances, and then see if the tripping MCB changes to the main house MCB.

Toby...

Reply to
Toby

It's really the only way you can isolate the problem - I assume you haven't had any of the appliances blowing fuses?

It is good to check the fuses are correctly rated too, especially in the boiler - I expect that should have a 3A fuse, but may have been fitted with a 13A fuse. - Check the manual to see what it should have (or post the make and model here, if you don't have the manual!)

As I said before - is there any time you can say the boiler was not running, and it tripped, if so, that will rule that out.

The only other thing you can do, is get the MCB changed or swapped over, to see if the fault moves - I wouldn't recommend you open the consumer unit yourself, unless you really do know what you are doing though (no offence, but from your confusion with MCB's and RCD's I would suggest you get someone in to do it, if you want to try that!)

Toby...

Reply to
Toby

Just had another thought, if you have a dial on the fridge and freezer that makes a small click when you turn it up/down, then next time it trips, you can turn the temperature on each of them UP and see if it clicks - if it does, then it is likely that appliance was running when it tripped (assuming you test it when it trips out, not hours later!)

You may see a pattern to it given enough time.

Toby...

Reply to
Toby

Cheers Toby - I can guarantee I won't be playing with the consumer unit. Although I will check the appliances have the correct fuses - good idea. I don't fully understand the idea behind changing the fridge temperature until it clicks though?

Reply to
b17

Good good, better safe then dead if you don't know what you are dealing with!

The idea with the fridge is, when the fridge is cooling, the thermostat will have clicked on, therefore if the power trips off, this will test if the fridge was running just prior to it tripping.

If the thermostat clicks when you turn the temperature up (so the way you turn it to make the fridge warmer) then the fridge was probably cooling when it tripped, if it does not click, then the fridge probably wasn't cooling, so you can try something else.

If you have a fridge and freezer with an electronic display, then you cant really test this easily, only if it has a manual dial that you can hear click when it is demanding cooling.

Hope that helps!

Toby...

Reply to
Toby

Even that is not definitive - much depends on the load on the alternate circuit.

Reply to
John Rumm

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