Basic query about tripping fuse box

[Dinklerdo78]

I was wondering if anyone could help me with a query. About a week ago I found upon waking up trying to use appliances downstairs in my house that none work. I went to the fuse box. Being a complete novice in this area I simply flicked up the one switch that was down (marked "RCCB") and hey presto everything worked again.

I was away from home from Friday until Monday evening. When I returned I found that the appliances downstairs (including the fridge/ freezer) were not working. I again returned to the fuse box. This time I paid more attention. The switches marked "ground floor sockets" and "RCCB" were both turned to off. Again I flicked the switches to on. Things worked for around 30 minutes and then the system tripped again. I then began to look into the issue online. I have tried the method of trying to identify a faulty plug or appliance by turning everything off and then putting on each plug one by one. I haven't been able to identify a faulty device/ plug using that method. I have now turned the fuse switches ("ground floor sockets" and "RCCB") back on multiple times. Each time the appliances will work for around 30 minutes before tripping again. When I woke up this morning I found the two mentioned fuse switches turned off. When I attempted to turn them back up I noticed some sparks/ flickers of light behind the fuses.

Am I looking at something other than a faulty plug or appliance here? Should I persevere with trying to identify the faulty plug/ socket/ device in question? Or is it time to call in a professional?

I've attached an image which shows the fuse box after I have switched everything back to "on".

Many thanks

[Someone-Else]

Just saying ................FYI

The thing marked as RCCB is better known as RCD (As if that explains everything )
The other "Fuses" are not fuses, they are MCB's (Explanation coming)

A Fuse is a piece of wire in a holder (of some description, there are lots) when something goes wrong (eg nail gets put through a cable) the amount of current that flows is so great that the fuse wire literally melts. (if it is contained, it would be normal for it to go bang as well) When the wire melts it breaks (funny that, since it has melted) as it has broken no more current can flow, so saving everything else. Once the fuse has blown the wire has to be replaced (That is it in principal)

An MCB is "a fuse with a switch" in that once it blows, instead of melting you can switch it back on again (There is a whole lot more to how it works, but as before that is it in principal)

An RCD is like neither a fuse or an MCB. It does a very different job.
When a fuse or MCB blows it did so because too much current flowed. An RCD doesn't care how much current is flowing* it IS interested in WHERE the current is flowing. If the current flows up one wire and back down the other, the RCD is happy. If current flows up one wire and not all of it comes down the other wire that is an imbalance and that upsets the RCD so it "blows" and in so doing it turn off the electricity.
The question now is where did that electricity go? It went to earth, that could happen if a socket was damp/wet or you touched it by accident. This is known as a Leak (Just like water does if a pipe gets a hole by a nail etc)
One difference being that in order for an MCB to trip (Blow) it may need several Amps flowing for a second or two before it trips, and RCD will trip in less 40 milliseconds (It takes you 100-150 milliseconds to blink) with only 30mA flowing (1,000 milliamps =1 Amp)

So now you should have a very basic understanding of a Fuse, and MCB and an RCD

So if an MCB and an RCD is tripping, you have something very unusual (That said it may just be a spike caused by what ever trips the MCB) Yes the easiest thing to do is unplug everything and put them back one at a time, the theory being as item x is plugged in and the MCB trips you have found the culprit, as nothing happens in your case I would suggest you do it again, but take longer between plugging stuff in, Also has ANYTHING been altered in the last couple of weeks? new carpet, new picture hung, new washing machine ANYTHING? Also before you plug something in look at its cable has it been damaged or gnawed? or is you tv / new fangled table light anything else sitting a puddle of water?

[Neelix]

Could be an accumulative issue of earth leakage across so many circuits.

This is why consumer units like this are a bad idea

[wine~o]

Given the 30 minute time delay after resetting my best guess would be the fridge freezer as the culprit. Does the cooker isolaton point have a combined socket ? If so is it possible to plug the fridge/freezer in there via a suitable extension lead ?

If yes do that and switch back on at the CU. If the rccd trips and the downstairs sockets don't then you know that the fridge freezer is the culprit.

[Dinklerdo78]

Thanks very much for this. As I say I really don't know anything about electrics. This gives me some useful background and suggestions as to how to remedy. I've not had any new work done. The only thing I can think is that water builds up periodically at the base of the fridge, underneath some trays. I don't know if there is a possibility that some of that water could have gone down the back of the fridge and caused issues. Is that a common occurrence? Thanks again for your help

[Dinklerdo78]

Thank you for all of your replies. I can't work out how to respond individually. Unfortunately, the cooker isolation point doesn't have a separate socket. Maybe the fridge is the culprit given the gathering water around the trays at the bottom of the fridge. Trying to sort this while doing the day job. Will look at resolving this again tonight. I may be back on the forum!

[Neelix]

If the MCB and the RCCB are tripping that points more at a short somewhere ..........

Unplug as much as you can and especially if anything is outside, or in a garage or shed.

[ericmark]

Forgetting the tripping RCD for a minute, for the MCB to trip one needs a good fault, nail in cable, rats chewed cable, and in the main a 13 amp fuse will rupture before a B32 MCB trips.

So although it could be an appliance, more likely a fault with fixed wiring, and if it is an appliance then likely one with a 13 amp fuse not a 3 or 5 amp, so that means unlikely caused by the freezer.

Likely triggered by movement, either a floor board being stepped on, or a central heating pipe expanding, if there was a fault to earth large enough to trip the MCB then you would never be able to reset the RCD, your not looking at water, to allow that much current to flow to trip a MCB would need a lot of current, not just some thing damp.

Given the 30 minutes delay, I would expect a central heating pipe has expanded and shorted some thing, one hopes not rodents, so one has to consider what work has been done over the summer, that's the first area to look in.

If the MCB was not tripping then I would be looking in a complete different area, you clearly need to unplug anything not in use, to eliminate them, maybe turn off central heating and see if still trips, I had one in daughters house, it was the screw holding the socket to the back box touching a wire where the installer had not been careful with their knife when stripping cable.

To find it I had to split the ring final into smaller and smaller sections, and use an insulation tester, set to 1000 volts to increase chance of arcing. With the fault I found in mind, removing each socket while dead one by one one may be lucky as see the fault, since happened so many times likely some signs of burning.

I have had a socket damaged due to water ingress, and warped the plastic, but only tripped RCD not the MCB so that seems unlikely.

[aeromech3]

When I attempted to turn them back up I noticed some sparks/ flickers of light behind the fuses.

The experts above me might zero in on this, in my experience it is not normal except when there is something adrift in the back of the CU such as a slow cooking mouse body!
(or in my other overseas experiences a gecko).

[OnlyMe]

One difference being that in order for an MCB to trip (Blow) it may need several Amps flowing for a second or two before it trips, and RCD will trip in less 40 milliseconds (It takes you 100-150 milliseconds to blink) with only 30mA flowing (1,000 milliamps =1 Amp)

To add to that and correct a few minor errors.

You slipped up on the RCD trip times for a 30mA RCD. It's 300ms maximum trip time at 30mA and 40ms maximum trip time at 150mA.

The few seconds for a MCB to trip you referred to is due to overload (ie the thermal trip of the MCB) and would typically occur on an overloaded circuit such as too many appliance plugged into a socket circuit. This will take at least 15 seconds to occur even on a very highly loaded circuit

However in a short circuit scenario (over current protection) the MCB relies on a magnetic trip and because the current will be many hundreds of amps it will trip in 20 milliseconds.

Now a LN short should not trip an RCD so the OP is looking at a LE fault as both MCB and RCD are tripping.

The reason both trip and not one before the other is due to the 20 milisecond time of a 50Hz AC cycle and it can take out one one each half cycle