Short circuit tripping RCD

logonuser1

Active Member
Your fault is on one of the following circuits
Sockets in Kitchen, Dining Room, Hallway, upstairs Landing and front bedroom.

you state that the mcb only protects those circuits , unplug everything from one room at a time and see if mcb trips , start in dining room .
 

logonuser1

Active Member
you will need to run a extension from your dining room to kitchen to power your fridge once you are sure the dining room is not the cause .
 
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Dancook

Distinguished Member
Your fault is on one of the following circuits
Sockets in Kitchen, Dining Room, Hallway, upstairs Landing and front bedroom.

you state that the mcb only protects those circuits , unplug everything from one room at a time and see if mcb trips , start in dining room .

I'm running an extension from the lounge to the fridge/freezer/hob - the lounge is on a different RCD.

There is currently nothing plugged into the sockets in any room on MCB circuit which trips, the last thing to be taken off was the dishwasher which I unplugged from the wall and then 10 minutes later it still tripped with a bang. (I realised some things i thought were hardwired just had a easy access switch that cuts off the socket behind the devices)

The last time it tripped was when i spoke to the electrician at 9:30am

I was told to set all the other MCB in the off position, and keep on the one that tripped and the RCD. it has not tripped since - Louise tells me she heard a bang when i was outside, but it didn't trip so I don't know if it was the board or not.

I think the plan after that is to add in the other MCB's one at a time to see if they are actually the cause.

### UPDATE ###

It just tripped like this, nothing plugged in anywhere on the circuit, so time to disconnect and tape up wires on underfloor heating now

although i had a look and i bottled it :D so many wires - i'll let the electrician know.

123499164_10164701810770227_6550491238383894356_n.jpg
 
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noiseboy72

Distinguished Member
MCBs have 2 tripping modes.
Over current - usually around 2x the rated current and the trip will fire in a few minutes.

Short Circuit: Instantaneous trip, normally at around 5-10x trip rating, depending upon the trip type.

If your MCB is tripping, it's either faulty or you have a serious fault somewhere and something is drawing far too much current. What value is the trip? It's a ring main I would imagine it's 32A. This means currents of 60A could be flowing around your system somewhere... I think it more likely that the MCB is faulty, but it needs a current clamp on the circuit, possibly with a recording function to see what the circuit is doing.
 

ufo550

Well-known Member
Not very impressed with your electrician, what test has he/she carried out on your fixed wiring & rcd?

Whilst unplugging appliances or isolating them might establish the fault(s), but once that’s proved inconclusive, a more systematic approach is required. A back to basic testing should be started.

You might have an insulation fault, your RCD might be faulty, there might be too much cumulative earth leakage for your RCD. You might have a fault on the other circuits (supplied by the other RCD), causing the this RCD to trip. You‘ll be very lucky to locate this particular fault, without systematic approach.

Appliances etc, must be isolated with both live & neutral conductors, just turning off the mcb will not suffice.

I would suggest, that now your mcb has been operated several times, by this fault, it’s probably not functional and should be replaced.

If your electrician is not at their best, fault finding, you need to find one that is. It might take some time (fault finding).
 
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Dancook

Distinguished Member
Not very impressed with your electrician, what test has he/she carried out on your fixed wiring & rcd?

The electrician hasn't charged me any money for his help so far. He popped over after a job after I called him on Monday, to test sockets and tape up some outside light wires and check a few things, he's since kept in contact to help try and narrow down the issue.

Whilst unplugging appliances or isolating them might establish the fault(s), but once that’s proved inconclusive, a more systematic approach is required. A back to basic testing should be started.

You might have an insulation fault, your RCD might be faulty, there might be too much cumulative earth leakage for your RCD. You might have a fault on the other circuits (supplied by the other RCD), causing the this RCD to trip. You‘ll be very lucky to locate this particular fault, without systematic approach.

Today he had me disable the other circuits (except for the one that typically trips) on the RCD, it still tripped. It took from 9:30am until early afternoon to find this out though.

Appliances etc, must be isolated with both live & neutral conductors, just turning off the mcb will not suffice.

I would suggest, that now your mcb has been operated several times, by this fault, it’s probably not functional and should be replaced.

If your electrician is not at their best, fault finding, you need to find one that is. It might take some time.

I should probably give him a paid chance to come over and spend time on it?
 
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ufo550

Well-known Member
Yep I think you should pay for him to come and test. If the RCD reinstates as soon as it’s been tripped, with appliances totally disconnected, could point to a faulty appliance.

However it could be a neutral - earth fault on the fixed wiring, that only trips the RCD, once an appliance draws a load on that circuit. Or it could be a cable has been pinched somewhere, where mechanical movement provides the fault. It could be many things, typically a simple fault, but sometimes hide to find. Keeping a diary of incidents, as he’s suggested might help, as does the mcb tripping circui, might be something to start point. But I would start at the beginning, testing wise.
 

Dancook

Distinguished Member
Yep I think you should pay for him to come and test. If the RCD reinstates as soon as it’s been tripped, with appliances totally disconnected, could point to a faulty appliance.

Trips if appliances are totally disconnected, but could be a faulty appliance?

I mean but there is one(two) appliance that i can't disconnect myself and it's the two underfloor heating thermostats which have been off for years.

However it could be a neutral - earth fault on the fixed wiring, that only trips the RCD, once an appliance draws a load on that circuit.

From what I understand electrician didn't think it was an earth fault due to loud bang, which he says is a short circuit.
 

Dancook

Distinguished Member
An earth fault can cause a dead short; it could be the appliances you can’t access. Ive missed the bit, why you can’t isololate them and the uf.

I took a look behind one of the isolation switchs for the underfloor heating, and there were about 7 wires, 3 earths, 2 neutrals, 2 live i think - I just wasn't sure confident with what to do to remove the themostats out of the equation.
 

Dancook

Distinguished Member
They don’t have something like this FCU?

yes that's what i keep calling the isolation switch obviously wrong :D but yes two of those

electrician has messaged to say it's the next step to disconnect UFH, but he'll call me in morning.
 

Dancook

Distinguished Member
Switching them off, should isolate the ufh. Unless it’s been connected by someone not knowing what they are doing.

Hope your electrician locates your fault.

Yes they've been switched off, and there's no power to the thermostat - but they don't have "double pole isolators" or something?

Will see what he says tomorrow, cheers
 

Dancook

Distinguished Member
I'll have a go at disconnecting the UFH/thermostat and taping up the wires..

Here are the shots of the fuse spurs

Do I just tape up all wire ends individually, except for Socket B where I tape the E1a+E1b together, L1a+L1b together and N1a+N1b together?

123540678_10164706517655227_3523331526876210266_n.jpg
123729761_10164706517740227_2628544116554060178_n.jpg
123775323_10164706517880227_818017790020071972_n.jpg
 

logonuser1

Active Member
why dont you just remove the fuse from the fused spur before you try disconnecting the N and E and then monitor the behaviour of the mcb marked downstairs ring that keeps tripping........i would try this first.
 

Dancook

Distinguished Member
why dont you just remove the fuse from the fused spur before you try disconnecting the N and E and then monitor the behaviour of the mcb marked downstairs ring that keeps tripping........i would try this first.

i asked the electrician if i could just remove the fuse to test, he told me it won't be a reliable test because it doesn't have double pole isolators or something.

but i will try removing the fuse as i haven't got wago connectors to go ahead with disconnecting it anyway
 
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Dancook

Distinguished Member
Don't tape anything up. Use push connectors like Wago's. It's easier and safer.

i don't have anything like that so i'll have to buy some, i guess i might then also need blanking wall covers/plates for the extra room to hide them away.
 

stevelup

Distinguished Member
Hang on a minute... MCB -and- RCD are tripping. This can only be a problem with the live side of things. A N/E fault cannot possibly trip the MCB.

So single pole isolators / removing fuses is a totally reliable means of isolating this issue.

I suspect you have a hidden junction box somewhere you don't know about that is full of water.

This really is a job for a professional.
 

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