mcb tripping with no load

irish bloke

Hi,

As heading says, it appears I have a mcb tripping with no load.
Moved into the house a few weeks ago and no issues with this particular circuit except for tonight.

There are 3 circuits for sockets all protected by b20 Hager circuit breakers. There is also a 63a rccb protecting the sockets.

Rccb and the other 2 socket circuits are all fine.
Circuit in question in the kitchen and 1 socket upstairs.
Plugged everything out of the circuits and the breaker is still tripping.
I'm thinking the mcb is faulty, but is there another possible fault?
Will prob swap one of the other mcb to that circuit tomorrow to test.

Suggestions welcomeðŸ˜

Randyleprechaun

A fault in the cabling of that circuit is most likely.

Insulation resistance test will give the answers

brightspark

Is it possible you have put up shelves/pictures etc since moving in.

You might have put a screw/nail into a cable?

irish bloke

Thanks for the replies.

I'm guessing if the live or neutral were shorted to ground the rccb would trip, which it hasnt.


As its a single pole mcb, if the live was open circuit (i.e. screw through it etc.) then nothing would happen as no current could flow through the circuit.

Am I right in saying then that the only way it could be tripping is if the live is touching the neutral (assuming no load is on the circuit and the mcb is not faulty)

EHP

irish bloke wrote:

I'm guessing if the live or neutral were shorted to ground the rccb would trip, which it hasnt.

Don't assume the RCD is working. Many out there that don't work. It could be a faulty MCB but you would have to complete an insulation resistance test to make sure the cable is OK.

Just as a note any work completed on a consumer unit in a domestic house is restricted works and should only be completed by a REC.

2011

An MCB (assuming it is not faulty) will trip on an over current condition. So excessive current in the phase (live) conductor. This is most likely due to a short between phase & earth or phase and neutral.

Ladybird book version:
An RCD (assuming it is not faulty) will trip due to a difference in the magnitude of current in the phase than the neutral in a given circuit. In a healthy circuit these would be equal. This imbalance is caused by some / all of the current returning to earth instead of the neutral. So a neutral to earth fault.

irish bloke

OK, got sorted.

Swapped the 20A mcb this morning with another 20A socket mcb and the problem followed the circuit - therefore mcb OK.

When I switched back on the breakers this morning the wife was in the kitchen and said she heard a bang from a certain socket outlet.

Disconnected the neutral from this socket with the intention of seperating the cores to see would the mcb reset and as soon as I pulled the connected cores out of the socket, the rccb tripped - neutral wires still connected together at this stage. Reset rccb and mcb and all good.

Put a new 2 gang socket at that outlet and all OK - never come across a faulty socket before, but there's a first time for everything I suppose.

Forgot to say I tested the rccb last night too and it tripped as expected. Going to replace this in the coming days though as a precaution.

Thanks for all the helpðŸ‘

Risteard81

Your haphazard diagnosis of this problem would suggest to me that you are not competent to be doing this work. Note also that without being a Registered Electrical Contractor it is unlawful for you to replace components in the Distribution Board (with a potential prison sentence). It will also render your insurance cover invalid.

EHP

irish bloke wrote:

Forgot to say I tested the rccb last night too and it tripped as expected. Going to replace this in the coming days though as a precaution.

How did you test the RCD just by pressing the test button? What about the other 6 tests needed. A new RCD might not be the safest option as again without testing you can't be sure it's functioning correctly new ones do fail tests also. Just wondering how much you value your own life and that of your families because in a worst case scenario that's what your playing with rather than paying a REC to complete the work.

DublinDilbert

irish bloke wrote: »

OK, got sorted.

Swapped the 20A mcb this morning with another 20A socket mcb and the problem followed the circuit - therefore mcb OK.

When I switched back on the breakers this morning the wife was in the kitchen and said she heard a bang from a certain socket outlet.

Disconnected the neutral from this socket with the intention of seperating the cores to see would the mcb reset and as soon as I pulled the connected cores out of the socket, the rccb tripped - neutral wires still connected together at this stage. Reset rccb and mcb and all good.

Put a new 2 gang socket at that outlet and all OK - never come across a faulty socket before, but there's a first time for everything I suppose.

Forgot to say I tested the rccb last night too and it tripped as expected. Going to replace this in the coming days though as a precaution.

Thanks for all the helpðŸ‘

You were pulling out the neutral connections from this socket with the power turned on?

Sorry how was the socket faulty? Sockets do go faulty, but have never seen one tripping an MCB.

mark085

Could be short circuit live to neutral
Do a continuity test

irish bloke

Folks,

Really surprised and annoyed by the condecending posts following my post stating the issue was corrected, particularly by Risteard81 and EHP .

Just for the record I am more then competent and qualified to work on electrical circuits.
I have certification to work on industrual electrical systems up to 1000VAC - this was awarded from LIT in 2007 and was the same written and practical exam as the final level 6 exam given to qualified electricans.. On top of that i have a level 9 masters complete in industrial automation and control.

I am fully aware of the regulations around working on domestic circuits, and while I believe its overkill and a way for sparks to frighten the bejeasus out of everyone, none the less it's the reg and probably a good thing

I asked the question last night for reassurance of where I was going and to be honest would have got there anyway.

The issue happened last night and i had a multimeter handy, if I thought I needed a mergger down the line, I would have got one in work.

In sumnary, im just really annoyed by a couple of keyboard warriors wrongly assuming someone has no idea about what they are doing and feeling it necessary to come on here and let it be known.

I am not a domestic electrician, therefore have no need to become registered, but am fully competent where required.

I hope to god the next person coming on here looking for help doesn't get the same imperious response

2011

@ Irish bloke:
Good to hear that you got the issue sorted. Like you I am qualified and capable of doing domestic electrical work but legally am not permitted to do it (as I am not a REC).

As this is the internet and posters could be advising someone of very limited experience I think it is prudent to state that there are dangers associated with working with mains voltage and the legalities surrounding this. However this can be done without laboring the point in a friendly and civil manner that is appropriate for a DIY forum.

Anyway on that note I think this thread has run its course.