Mcb tripping...?

[biggal5]

Hi,
ive read a lot of posts on here regarding mcb tripping and still need advise please. I have a kitchen ring tripping the mcb. I realise that 9 out of 10 times its an overload problem however I've unplugged all appliances and the mcb doesn't even stay on. From the other posts it seems like another cause could be a L-N fault shorting it out. I've done an Ir and although not perfect results show >100Mohms. I've also removed all cover plates and tested each cable in turn and insulation test seems fine from each cable.

I've done a full set of tests on the circuit with continuity, insulation & Zs @ each socket and all test fine.?!

any advise you can provide will be very helpful and thanks in advance..

all seems fine for awhile and then mcb trips every 10 mins until it gets to the stage of not even staying on when everything is plugged out? To me it seems like an overload problem to start with and then turns into L-N fault but I very well could be wrong. Any help welcomed..

owners say say it happens randomly and not when a certain appliance is plugged in.?

ive ordered another mcb but is it likely to be that? Thanks

 

[Marvo]

Have you put a clamp meter on the circuit? Have you checked you haven't got the busbar outside or on the wrong side of the clamp so the termination is getting hot? If it's tripping and there's no load on the circuit replace it or try swapping it with another one of the same rating in the CU just to prove it's at fault.

 

[biggal5]

I've put a clamp meter on and it's ogetting 18.5amps or so... This is with radio, toaster, kettle, fridge, oven, w/m, dishwasher and microwave all on.. Customer says she never has all this going at once but I thought I'd do it just to test.. Also it's a it difficult to look under the busbar termination but very sure I got a good connection and didn't miss. Could it be that the washing machine & dishwasher are plugged into the same soviet via a short extension lead? Thanks for your reply.

 

[Darkwood]

You need to find out if the washing machine is hot water fed or a cold feed with the machine doing the heating, same with dishwasher if they have both options (not sure), when you test the load half these things won't be in their heating stage possible and you also mention oven... if this is over 2kw then it should be on it own circuit not plugged into the ring.

Take what the customer says with a pinch of salt here, you be surprised how much she's loading it up without thinking about what she has on it, its like when the women pops a few stone on and says shes eating less :wink5:

Just to rule out an unlikely cause swap the ring mcb over with another in the board to rule a faulty mcb out.

 

[biggal5]

Thanks for your reply.. My fault; there's a washing machine & tumble dryer on that one socket... Via extension lead.. Very helpful replies tho as I'll check these when I return. Just abit baffled as even when they are all plugged out the mcb doesn't stay on and switches off straight away.. Could this be if I wait a few minutes to let cables cool down before switching back on? Thanks again.

 

[PEG]

Hi dude,i have had an identical issue before,which i have described before...with two previous sparkies having jacked...

The circuit would trip the MCB,once every month,every hour,or prevent switching on till hours later.

All standards tests,showed no problems,and the customers' comment on increased tripping when weather was warm,lead me to start a physical examination,in the downstairs area,which got the warmest,which was the conservatory.

The third S/O face-plate,which i removed,had a fixing screw,with a knobbly,welded end....

It was bizarre that it had repeatedly gone from a short,sufficient to trip the 32A MCB,to a clear IR test...but it had.

My advice,would be,to listen to the customer...but ONLY to bear this in mind,and then to do your own CSI investigation,of a "hands-on" nature.

 

[plugsandsparks]

MCBs do fail and can fail to reset even with no outgoing cable. Do the checks on load as suggested but rule out nothing. I probably change one or two genuinely faulty MCBs a year so not common but do happen. Other causes have been cable damage fwiw

 

[Darkwood]

An overloaded mcb will trip with the thermal trigger, if reset quickly the thermal trip component is still hot and will trip quicker if the same load is introduced, the time current curve will become shorter if the mcb isn't allowed to cool.... its sound like overload by what you list and describe, she needs to stagger the loads in the short-term and I would suggest either adding a few radials for dryer and oven for a long term solution.

 

[Richard Burns]

Thinking on the thermal trip side, is the connection to the MCB OK, if there is a high resistance joint at the MCB the heat can cause it to trip.
You are certain it is an MCB and not an RCBO?

 

[markc123]

Reading through all this i agree with the above. Seems to me like its overload, and the increased overload over weeks, months, years ect.. has knackered the MCB to the point where it trips far quicker than it should.

You can normally get a feel for an MCB with the trip button, if it feels loose its nearly always k-nackered.

Examine the circuit, see what's being plugged in - tot up the wattage of whats being used, and go from there. May need a new circuit, or things splitting up ect...

 

[Octopus]

What make and type of MCB is it?

 

[biggal5]

Thanks all... I thought at one stage it was the connection from th mcb to the busbar not properly inserted as the cu is very high level and all boxed in... But I've made sure it's fine by proper checking all around it.! Double checking. The mcb does flick very easily, literally only have to lightly touch the switch and it goes, so from what you've said could be knackered mcb. Customer said all was fine until it tripped about a week ago... Then it tripped quite regularly.. No new appliances were bought or used on that circuit..!?
its a CPN MD132B B32amp.. Split RCD board..

thanks again all, very helpful.. Going back Thursday to investigate more..!

 

[Simonslimline]

Thanks all... I thought at one stage it was the connection from th mcb to the busbar not properly inserted as the cu is very high level and all boxed in... But I've made sure it's fine by proper checking all around it.! Double checking. The mcb does flick very easily, literally only have to lightly touch the switch and it goes, so from what you've said could be knackered mcb. Customer said all was fine until it tripped about a week ago... Then it tripped quite regularly.. No new appliances were bought or used on that circuit..!?
its a CPN MD132B B32amp.. Split RCD board..

thanks again all, very helpful.. Going back Thursday to investigate more..!

For the price of an MCB maybe worth replacing it seeing as it has been subject to excess current multiple times maybe?

 

[biggal5]

Got one ordered in... Prob knackered but gonna look foolish if it doesn't solve the problem... Already getting cursed down cos didn't resolve it on first visit.. Difficult customer Not gonna like it if new circuits gotta be put in...

 

[Simonslimline]

Got one ordered in... Prob knackered but gonna look foolish if it doesn't solve the problem... Already getting cursed down cos didn't resolve it on first visit.. Difficult customer Not gonna like it if new circuits gotta be put in...

All part of the job role mate.

 

[Farmelectrics]

interesting read let us no the outcome

 

[markc123]

If you only very lightly touch the MCB and it trips its a knackered MCB so you've done the correct thing ordering a new one.

This to me tells me that the MCB has been exposed to overload for quite some time. More investigation work is needed on the circuit. What size conductors are they, can you upgrade the MCB? Does anything need splitting?

I wouldn't just replace the MCB and hope for the best, might be okay for a year or so but long term you need to get to the root of the problem.

Mark.