One socket trips mcb

[Paul W]

Hello,

New to this forum. I hope someone can shed some light on this problem.

There is an odd wiring arrangement in the house where one ring has a mixture of upstairs and downstairs sockets, another ring has the remaining downstairs sockets and there is one radial circuit to one upstairs socket. It is this radial socket which is causing the problem.

Very intermittent fault, probably happens about 2 or 3 times a week, when something is plugged into the socket the mcb trips. This will happen for anything that is plugged in, so it is not the fault of the appliance. The socket has been changed and the cable where it enters the box and at the other end where it enters the fuse box has been checked for damage. A socket tester has been plugged in and shows no earth, neutral or live faults.

Any ideas most appreciated.

 

[leekemp85]

A socket checker will not tell you if there is a fault, you need to do more tests insulation and zs

 

[zupos40]

Hello,

New to this forum. I hope someone can shed some light on this problem.

There is an odd wiring arrangement in the house where one ring has a mixture of upstairs and downstairs sockets, another ring has the remaining downstairs sockets and there is one radial circuit to one upstairs socket. It is this radial socket which is causing the problem.

Very intermittent fault, probably happens about 2 or 3 times a week, when something is plugged into the socket the mcb trips. This will happen for anything that is plugged in, so it is not the fault of the appliance. The socket has been changed and the cable where it enters the box and at the other end where it enters the fuse box has been checked for damage. A socket tester has been plugged in and shows no earth, neutral or live faults.

Any ideas most appreciated.

Have you preformed an insulation test on the cable, how old is the wiring, is there any dampness in the wall etc.

 

[Paul W]

Hello,

Thanks for the speedy replies.

Not sure of the age of the cable but is grey solid core. Where the cable runs damp should not be an issue.

Your replies lead to the cable itself (maybe damaged insulation hidden somewhere. I'll just replace the cable as the run isn't too bad.

Thanks for pointing me in the right direction.

Paul W

 

[zupos40]

Hello,

Thanks for the speedy replies.

Not sure of the age of the cable but is grey solid core. Where the cable runs damp should not be an issue.

Your replies lead to the cable itself (maybe damaged insulation hidden somewhere. I'll just replace the cable as the run isn't too bad.

Thanks for pointing me in the right direction.

Paul W

I would test the cable first, before replacing, if insulation resistance is satisfactory, then I would replace the breaker, I have known old mcb to trip because the thermal overload part is damaged.

Mcb and Cb have Two protective components thermal for overload and magnetic for fault protection, sometime if the the breakers old and has been tripping excessive, it can deteriorate and become faulty, I had found the cause can be caused by person switching back on without clearing the fault.

 

[Paul W]

Hi zupos40,

Sorry, just realised my typing error!! It's the RCD (63A, 30mA) that trips not the MCB. When the fault occurs the MCB stays switched on.

I do not have access to the test kit for checking the cable insualtion and so have to assume the cable is OK for now.

Paul

 

[ICE]

Megg it

 

[Paul W]

Hello ICE,

Last time I megged anything it was in the 80's (with an avometer I think it was called if I remember?). This is when I could rewire my house and it was all legal to do so. I'm not a practicing electrician and so do not have any of the kit required to test the cabling.

Thanks for all the replies. I'll change the RCD and MCB as they were cheapos 3 years ago and may need replacing (thanks zupos40 for the advice on that). If that doesn't work I'll get an approved electrician in to change the cable [ to keep it legal and all that ].

Paul W

 

[mrloy99]

Hi zupos40,

Sorry, just realised my typing error!! It's the RCD (63A, 30mA) that trips not the MCB. When the fault occurs the MCB stays switched on.

I do not have access to the test kit for checking the cable insualtion and so have to assume the cable is OK for now.

Paul

you could check that the neutral is connected to the correct "rcd dedicated" bus bar in the consumer unit and that all connections are tight.

 

[Paul W]

Hi mrloy99,

Good advice. Had a similar problem at my last house where the electrics stopped tripping once I moved a neutral to another bar in the consumer unit. In this case, the rcd would trip whenever I turned on the lights (all the mains and lighting circuits went through the one rcd). No idea why this would happen. Two neutral bars connected by a short length of cable and one RCD....

Thanks,

Paul W

 

[ICE]

You say you have no megg so if you have a LROM then you could open both ends of cable and see if you get a reading of any sort, you should get an open circuit, its just a pointer not a proper test...

 

[tigerpaul]

It needs to be IR tested.

Sounds like it could be an old cable, maybe it has been in contact with polystyrene thermal insulation over a long period, which has caused the cable insulation to break down due to chemical reaction??

Maybe the cable has been chewed by vermin?

 

[ian.settle1]

you could check that the neutral is connected to the correct "rcd dedicated" bus bar in the consumer unit and that all connections are tight.

Or it's not connected to a non RCD circuit.

 

[Paul W]

Hi,

Not sure how to add in quotes to answer the questions yet.................

The trouble is the problem is intermittent so the readings will show open circuit (ICE reply)

Mice is a possibility as we had to poison a few last year (sorry to all those animal lovers but two small children and mouse droppings don't mix)............(tigerpaul)

Not sure about this one. All sockets and circuits go through the RCD...............(ian.settle1)

Thanks for all the replies.

Maybe it would be easier to call out an electrician. There seems to be plenty around who have time to answer this forum question

Paul W

 

[Mac]

Could be a loose connection in a J/B under the floor