Sockets tripping mcb not rcd.

[Newinthegame]

Hi there folks.
thought I had this one sorted but doesn't seem so. Called to domestic dual rcd db. Mcb tripping straight away on 'kitchen sockets' rcd does not trip! Ir test less than 1mohm. I thought I had it when I found a fault on one of the ring main legs. So with the customers consent downgraded breaker to 20 amp disconnected faulty leg and power now back on to sockets....but now as a radial. Called by customer to say sockets off again....rcd ok but mcb will not turn on.....'flash from breaker when you try to switch on'
Any ideas? Before I left radial IR readings all ok, appliances all plugged in, switched on and running fine.

 

[JUD]

Could be faulty appliance. Have they tried unplugging everything to see if it will stay on??

 

[telectrix]

it's obviously a short L-N or an overload. unplug everything. IR L-N. if OK, plug in appliances 1 at a time.

 

[Newinthegame]

To trip mcb and not rcd would mean overload or short circuit right? Will ask customer if any appliances were running at the time.

 

[sjm]

What they said!

 

[nickblake]

check for a trapped live in a socket they can pop up due to movement of the socket it could well be a broken wire thats shorting out , remove all the appliances and test the circuit , do a continuity test between L and E and L and N see if you get a reading , if not then as tel has said it could be an overload

 

[SirKit Breaker]

The RCD will only trip for earth leakage, it wont trip for Short Circuit or overload. I guess you are called "newinthegame" for a reason, so just in case i will explain, Short Circuit = fault between live conductors, Earth Fault = fault between Live conductor and Earth. I only point his out, not to undermine your knowledge, but it often gets forgotten, and some people don't know the difference anyway.

Cheers...........Howard

 

[Swicade]

Have you checked for any built in appliances that may be plugged (built in Dishwasher/fridge/etc) things often missed due to looking like normal kitchen cupboards. Could be a fan assisted oven plugged into the ringmain,hob ignitor (if gas hob).

Only afew suggestions but things easy missed.....9/10 it is an appliance issue especialy in a kitchen.

 

[craigj85]

sounds like a faulty toaster/microwave/fridge. for example when the toaster is being used it could be drawing a fault current which is tripping out the circuit. if the mcb is tripping with a bang then something is faulty. that is why it wouldnt show itself until the toaster is switched on or the fridge refridgerator kicks in or the washing machine is used etc. thats my theory anyway i would start by looking at that. i wouldnt think it was a live to earth or neutral to earth fault on the circuit as this would prob trip the rcd as well plus youve done an IR test so that rules that out.

 

[ExArmy]

go round and check everything on the ring yourself, don't take the customers word for anything!

 

[steveberry11]

You have down rated the circuit from32A to 20A have you taken a load reading.
The problem may be an overload.

 

[marcusone]

Faulty appliance is one option. It could also be a loose connection. Check mcb / socket terminals are tight. You say IR was ok but were earth loop readings unusually high for circuit length ? Could indicate a loose connection. Let us know the outcome.

Sent from my HTC One X using Tapatalk 2

 

[Grants]

I bet my back teeth its either the washing machine or the dishwasher.

 

[pjcomp]

Did you also check the basics with the customer - hung any good pictures lately? Drilled any holes lately?

PJ

 

[vernam616]

Call an electrician perhaps?