tripping main rcd

[galv]

Hi. moved into a new property recently and now the rcd keeps tripping.
On the circuit 3 mcbs.one is a shower, one a couple of upstairs sockets, and it seems on the third a built in electric cooker with seperate electric hob and three sockets (which must be tapped of at some point.)
The rcd won't stay up even after i turned the cooker switch off and unplugged everything from the sockets, only when i fully disconnected the circuit to the cooker did the rcd work and the power was restored to the other two circuits so i assumed this was the faulty circuit.
out of curiosity i reconnected the cooker circuit and everything functioned correctly the sockets worked and were checked with a socket tester, the cooker worked(forgot to mention the hob is fully disconnected due to fault) for about 2 hours then the same happened.
Could the rcd be faulty and any way of checking?
Any other way of finding this fault or is it a rewire of the circuit?.

 

[Big_Spark]

galv, it sounds like there is a fault in either the cooker or the hob,however it could be part of the bodged socket extension taken from it.

Sockets, with the exception of one built into the cooker control panel, should not be spured off a cooker circuit. It is potentially dangerous as the cable supplying the sockets is not rated at anything like the fuse for the cooker circuit. This is a potential fire hazard as it is possible to overload the cable very easily.

This could be why the RCD trips, but probably not.

I would urge that you call in an electrician to break the circuit apart and test every part of it for a fault, then also split the sockets from the cooker circuit to their own circuit.

When you call the electrician I would ask them if they are able to perform a PAT test on your cooker and hob to see if this has the fault on it.

 

[galv]

Thanks fwl. i have found that the fault is the 6mm cable between the last junction box to the spured socket {there were two junction boxes within 18" of each other feeding three sockets, now disconnected)and the junction box that then splits off with two 6mm cables to the oven on one side of the kitchen and the hob on the opposit side.
So i am going to run a new 6mm cable but can the cable be split this way to oven and hob?
Now the sockets,i need to use these so can i take them back to the cu with a single 2.5mm and wire them as a radial? as two of the sockets are surrounded by tiles so can't get another cable in too make a ring,if possible what fuse rating and type,a fridge freezer and microwave will use two of the sockets

 

[Big_Spark]

Galv, glad you found the problem without too much hassle.

Regards the radial circuit, 2.5mm2 will be sufficient but I would put no greater than a 16A MCB in the board, or alternatively, You could get away with a 20A 100mA rated RCBO as this would certainly protect the circuit and yet not suffer nuisance tripping that the fridge/freezer may cause (some do, some don't)

 

[galv]

thanks fwl. could you please also answer the other question, of the best way to connect a built in leccy oven on one side of the kitchen and 4 ring leecy hob on the opposite side? the way it was is single 6mm from cu split in a junction box in the kitchen