Another RCD Tripping problem

[eskimo39]

Hi guys, last week my neighbour asked me to look at their consumer unit as it had tripped 4 times in one day.
The side that tripped had on it:

• Kitchen Sockets (1xMicrowave, 1xFridge, 1xFreezer, 1xKettle & 1xWashing Machine)
• Hob
• Upstairs Lighting

I tested the RCD and it tripped in 26ms and a ramp test showed 29mA so it looked like it was o.k.

I thought the fault would most probably lie with one of the appliances and with the washing machine having a heating element in it, assumed this the most likley. I explained if it tripped again they should plug the washer into an extention lead and power it via the living room sockets from the other RCD. If this didn't work, I planned on trying the other appliances.

However the RCD tripped so they unplugged the washer and powered it from the living room sockets as discussed. After a while this tripped the other RCD so I thought that had solved the problem and it was the washing machine. However 5 minutes after, with the washer still on the living room RCD the original RCD also tripped??????

Does anyone know what could be causing this? I thought when the other RCD tripped via the extension lead that would have meant the washer was at fault. 5 minutes later the original RCD tripping has put doubts on this.

Does anyone have any other ways to test???

Cheers

 

[UNG]

Fridges and freezers can cause problems with the auto defrost function as the heating element is only operated intermittantly on a timer

This is one of my first checks if an RCD trips intermittantly problem is a PAT test does not normally find the problem as the auto defrost resets and it can be hours before it happens again

 

[jmtisme]

Once had a problem with a faulty extension tripping RCD only happenned when a half decent load was pulled through it

 

[unemployed]

Cheers Guys,

I am 99% certain the fault is an appliance, the only puzzle is why when the washing machine was put on a socket powered by the other side of the board, it tripped as expected but then the original side tripped as well???

RCD's tripping cause is ground fault.
Maybe you are right, one of appliance is faulty.
For example washer is faulty, did you check washer's earthing?
or you can check that living room extension's RCD rating, I thought the main reason cause the original RCD's tripping is RCD's lack of disciminative, that means it is too sensetive, it's rating too small,cannot dicriminate the fault current caused by faulty appliance.
Sensitivity

RCD sensitivity is expressed as the rated residual operating current, noted IΔn. Preferred values have been defined by the IEC, thus making it possible to divide RCDs into three groups according to their IΔn value.

• High sensitivity (HS): 6 – 10 – 30 mA (for direct-contact / life injury protection)
• Medium sensitivity (MS): 100 – 300 – 500 – 1000 mA (for fire protection)
• Low sensitivity (LS): 3 – 10 – 30 A (typically for protection of machines)

so, you should choose bigger rating RCD replace consumer unit's RCD.
the ultimate solution is check the faulty out the circuit, than check circuit groud is propally connected, just in case.
good luck!

 

[Sintra]

You can't replace with a higher rated RCD it has to be 30mA to comply wiyh the regs.

 

[Deleted member 9648]

RCD's tripping cause is ground fault.
Maybe you are right, one of appliance is faulty.
For example washer is faulty, did you check washer's earthing?
or you can check that living room extension's RCD rating, I thought the main reason cause the original RCD's tripping is RCD's lack of disciminative, that means it is too sensetive, it's rating too small,cannot dicriminate the fault current caused by faulty appliance.
Sensitivity

RCD sensitivity is expressed as the rated residual operating current, noted IΔn. Preferred values have been defined by the IEC, thus making it possible to divide RCDs into three groups according to their IΔn value.

• High sensitivity (HS): 6 – 10 – 30 mA (for direct-contact / life injury protection)
• Medium sensitivity (MS): 100 – 300 – 500 – 1000 mA (for fire protection)
• Low sensitivity (LS): 3 – 10 – 30 A (typically for protection of machines)

so, you should choose bigger rating RCD replace consumer unit's RCD.
the ultimate solution is check the faulty out the circuit, than check circuit groud is propally connected, just in case.
good luck!

What a load of tosh......The first and essential step in tracing RCD tripping is careful and systematic insulation resistance testing.

 

[WayneL]

Hi guys, thanks for all the responses. IR testing on all circuits came up fine. Also once we changed the washing machine to a socket powered by the other side of the board via the extension lead, that side tripped first so the chance of lighting being at fault on the other side would be limited I'd have thought.

Hi Eskimo,

How did you perform the IR tests?

What is the earthing system?