RCBO

[Albert]

Hi,
RCBO trips but not in the required time, is there any fault on the circuit that could cause this or the RCBO is faulty?

 

[Taylortwocities]

RCBOs and RCDs must be tested with their circuit disconnected. Otherwise leakage on the circuit can affect the test results.

If it still tests outside the spec then it needs replacement.

Tell us what results you get when you test it again.

 

[SgtTrojan]

Either:
a) Faulty RCBO
b) A very high resistance (that would fail Zs verification for sure)

A colleague suggested "ramp testing". The increase in test current should indicate the point at with the device disconnects. Allegedly an RCD or RCBO will disconnect around the 18mA mark but I have never carried out such testing to confirm.

 

[1john]

Test the RCBO in isolation, you arn't testing the circuit with an RCD tripping test, you are testing the correct operation of the RCD and that it meets the required disconnection times.

 

[SgtTrojan]

Yes, so if testing on the load side terminals of the RCBO ignore b) above.

 

[sparkiemike]

If there is any capacitance on the circuit (e.g. from equipment that is still connected or a very long circuit) then the capacitance could keep voltage on the circuit long enough to give you a duff reading - think about it - the tester is waiting to see the voltage fall to zero (contacts open) to determine disconnection time.

Also GN3 advises that all loads are removed for the RCD test!