Setting an adjustable rcd?

[Knobhead]

Who specified this unit? They would be the first to ask.

This has some interesting reading http://www.switchrite.co.za/data/merlin_gerin_din_circuit_breaker_application_guide.pdf it also gives Merlin Gerin’s help line.

 

[Richard Burns]

Cheers Richard, yes that is the exact same control panel.

Downstream RCD is a different make to the Merin above and is not time delayed.

So to sum up its a case of testing the downstream RCD, finding what its tripping time is and adjusting the vigi accordingly.

Wozz

From Spartykus post I would like to say that the arrangement I think you have is:
Supply.....Your TDRCD......non time delayed RCD......Equipment.
I.e. the time delay is upfront and closest to the supply.

You cannot just measure the trip time as conditions could be different under a fault and change the trip time. You have a different make downstream so coordination is more difficult since they will not be designed to the same characteristics. You need to know the tripping characteristics of the down stream device and your RCD and work out the value of delay that will ensure discrimination.
GN3 recommends that the trip time of an RCD does not exceed 300ms if it is not time delayed, however the RCDs you are using may have different characteristics.
For instance, I do not know the model of RCD you have but this is something similar (may be the same) that specifies the trip times for the RCD

As you can see the maximum trip times are coordinated for each setting (and are considerably less than 300ms when not time delayed).
You will need to find similar information for both your RCD and the down stream one and if you have a maximum tripping time downstream of 200ms then your RCD could be 300ms and so on.
Do some research, get on google, find the information for your devices, apply them to your situation and you are then sorted.