M C B Settings

[AndyD]

'In' is the current rating of the MCB which in your case is 400A I assume.
'Io' is the course setting for the 'long time' protection threshold
'Ir' is the fine setting for the long time protecton.

You work out you overload protection using In x Io x Ir.

Isd is the threshold of the short time pickup. Some breakers you can adjust the time delay on the Isd point (0-0.5 secs max usually) but I don't see any adjustment on yours. .

Also some breakers have adjustment on the Ii threshold which is the point of Instantaneous short circuit protection, again yours doesn't appear to have this.

[mikilianis]

Thanks AndyD
Could it be that they are useing the incorrect breaker for the application,The breaker is supplying a Heat pump with two compressors eight fans and two pumps all the sums are correct, cable size, installation method, the breaker is correctly rated for the equipment what concerns me is that it is tripping open sometimes as low as 70 Amps not all the time though sometimes days in between having to be reset, the compressors start up with a delayed sequence so both dont start up at the same time the fans are also supplied via an invertor wich ramps them up so minimal inrush ?