Right guys here we go!
Assume that these devices you reffer to are Mccb type!
Ir = adjustable overload setting, this is adjustable from 1 breaker full rated current down to .75, eg, 100amp breaker would allow adjustment from 100 amps down to 75amps allowing you to match the breaker directly to the load. As pointed out by Ron these devises ar normally rear end and are only fitted to protect large chunks of an installation or perhaps a large piece of equipment that has its own individual overload and protective devices fitted in the panel. This is where the cascading comes in you need to look at all upstream devices to see at what point they operate then set up your device accordingly to allow them to operate without bringing out the main breaker. Best way to look at it is that the device in the egsample is a 75amp breaker allowing you to trim it up to a 100amps bit like your motor rated fuses.
(Im) Not so sure about we use different terminology (BSEN 60947-2) I think it might be reffering to Short time tripping setting current (isd) this adjusts the instantaneouse tripping threshold.
Hope I made sense guys, but I can't stress enough what Ron says though. Do involve the manufacturer they have run destructive tests on all of this gear and produced curves and data to assist with setting up of all of these devices. They are not much use if not set up correctly. Another thing to bear in mind don't use the curve from one manufacturer as a guide to other breakers there can be subtle differences.
