MCB Vs MCCB instantaneous Pick up

The more complex MCCBs allow you to adjust both the near instant and normal pcik up values, and in some cases the time delay as well. Otherwise, browse the maker's data.

But the useful range for real applications often ends up being   fairly similar to something between the B and C type breakers. This is not too surprising, as the sort of cable requirements for voltage drop mean that if you set the instant trip to a lot more say - 20 times the nominal current, then you would never operate (or you need a massively oversized supply). ( e.g.  the same cable resistance that gives 5% voltage drop at nominal full load sort of maps to a 20:1 ratio of short circuit to nominal current and a 10% drop to 10:1 ratio etc.) Equally co-ordination with the inrush performance of fuses, breakers etc down stream often  means that a ratio  much less than 3:1 is likely to lead to uncertainly about what will trip first.

And then when Zs is a bit uncertain, there may be an extra 'shunt trip' - usually a mains voltage or 24V solenoid add-on that forces a trip, that may be wired to be operated by an earth leakage monitor, or indeed any number of other alarm devices.
Mike.

The more complex MCCBs allow you to adjust both the near instant and normal pcik up values, and in some cases the time delay as well. Otherwise, browse the maker's data.

But the useful range for real applications often ends up being   fairly similar to something between the B and C type breakers. This is not too surprising, as the sort of cable requirements for voltage drop mean that if you set the instant trip to a lot more say - 20 times the nominal current, then you would never operate (or you need a massively oversized supply). ( e.g.  the same cable resistance that gives 5% voltage drop at nominal full load sort of maps to a 20:1 ratio of short circuit to nominal current and a 10% drop to 10:1 ratio etc.) Equally co-ordination with the inrush performance of fuses, breakers etc down stream often  means that a ratio  much less than 3:1 is likely to lead to uncertainly about what will trip first.

And then when Zs is a bit uncertain, there may be an extra 'shunt trip' - usually a mains voltage or 24V solenoid add-on that forces a trip, that may be wired to be operated by an earth leakage monitor, or indeed any number of other alarm devices.
Mike.