Making & Breaking Current

There is no such "basic formulae" for the breaking capacity or for the making capacity.

The breaking capacity of a breaking device should be more than the maximum anticipated short circuit current at the location of the breaking device, which should be calculated in a systematic way, duly considering all the sources of fault current and the network impedances.

Once you have calculated the breaking capacity as above, IEC 60947-2 specifies a Multiplying Factor to arrive at the Making Capacity. The breaking capacity has to be multiplied with the multiplying factor to calculate the required making capacity. The multiplying factors are:

Brekaing Capacity Multiplying Factor

4.5 kA to 6 kA 1.5

6 kA to 10 kA 1.7

10kA to 20 kA 2.0

20 kA to 50 kA 2.1

Above 50 kA 2.2