If you want to get more technical, flick a meter on ohms across the windings and measure the resistance. This sets the highest the current can ever be, however, there is also some inductance, which is largely dominated by the air gap in the magnetic path, that takes the edge off that current peak a bit Then there is the back EMF that rises generator-like as the motor picks  up speed so the current that flows is the voltage difference between supply and generated divided by the winding impedance. The ramp up time can be estimated by listening to a start up, and is however long it takes the motor note to stabilize - it is a strong function of load - hence load lifting (line unloading) valves on large compressors to get the thing started before the back pressure and the torque rises to the final value.

The figures you quote will be about right for a motor of a few HP starting under constant load, but be aware such things can be very variable indeed. 

Mike.

If you want to get more technical, flick a meter on ohms across the windings and measure the resistance. This sets the highest the current can ever be, however, there is also some inductance, which is largely dominated by the air gap in the magnetic path, that takes the edge off that current peak a bit Then there is the back EMF that rises generator-like as the motor picks  up speed so the current that flows is the voltage difference between supply and generated divided by the winding impedance. The ramp up time can be estimated by listening to a start up, and is however long it takes the motor note to stabilize - it is a strong function of load - hence load lifting (line unloading) valves on large compressors to get the thing started before the back pressure and the torque rises to the final value.

The figures you quote will be about right for a motor of a few HP starting under constant load, but be aware such things can be very variable indeed. 

Mike.

If the motor was installed this would be an option but we are at design stage and of course nobody has any details of what motor will be used. We are going to have 4 motors installed on one switchboard with staggered start so only one more is starting at a time but I want to be sure the upstream MCCB won't trip. In all likelihood it will be fine as we will specify the MCCB with adjustable overload, short circuit and instantaneous trip. My main concern was the overload trip time being too short so it sees the starting current.