How to calculate starting current in a motor

**JesseDC** · 05-Jul-22, 05:19 PM

Hey all
How do you calculate the starting current for iec motors, I can't find a clear answer, but nema motor manufacturers have clear guidelines for their motors so there must be some sort of method

**GCE** · 06-Jul-22, 05:32 AM

Manufactures specifications/charts will be the only way.

Each make/size has a different ratio and the reactance will need to be calculated for which you will also require the specifications

What size motor are you talking about ?

General start up is 6 times full load as a thumb suck

**AndyD** · 13-Jul-22, 01:44 PM

We always measure the inrush / start current using a suitable clamp meter, unfortunately a cheap clamp meter can't give an accurate measurement of this. The inrush current can vary greatly with voltage so a small motor may have an inrush current of 4 times the run current at 230v but when the same motor starts up after loadshedding when the voltage is 205v it might have a start current 20% higher.

Manufacturers may publish data on start current ranges but these figures will often be with the motor at full load or zero load. In the real world the actual load will be somewhere in between so I always recommend taking a live measurement.