How should i connect my single phase induction motor to soft starter so that i can protect starting capacitor or soft starter's PCR from buring out?

Learn the NEC with Mike Holt now!


I have single phase 2hp induction motor and i want to control its inrush current using soft starter which gradually ramp up voltage. I want to know that how i can use it safely without any damage to pcr or capacitor? Should i need to remove capacitor or connecting soft starter to running winding only or something else????


Senior Member
Electrical worker
Tried to do this before , did not get through , especially if there is a centrifugal switch on the rotor shaft, perhaps if it is an induction start,induction run motor it may work, or perhaps a shaded pole. motor would not kick off on on intial start ,currents went high on the start transition and tripped cut off switch motor may have to be designed for soft starter or VFD.


Moderator, OTD
Staff member
San Francisco Bay Area, CA, USA
Electrical Engineer
Or just buy the soft starter designed for single phase motors.

View attachment 2571637
No NRTL listing though...

In a previous life working for a Soft Starter manufacturer, we tried like heck to develop a simple to implement Soft Start that would work for single phase cap-start motors. It was a failed experiment. It was a race to see if the harmonics caused by the SCR firing during ramping would damage the capacitor, before the capacitor charging current caused the SCRs to self-commutate and short themselves out. One or the other would always "win" after about a week.

Soft starters will work for PSC or Shaded Pole motors, but you rarely need them for machines that can use those types.

These Australian Soft Starts for Cap Start motors likely do something different with regard to keeping the caps out and creating a virtual phase shift some other way, but I don't know their secret sauce on that. But the connection diagram would indicate they are somehow separating the two conflicting elements.