Soft Starter

8–170 A and 200–600 V

ISA-A Analogue Soft Starter with motor protection and built-in bypass

Advantages at a glance

  • Soft start and soft stop
  • Current limit
  • Build-in motor protection
  • Build-in bypass
  • Start/stop by dry contact
  • Compact, small foot print
  • Aluminum housing
  • Integrated input voltage monitoring


For full view please move the table horizontally if necessary.
Starter Type kW at 400 V Width (mm) Height (mm) Depth (mm) Weight (kg)
ISA-A 8 4 120 232 105 2.6
ISA-A 17 7.5 120 232 105 2.6
ISA-A 31 15 120 232 105 2.6
ISA-A 44 22 120 232 105 2.6
ISA-A 58 30 129 275 185 5.0
ISA-A 72 37 129 275 185 5.0
ISA-A 85 45 129 380 185 8.4
ISA-A 105 55 129 380 185 8.4
ISA-A 145 75 172 380 195 11.8
ISA-A 170 90 172 380 195 11.8


Current limit

The voltage increases linearly from the “Initial Voltage“ pre selected point. If the adjusted “Current Limit” is reached, the voltage will stop ramping and remain at its level until the current is reduced below the adjusted “Current Limit“ level. In that case ramp up time is prolonged until the current has reduced below “Current Limit” level 

Soft starter output voltage

Although the current is limited the motor provides suitable torque to accelerate the driven load and reach “End of acceleration”. If the motor torque does not exceed the load torque the motor will not start. In the so rare cases severe damages might occur to the motor and starter.

Motor start measured with an oscilloscope
(Ch1, voltage; Ch2-4 current L1 – L3)

The oscillogram shows, the soft starter providing a smooth and stepless current and voltage ramp to the motor. The voltage ramps up until “Current Limit” is reached. After the motor is at nominal speed, the current will decrease, to the nominal motor current.


Internal bypass

  • This reliable components bypass the power electronics after the motor is at speed.
  • In addition the starters provide an auxiliary contact, allowing signaling of a successful motor start.Attention! Many of our competitors call these auxiliary relays “a bypass contact”!
  • The bypass function reduces the heat dissipation and eliminates the EMC load of the system.


The analogue product line provides simple potentiometer settings for all the parameters:

  • Familiar setting, similar to standard overload relays
  • Easy commissioning
  • Prior knowledge is not necessary
  • Status display via LEDs
  • ISA-A include motor protection functions