Direct-on-line start in star or in delta wiring (Y or Δ)
In star wiring, the 3 winding phases of the motor are combined to form the so-called star point. With a supply voltage of 400 V, the phase voltage (voltage between the line conductors) is about 230 V each.
In delta wiring, the ends of the 3 winding phases are combined and connected to the individual phases. With a supply voltage of 400 V, the phase voltage is 400 V each.
A motor that is approved for direct-on-line start in star and in delta wiring allows connection to two different voltage sources. The voltage in star wiring is √3 higher than in delta wiring, i.e.
- a motor specified as 40S has a nominal voltage of 400 V in star wiring or 400 V/√3 = 230 V in delta wiring,
- a motor specified as 70S has a nominal voltage of approx. 690 V in star wiring or 690 V/√3 = 400 V delta wiring.
Switching between star and delta wiring is possible, provided the motor is suitable. However, the arrangement of the wiring must be changed - i.e. the motor cannot switch during the start, in contrast to a star-delta start (Star-delta start (Y/Δ)). Special voltage motors are available for deviating nominal voltages.