Frequency drive (VFD)
Three-Wire Start / Stop
What is three-wire start/stop on a frequency drive?
It is a connection in which the frequency drive is run with start and stop buttons. When the start button is pressed once, the drive remembers the run command; the seal-in is done inside the drive, not with a contactor. Pressing the stop button stops the motor.
Where is it used?
It is used on machines the operator starts with a button, in plants used to classic start-stop control and wherever the motor must not start by itself when power returns.
Wiring and parameters
The start button (NO) goes to one digital input and the stop button (NC) to another, and the inputs' functions are assigned with parameters. Here the logic of the classic seal-in circuit is carried out by the drive's software.
What to watch out for
Wiring the stop button as NC matters: if the stop cable breaks, the motor stops, so a fault stays on the safe side.
Parts used
- Motor 3~
- M1
Run it in the simulator.
This circuit is ready in the CoilPath library. Open it, press the buttons and follow the current. It also comes with a wiring view and a panel layout.