 Anti-plugging with a zero speed switch. Anti-plugging is when you don't want a motor to suddenly go in reverse. You want to make sure that it has come to a complete stop before you have the motor go into a reverse situation. We're going to look at how we can utilize a zero speed switch which is attached to the shaft of the motor to make sure that the motor comes to stop first and then can be reversed. Here is our forward reverse circuit. There's a little bit of a difference compared to a typical forward reverse in the sense that we have here our zero speed switch. We can tell that because we've got this arrow that's kind of curved here. That tells us that this is a centrifugal switch which means that in forward it's going to spin and open up this switch or in reverse it's going to go the other way and open up this switch up here. You notice I've got the R meaning reverse the F meaning forward. The rest of the circuit is pretty standard. I've got a forward push button. I've got some electrical interlocks. I've got a mechanical interlock between the F coil and the reverse coil. I've got my forward interlocks down below and hold in contacts for both circuits. We're going to look to see what happens when we energize. We'll start with forward. Forward I press the forward button down that energizes the F coil which in turn will close the normally open contacts down here and open up my electrical interlock down here so that when I release forward I have a parallel path to carry through and keep the F going. Then we're going to look to see what happens with our centrifugal switch. In the forward position I let go. The push button bounces back to its position. It's being held in by its own hold in contacts. As it starts to move forward this starts to open up. Because of the centrifugal nature of the motor it starts to spin, opens the zero speed switch. I can come here and I can hit reverse as much as I want. It's going to be locked out by the F contact here anyways but I need to make sure that when I hit stop that this F the motor is no longer running in a forward direction before I go into a reverse. So let's hit the stop button. I hit the stop button which de-energizes F which sends this back to normally open and this back to normally closed. So the motor might still be spinning through some inertia in the forward direction which keeps this zero speed switch open. So again until this motor has stopped spinning and this now closes I can hit this reverse button as much as I want. The power can't get through until the motor itself has stopped spinning and this zero speed switch has closed. So it's locking it out until the motor stops. So I let go of the stop button. It bounces back to its normally closed position. Again as long as this motor is spinning in the forward direction through inertia I can hit this as often as I want. R will not energize because it's being held out. Now when I go ahead and hit reverse it will do the exact same thing it did in forward but in the opposite direction. So let's take a look at how this whole sequence works. I push down in the reverse button. R coil energizes. R contacts close. Holds in. R contact interlock opens up. The motor starts to spin in the reverse direction. I let go of the reverse button. It's being held in by itself with these R contacts. It's spinning in reverse. You notice up here my zero speed switch has opened up this side because of the centrifugal force which is opening up the reverse. I can sit here and hit forward. Power is not going to get through. It's being held out anyways by these interlocks but as is there's no way for forward to become energized. If I hit the stop switch that will deenergize R which will open up this R which will close this R. Those sets of contacts but I can sit there and hit this as much as I want. Nothing's going to happen but first off let's see what happens when this bounces back. My reverse button has gone back to its normally sorry my stop button has gone back to its normally closed position and I still can't get the forward to go because as long as the motor's spinning through some sort of inertia in the reverse direction this zero speed switch will stay open. The moment it stops spinning this zero speed switch will close and then I can go ahead and hit forward. So that is how we utilize a zero speed switch to prevent a motor from going the opposite direction until it has come to a complete stop in the direction it was going to in the first place.