 The difference between a three wire circuit and a two wire circuit is the fact that you can let go of a push button and the circuit will stay energized as opposed to a two wire circuit where you need to physically be holding a push button down or there needs to be some other pilot device holding that circuit closed. So in this video we're going to look through and see exactly what we mean by a three wire circuit. Here's our basic three wire circuit. So we have a stop button that is set of normally closed contacts, a start button which is normally open. We have our starter or our contactor so this is our coil. These are our overloads and this is our holding circuit. So let's see what happens when we don't have this holding circuit to this contactor here. So we've gotten rid of that holding circuit as we call it. So what we'll do is we'll press the start button down and we'll see what will happen to this coil here if it will energize or not. As we push this down, this coil energizes because we see here we have a complete circuit or a path through where this coil can energize. Go through these normally closed contacts that are our overloads and through which completes the circuit. So as long as this button is pressed down, this will stay energized. The problem is when we let go of the push button, as often push buttons have our spring loaded, this will pop back up into the normally open position and the coil will de-energize. So what we need to do is we need to put in the holding circuit below the start. In fact, it's going to be in parallel with the start and then we'll see what happens with that. So we have our set of holding contacts which are also sometimes called two-three contacts or auxiliary contacts or sealant contacts. There's a bunch of plethora of different names for them. Now what we need to know is that when this coil energizes, this coil is physically attached to these contacts and they're normally open so that when this energizes, these contacts will close. So when we press the start button down, we should get a complete path all the way through which will energize our coil like it was when it was in a two-wire configuration. But what will happen now is these sets of contacts here will close. Which is exactly what happened. We have a through path here, and energizes. These contacts here are physically attached to this coil so they will close. Now what will happen now is that when this one goes up before when we had the two-wire configuration, it cut off the circuit to M and M de-energized. Now what is happening is these normally closed contacts are in series now with the M so it holds in. So this coil here is in fact holding itself in. So let's see what happens when we get rid of this start button. So we have a parallel path around the start. Yeah, it's in the normally open position, but these contacts are being held closed by the energized M coil. The only way to shut this off is to somehow break this whole circuit up. That would be to remove the contacts which is not practical or to push down on this normally closed stop button. By pressing down on the normally closed stop button, we open the circuit then the current cannot get through to keep that coil energized and everything shuts off. M de-energizes. When M de-energizes, it is physically attached to these contacts. It's the boss so it tells the contacts to open back to their normally open position and the circuit ends up back as it was. And there we have it. So it's a de-energized circuit. Now this is a circuit that is called low voltage protection and the fact that if we lose voltage here, this coil de-energizes and then the circuit will have to physically be restarted with this start button or some sort of automatic function. But as we see it, it needs to be restarted. It won't start automatically, which is considered to be low voltage protection or LVP.