 When dealing with time delay relays, we have two kinds. There are the on delay and the off delay. This video will focus mostly on the on delay principles and how they can be used in sequence control for motor control. Now an on delay relay is like any other relay. It will have a coil and it will have a set of contacts. Now the difference is not only does it have a set of instantaneous contacts. So here I have a normally open set of contacts, a normally closed set of contacts and what I mean by instantaneous is when this relay or coil energizes, these contacts will close instantly and these contacts will open instantly. The difference is these contacts here I have a normally open time to close and I have a normally closed time to open. So let's take a look at exactly how that plays out. So I've pushed a button, I've energized this coil, this TDR, time delay relay and it's got a timing of five seconds. The moment I press that button and this energizes, these contacts here, the ones that were normally open become normally closed and the ones that were normally closed become normally open. They don't pay attention to the time at all. The time means nothing to them, they're just instantaneous, they do what they're supposed to do right away. What happens though is you notice here that this coils energized but this normally open time to close stays open and this normally closed times to open stays closed. So it holds in those positions until the relay times out. So it counts to five, one, two, three, four, five and then this will close and this will open. So there we go, after five seconds this will become closed, this will become open. So again, the sequence of events are this coil becomes energized, these will do what they're supposed to instantly ignoring the time but after the coil has been energized for five seconds these contacts will close and these contacts will open. The moment I de-energize the contacts everything falls back to its original state. So TDR is de-energized, those become back to normally open, those become normally closed. This drops out to normally open time to close and this drops back to normally closed time to open. So with on delay relays the timing for these sets of contacts down here begin when this is energized, it starts to count and then these contacts will do what they're supposed to do. Now let's take a look at how this would play out in an actual circuit. Here we have a very simple circuit and it's for sequencing. Let's say for some reason we don't want M coil and M2 coil to energize at the same time meaning that we don't want M motor M to start at the same time M2 does. Perhaps there's too much of an inrush current for whatever reason. So we want some sort of time delay, we don't want M2 to start right away, we want it to start five seconds after M starts. So what we're gonna do here is we're gonna follow through the sequence of events. I go ahead and I press the start button which will energize M coil, which will close M contacts which will also energize the time relay here because it is in parallel with the coil. So these two are energized. Now you'll see when I let my finger off the start button these two will stay energized. I release the start and this coil and this coil stay energized due to the fact that I have a hold in seal in or auxiliary contact there that provides a parallel path around this open switch to keep M energized and TR energized. Now we noticed that down here we have a normally open time to close contacts here. They stay open for five seconds. So I press this button, this energizes, this energizes and then five seconds later this normally open time to close contact will close and M two will start. So again, the sequence press start, M energizes, contacts close, TR energizes at the same time, five seconds later this counts for five seconds then this set of contacts closes and M two starts. So M one starts instantly, M two starts five seconds later. When you hit the stop button basically everything drops back to its original state. I have no through path to here which will de-energize M which will open those contacts, de-energize TR which will open those contacts, M two will de-energize and everything goes back to its original state. The stop button snaps back to its original position and we're good to go for another sequence later on should we want to go ahead and start the motor. So again, the timing begins on these contacts the moment that this relay becomes energized.