 The bad jog circuit in this video. We're gonna be going over a concept called contact racing now There are many different methods for jogging a circuit if you are inching a circuit or bumping a circuit You can use a control relay or you can use a selector switch And you can also use a two-position push button, which we'll discover in this video is not always the best way to go So here we have our basic jog circuit utilizing a two contact push button I'm talking about this jog push button right here. So we have our typical stop normally closed push button We have our start normally open push button. We have a coil. We have our overloads We have a holding contact that is associated with this M coil And then we have this two-position push button where right now it's in the normally closed position But if we press down on it, it'll make contact with the normally open contacts on that side And that can cause a problem which we'll discover later on in the video So going through the regular start sequence, we press the start button down We make contact power can get through to the M coil M coil energizes which in turn closes these normally open contacts This push button here is normally closed So it actually goes through there goes through the normally closed contacts and holds in the circuit So when we let go of that start the M coil will still stay energized and the motor will still stay running as We can see here the starts up But we have a parallel path going through and maintaining that M coil to keep it energized now. We need we're gonna press stop We go ahead and press stop and that deenergizes the entire circuit M coil Deenergizes M contacts open and nothing works because power can't get through the stop and Power also wants to stop button is up can't get through the start can't get through the normally open contacts and can't get through these normally open contacts So as you can see again can get through the stop now But gets to the start can't go gets across the jog can't go across the normally open contacts and cannot go across these normally open contacts as well Now what we'll do is we'll hit the jog and the whole purpose of a jog circuit is to momentarily Run a motor so you can bump it or you can just have it run for a moment as opposed to when we hit the start here This ran continually. We only want this to run as long as we're pushing down on the jog button So if you see here, we can get through it won't go through this start It won't go through the jog But it now will go through these normally open contacts that are closed by the switch and Energize the M coil one thing that's very important to note is M coil is energized These contacts will close because whatever this does it tells these guys what to do So energized closed however, it won't hold in because it gets to this point here And it's opened up with this switch with this push button which seems pretty ingenious and typically it will work Judging here if we let go of the button, and I'm in the halfway point here I've broken the circuit which will in turn de-energize this M coil which will open up these Contacts, but there's a problem called contact racing in the sense that This button here as it goes back up can sometimes beat it back up before the coil de-energizes Or these contacts open So for whatever reason this button this push button bounces back quicker than these contacts can open Then what'll happen is you notice here? I've got a complete path going all the way through and this M coil will energize again And so the jog is bounced back before these have opened which in turn keeps this energized Which could be a danger in the sense that if you're just trying to move the motor or inch the motor or bump the motor But do not want it to run continually then you can run into issues where with this jog set up It can bounce back and actually will run continually and I have actually physically seen it happen many many many times In our labs where I teach just to prove that this circuit I would say about 50% of the students that wire it up It works fine when they hit the jog it just jogs a button But the other 50% if they do it quick enough or they they kind of hit that button really quickly It bounces back and the motor keeps running which presents a danger Which is why we prefer to use a selector switch in the maintaining circuit or the use of a control relay