 Low voltage release versus low voltage protection LVR versus LVP Let's first look at what is called a two-wire circuit or what will generally be known as a low voltage release circuit Here we have a thermostat that will is normally open. We have our contactor here, which will be a coil M We have our three overload contacts normally closed during that. It's a three phase motor Now power can come through and get to this node, but won't jump across until this is closed This will start to close as the room heats up So as this room heats up here this contact here this thermostat will start to close when the room gets too warm Whatever you've set your thermostat to then M will energize So I'm energizes let's say this is an exhaust fan or some sort of cooling or AC unit So the thermostat the room is hot so the thermostat closes The coil pulls in energizes which will in turn turn on the motor and away we go now Let's say that power drops out for whatever reason Let's say hydro or some sort of utility goes down and or breaker trips We lose power to this but the room is still warm enough that this thermostat is going to be held closed So the big thing that happens here is this M is de-energized However, this thermostat this temperature switch stays in the closed position because of the conditions of the room So what'll happen is power will be restored to the circuit whether it's just resetting a breaker or Power being restored from a utility this coil will energize So the M coil energizes and then the AC unit turns on or the exhaust fan goes on automatically upon re-energization or upon the power being returned to the circuit So we call this circuit this particular circuit a low voltage release and there is a danger in it There's safety issues that you have to take into account It is a circuit that is used and say sump circuits or in exhaust fan circuits where you want them to Automatically turn back on when there's power restored to the circuit But you need to be aware that this is a low voltage release So if you are working on say if you're working on the motor that is associated with this coil You need to be aware that you need to make sure that you open it up and lock it out Which you should be doing anyways But just be aware that when power gets restored this will energize because of the condition of the room So that's low voltage release Here we have a three wire circuit and in this situation We have a stop button and a start button stop being normally closed start being normally open We have a M coil We have again have our three overload contacts and we have M contacts here Which are associated with this M coil when this energizes these clothes So we'll push down on the start M coil will energize and contacts will close because when this pulls in these clothes and Power can go all the way through and so M is energized. We'll let go of the start button Which will bounce back to its original normally open position But it will be held in this position This M coil will stay energized because of these holding contacts or ceiling contacts Because it now has a parallel path around that start to keep M energized So it basically holds itself in Now when power is gone say again with the utilities or a breaker trips or for whatever reason power is taken away from this circuit Then what will happen is M will de-energize when M de-energizes These contacts the ceiling contacts will open up keep in mind that this start button was already in the normally open position So let's say that power is restored to the circuit What will happen is power can come to this node here And it can't get across the start switch and it will come to the normally open and it can't get across the normally open contact So in order for us to start the circuit we need to press down on the start button once again Which will in turn energize the M coil which will pull in the normally closed Sorry normally open contacts and again We will have the seal itself in so that when we let go of the start button It will have a parallel path to keep M energized This circuit here is called low voltage protection So a low voltage protection circuit needs to be reset when power is returned to the circuit So that's the difference between low voltage release and low voltage protection low voltage release or a two-wire circuit Will automatically start up upon power or low voltage being our power returning and A low voltage protection circuit needs to be reset So the three wire circuit needs to have somebody go out and press that start button Now I'm going to show you one more Example of a low voltage release circuit because it commonly can be thought of as a low voltage protection But that would be a mistake Now this is a sump circuit and you can watch the video on sump circuits and see exactly how they work But what trips people up in here is you see these holding contacts here Often people will see the holding contacts and assume that this is a low voltage protection circuit, which it is not it is low voltage release So let's take a look at what happens when we get these two float switches in their closed positions So both float switches are up M coil is energized This set of contacts is closed and away we go So these guys will go and keep it energized as we see the circuit going through Now let's say that the power is gone So no more power here, which means that this will de-energize and that this set of contacts will open However, when power is returned you notice here We still have a path these floats as long as that level is up these floats are both being held closed so it will has a complete path to get to the M and De-energize that so when power is returned we'll see M fire up And again as power is returned to our circuit M coil is energized and M contacts are basically Basically M contacts are closed and away we go the circuit works Basically what this set of contacts does in a sump circuit or a reservoir circuit is it bypasses a float switch So it doesn't hold the switch closed Sorry, it doesn't hold the switch or circuit open It actually just is there to bypass a certain Situation when we have a float and in order to understand how that works You should watch either the sump circuit video or the reservoir circuit video So again, remember that not all low voltage release circuits look the same and if there's a set of holding contacts there They're not necessarily going to make the circuit a low voltage protection circuit