 A sump circuit is a pit or a hollow that is meant to collect some sort of liquid. And we're going to be looking at how a sump control circuit works in this video. Here we have a very basic sump control circuit. We have a three position selector switch. We would have a hand in this position would be off and down in this position it would be auto. In hand the motor or the pump will be running automatically and will continue to run regardless of what the floats do. So what we're going to do is concentrate specifically on this part of the circuit here, the automatic part. You notice we have these two floats which are in a normally open position. Now you'll notice that I have one float here and one float here. I also have a drawing of the actual sump or the pit over here. And so these floats will be associated with these floats as well. So what we're going to do is we're going to start filling this tank and we'll see what happens to these floats in the control circuit. So we've seen water rise up and has that happened that bottom float or low level float rose up and then it closed, which would mean that this one right here is our low level float. Now we don't want the motor to start right away once this goes up because you'll never end up being able to fill the sump up. It'll just get to this one point and then drain, get to this one point and drain. What we're looking for is to get the maximum efficiency out of this sump. So we're going to wait until it gets all the way to the top, which is why we have this high level float. So our next step is to see what happens when this water here raises to the high level. Now that our level is raised, the water has started from the bottom, moved up and kicked up our low level float. And now we've gone up to the top. So we've reached the top. The high level float is engaged as well. When that happens, we can flow down through here. Our starter engages, goes through the overloads. And when the starter engages, the normally closed or normally open contacts end up held closed through this and away we go. And so the motor starts to pump and as the motor pumps, it starts to drain the water out of the tank or out of the pit. So we'll see what happens next. So here we've seen that as this began to pump, that the level has dropped, which means that the high level float has dropped down, the high level float in the control circuit has dropped down, but we still want this water to drain. So what we need to do is to have it continue on. So we do that by having these holding contacts here. So again, the current can come down through the holding contacts up and keep that energized and continue to pump down throughout the circuit until this low level switch drops out. And then we'll take a look to see what happens when that occurs. And as we now see, once our low level switch drops down, once the level is dropped below the low level switch and it drops out, that basically kills the whole circuit. This pump de-energizes, the starter de-energizes, which stops the pump. It opens the normally open contacts back to its regular state. These have now dropped out and the reservoir or the tank itself or the pit or whatever you want to call it, whatever is collecting the liquid is fairly empty. And again, then the process will start again as the level rises, as the low level switch closes, that won't engage until it hits both the low level and high level. And then as the high level drops out, it will continue to run until the low level kicks it out. One thing I'd like to quickly note is that this circuit is actually a low voltage release circuit, not low voltage protection. Because a low voltage protection circuit, what will happen is when the power drops out, the M drops out and you'll have to physically go back and push a button or get something to start this M again. But what will happen here in the sump circuit is if both these switches are high, if this tank is both, is all the way full, power goes out and then the power comes back on, the pump will stop or start running right away. So we have to be aware that this circuit here at a sump circuit is a low voltage release circuit and not a low voltage protection circuit.