If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

SPDT switch

Created by Karl Wendt.

Want to join the conversation?

Video transcript

OK, so we're going to take a look inside of the single pole, double throw lever switch. So we have one pole right here and two throws. And what that basically means is that we can connect to three different locations on this switch and control the power in two circuits. So we're going to take a little small watchmaker screwdriver and pry open the housing. OK, so this is the inside of our lever switch. You can see it's all taken apart for us. And there are two contacts here. There's one pole here and two throws. And so what that means is when the switch is open, it can let the power flow in one circuit. When it's closed, it can let the power flow in another circuit. Or it can just close that circuit. So you can see what happens is there's a little tiny plastic hammer here that pushes against the spring, so the lever causes the spring to push down on this copper contact. And that is switching between this side and this side. So the switch is basically opening and closing the circuit between this side and this side, and then between this side and this side. So if you watch carefully, you can see that little copper contact shifting up and down. I believe these pieces are made out of aluminum. It looks like this spring is spring steel. It looks like we have the lever here, which is probably nickel-plated steel, it looks like. And we have a copper contact that the spring is connected to. And I think the housing is made out of ABS. And again, that's an injection-molded housing. You can see that it's got these little spikes here that stick up. I'm not sure if you can see that too well, but there's little spikes there. And they basically go through the top of the housing here in these little tiny holes. So if we put this like this, that's how it goes. And those little tiny spikes will stick through those holes. And then what they'll do is they'll take a hot plate or a hot piece of steel and push it against those spikes that are sticking through. And they actually mush down like a mushroom on top of this and hold it in place. And so that's what the top of our single pole, double throw lever switch, how it's held in place. And again, that looks like an injection-molded piece as well. So again, when we push the lever switch, it switches between this contact. This contact is always connected, but it switches between these two contacts. So there's single pole-- this is the pole, and there's two throws. So you can see these two throws are there. And when the switch gets bumped, it switches between those throws.