When the relay is energized, it opens the one that was normally closed and closes the one that was normally open. So when it's de-energized, what happens if the blower relay isn't kicked in because we don't have a G call high voltage heat strips come on these clothes, we have current flowing through here. Well now it has a path to the blower. It's going to bring the blower on and that's going to be carried by these heat strip, contactors or C currents or whatever you have that's actually rated for high high enough amperage to do the job.

So this is safe if this blower relay kicks in. So if we get a G call, it's fine same thing will happen. This will now go from normally close to normally open. So this is if it's energized it'll switch positions, and now this will go closed.

It'll bring the blower on, but it won't back feed the heat strips. It won't allow it to work improperly, and so that's all just a function of taking this relay and turning it upside down and thinking of it differently and not just working from left to right. Once you start to think in that way, not just having to use it in the way that you're used to using it now, all of a sudden, you can use that relay in the opposite way and connect the common side. What we call common or terminal one to the load rather than the power supply, and it gives us the ability to create this unique interlocked.

So this is a common problem. When people are working on fan, coils or air handlers, it's actually fairly common mistake and it happens with the best of intentions by technicians who think they understand relays and probably do but just make silly mistake. So basic principle: when heat strips run, electric heat runs. We want the blower to run as well similar to the way that an integrated circuit board does on a gas furnace where, when you get a double, you call so white low voltage.

It brings on the gas and then the integrated circuit board brings on the blower. Well, with heat strips whenever the heat strips are on, you want the blower to be on, but it's the G call the G terminal from the thermostat that controls the blower. So just in case you don't have a G call from the thermostat and you still have a ww2 call bringing on your heat strips. You want that blower to come on, and so this is a common thing.

If you look at this diagram from carrier, this is an example of a system like this, and you have a blower relay which is very similar to this blower relay right here. That's got normally closed and normally open contacts, and you need to what we call interlock. This so that way, the blower will come on when the heat strips are on, but we cannot have the blower relay bringing on the heat strips, because it's not rated for that current. Nothing in that blower relay can bring on the heat strips and we don't want it to accidentally bring on the heat strips when the blower is on.

For any reason, no matter what we do, we only want this to work. One direction, not the other and that's where it gets tricky, so let's show some of the basic components that are used when you're working with heat strips blowers, you're, not gon na see these commonly in gas furnaces. This is mostly a fan, coil air handler thing, but there may be some applications where you see relays and other electrical situations, it's good to understand them, even if you don't work on many of these types of systems. So, let's start over here.

This is a 9370 relay. It's a very simple relay. If you look on the side, it'll give you a lot of information about it. We've got a 24 volt coil, you can see 9370 that's listed there and then it actually shows what every terminal does over here.

On this side - and so you can actually see here that the coil is our contacts 1 and 3, which makes sense they're kind of down here by themselves. So if you were going to use this as a blow relay, you would connect your green, which is your 24 volt blower, call to one side generally one, because that's sort of the way we like to think of it reading from left to right, and then your Common to terminal number three, but it wouldn't matter which way you did it polarity, doesn't matter here and then we have two four five and six, but you can see, six is just a dummy. It doesn't actually do anything. So if we look on this right here, you can see that four and six are actually tied together.

So four and six are now the same thing. So four is tied to six just for the purpose of making the internal connections on the relay and our normally closed contacts are between five and four and our normally open contacts are between two and four on this relay. That's a very simple, very inexpensive relay. When you go to the next relay up, this is actually a double pole, double throw relay, and so you actually have double throws where it can go normally open normally closed, but then it has two sets of them.

We have our coil down here in the bottom, which is quite evident on the 9340, so this is where we would connect if this was being used as a blow relay and by the way, with what we're talking about today, blowers and heat strips you could not Use this for your heat strips because it's only rated at 15 amps this one here is rated at thirteen point: eight full load amps, so you could not use that, so these relays are generally rated for only fifteen amps and depending on the exact application. That's about what they're gon na do for you, and so you can't use these for heat strips a five kilowatt heat strip at 240. Volts draws right around 20 amps, so not something you can use for a heat strip and that's actually one of the big mistakes is accidentally running hike too high a current through these contacts and then melting and damaging. But this diagram makes it really easy.

You can see between 1 & 2 is normally closed. Between 1 & 3 is normally open. Between 4 & 5 is normally closed in between 4 & 6 is normally open, blue tentacle. These are common points and we generally think in this direction, though you're gon na see that, in the case of using this or even the 9370, to connect with a blower interlock, we actually have to kind of think of it the opposite direction.

If we want to keep it running in this same kind of left-to-right way that we're used to thinking of we're actually going to connect our L, 1 2 3, our Heat strips 2 2 and our blower 2 1. If we use this set of points or if we're using this set of contacts here, when I say points, points and contacts are kind of synonyms. If we were using this set of contacts here, we would feed l1 into six connect on our heat strip side to five for our analog purposes. Only and then our four to our blower and again, we can't run a heat strip current through these relays, because they're not rated for it same thing, is true.

With this carrier relay we've got here, you can see common, so that would be you know, kind of equivalent to our point one on our 93 forty and then we have our normally closed and our normally open contact, and so actually we're going to connect our common To our blower and if you're used to these, you know that's what's connected, there are normally open, is going to be connected to our power, supply or l1 side, and then normally close is what's going to go to our heat strip interlock, and then we have our Relays that we can use relays contactors that we can use for powering the heat strips themselves because they have that rating. This is a sequencer stack, sequencer, which stages on and off, and the reason it does. That is because, rather than using a magnet, it uses a heater and it activates or deactivates a little bimetallic disks in here, and so they always have a slight time delay to turn on and turn off. The time delay is greater on the top, because it's further away from the heat source, so these little biotech discs actually snap open and closed based on that heat, that's generated inside the sequencer and then a contactor.

This is just a very simple, 40 amp contactor, which is another thing we can use for the purposes of heat strips and, in fact, is what's used on this set of Goodman heat strips that you see right here, but again, the goal and what I'm going to Show you today is how to ensure that when the heat strips come on the blower comes on, but not vice versa. We don't want the heat strips to come on with the blower. The heat strip, contact or sequencer can handle blower amperage, but not the other way around these little relays here cannot handle heat strip amperage this one as well. So we have to make sure that we wire them again according to the manufacturers, are going to have wiring diagrams, but I see a lot of technicians when they go to maybe use an aftermarket part.

They make a mistake in this wiring. Look at these heat strips. You can see here, these are our power feeds that would come into our contactor and then coming out of our contactor. That feeds our heat strips now.

This set of heat strips is a 7 kW, so each one of these coils is three and a half kilowatts. Apiece, let's talk about everything that you're seeing here, because sometimes it might look a little confusing. It's actually very simple. So what's happening is we're breaking both sides of power with this contactor, so each side of power is breaking one leg, one on the L one side and often that's where we think of going in because we read left to right.

So we think of the left as going in, although an alternating current it doesn't matter, and so let's imagine that this here is our L, one going in it feeds in here which these are our fusible links, so those break because of high temperature. It will shut down the heat strips and those would have to actually be replaced, comes out of that and goes into our heat strips travels through our heat strips comes out the other side and then goes through a thermal limits. These are just snap action, bimetallic discs, so if these overheat, these will shut off the heat strips, but they will reset. So these are resetting time, and then it comes back goes to the L to side.

Assuming this is the L to side again haven't looked at the diagram, but it doesn't really matter and then goes back to the power supply on the other side. So heat strips are very simple: they're resistive. All we have to do is just provide l1 and l2 and make sure that they don't overheat, which that's a big part of making sure that blower comes on whenever they are on. So, whenever we have that w call which again this is gon na, be our W call so white 24 volts to one side back to common on the other.

When we get that 24 volt call these contacts pull in, and that brings on your heat strips. So when we look at a relay, we tend to think from left to right because that's how it's drawn and that's how we read from left to right. So one two three. We have normally closed from here to here and normally open from here to here, and we would also tend to call this one terminal, a common, that's just typically how we would think about it.

It's the common point in between these two sets of contacts, but when we try to apply a relay wiring it up in that way, it gets a little confusing. It's a mistake that we often make so I'm gon na go ahead and draw this real, quick and fast forward enjoy the music. While I make this terrible drawing all right, so we have 240 volts AC between l1 and l2, so we're gon na draw our loads in between we're, not gon na. Do the low voltage here, because this is a high voltage interlock, not a low voltage interlock.

So, no matter why the heat strips are coming on, if they're coming on, because, obviously for them to come on, they have to have high voltage applied all the way across on l1 and l2. We want it to bring on the blower, so I'm gon na write HC for heating contactor here all right, so here's our blower - and this is our blower relay so we'll just write fr for fan relay something like that. That's a common nomenclature for that! So now, if we give a G call, it closes the switch so low-voltage 24-volt G call energizes the coil, a contactor energizes, the coil of the relay shuts the relay contacts brings on the blower heat relay closes both of these brings on the heat strips. The problem is, we've got no interlocks, so we want this blower to come on when the heat strips are running.

So what do we do? Well, first thing the guys will think is well. This is simple. All we do is we just connect a wire from here to here. Obviously, that's incorrect, because what will happen is now anytime.

Even the blower is on it's gon na back feed and bring on the heat strip, so that doesn't work. So next they pull up in a relay and the relays oriented like this - oh my god and redraw it here. So it's a little bit easier. So the relays oriented something like this, where you have your common terminal, which on the 9340 is listed as number one, and then we have our number two is normally closed point from number one.

So we'll draw it here. So this is B terminal number two and then we're gon na have a normally open switch here and that would be terminal number three and that works just fine because it closes the switch brings on the blower. But still we've got no interlock. So, where do we connect this number to terminal in order when we have it wired like this? In order to get this to work? Well, it doesn't matter where we connect it.

It's not gon na work. If we connect this number to here. Well, what's gon na happen, these trips are gon na run 24 hours because it's gon na feed through the relay. So not only is it gon na melt, the relay and the relay wires because of the current that heat strips draw, which is higher current generally about 20 amps, but it's also going to ruin the relay and the process and the heat strips are gon na run.

All the time you're gon na have a high power bill, so this doesn't work. So where can we connect this normally closed relay in order to fix this? If we connect it out here, that does nothing for us if we connect it on the other side of the heat strips it's a dead short, no matter what we do when we wear it in this way, it's a problem, and it's because we're looking at the Relay right side up and we're looking at it from left to right, imagining that we have to hook common to l1, and we don't have to do that at all. All we got to do is turn the relay upside down, so instead we connect power to three. We connect blower to what we would call common or one.

That's are normally open contacts and now what do we do? Well now one is connected normally closed right now we can connect that terminal right here, number two. So that's how we connect that now. How does this work? Well? Because, when the relay is energized, it opens the one that was normally closed and closes the one that was normally open. So when it's de-energized, what happens if the blower relay isn't kicked in? Because we don't have a G call high-voltage heat strips come on these clothes, we have current flowing through here.

Well now it has a path to the blower. It's going to bring the blower on and that's gon na, be carried by these heat strip, contactors or C currents or whatever you have that's actually rated for high high enough amperage to do the job. So this is safe if this blower relay kicks in. So if we get a G call, it's fine same thing will happen.

This will now go from normally close to normally open. So this is if it's energized it'll switch positions, and now this will go closed. It'll bring the blower on, but it won't back feed the heat strips. It won't allow it to work improperly, and so that's all just a function of taking this relay and turning it upside down and thinking of it differently and not just working from left to right.

Once you start to think in that way, not just having to use it in the way that you're used to using it now, all of a sudden, you can use that relay in the opposite way and connect the common side. What we call common or Terminal one to the load rather than the power supply, and it gives us the ability to create this unique interlock and that's pretty much the standard way that this has been done in air handlers and fan coils for essentially ever it's the Way that it's done in this carrier diagram that you see right here, if you, if you look you'll notice, that the common side of this relay in this diagram is connected to the blower not to the power supply. The power supply is connected to the other side. On the normally open contacts so again just to show it the way that it really is clean this up a little bit just so you leave me and a good screen and don't get confused.

We're gon na connect the blower to our common terminal, we're going to connect from here to our normally closed contacts. Normally closed contacts go on the load side of the heat strip, contactor or sequencer, and then we have our normally open contacts. So, in the case of the carrier blower board, this would be common, normally open, normally closed. Just that simple.

So hopefully that helps, and mostly what I'm wanting you to see is get a better sense of relays how they work diagrams, how they work, but also thinking outside of the box and realizing everything doesn't always have to go from a light right to left. Even though relays are generally used where the power supply connects to the common or that one terminal on the left side, you don't have to necessarily use them in that way, and in this case you actually cannot use them. That way. Thanks for watching.

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