All right in this quick video, i want to deal with a really common misconception in the field. Two words they get confused all the time. I've talked about it a lot already, but i want to make it very simple, short and open. An open circuit is a case where you have something broken generally speaking, so you'd have a wire and that wire has a break in it.

So it's not making contact in order for anything to be energized, whether it's something simple like a you know, a contact or even a compressor. You have to have a path through that load that allows electrons to move through it and when that path is broken, whether it's by design in the case of a switch, you know, contactor relay something like that. That's opening the circuit on purpose or in the case of a broken wire or a you know, burned up, disconnect or a terminal. That's come unhooked or whatever.

That causes something to not happen. That's supposed to be happening, so you walk up and the thermostat's calling for cooling, but the contactor's not pulling in that's a case of an open circuit. Now, where it gets confusing, is that a lot of people use the term short, which is something totally different. As a universal term for electrical problems, it is not a short, is a specific problem.

It's a specific fault and a short specifically is when you have a case where electrons are able to take a shorter path. They're able to bypass the load, therefore resulting in lower resistance in most cases in the circuit, which often leads to high current, i'm going to say that again, most short circuits result in lower resistance which results in higher current and that higher current is what trips a Breaker below is a fuse. A breaker fuse doesn't know why the current's high it just knows it is high and that's why it trips or blows so when you see a trip, breaker or blown fuse. Now that is an open circuit, because the breaker has tripped or the fuse has blown, but that open circuit, open circuit, breaker, open fuse happened because of a short circuit in some cases.

Now not all that's not the only reason that a fuse blows or a breaker trips, but it is one very common reason. So, let's think about it simply with a thermostat wire, this thermostat wire each one of these colors, which are just you know, colors, are just there as a reference so that you can connect them to the right points on the other end. But of course, there should be a path, for example, from one end of this yellow wire to the other end of this yellow wire. There should be a path here and it's this should have no other paths to anything else, because it's just one side and the other.

So if you imagine one of these sides is your thermostat and the other side is your furnace, for example, and so, if i were looking for a short circuit, what i would be checking for is this yellow wire connected to any of these other conductors when it Shouldn't be, or is this yellow wire connected to say ground, for example, the grounding in your house all connects back to the neutral terminal on your panel, which allows a path, and so that path can allow current to travel through this wire to ground and then back To neutral and that results in a high current condition too many electrons when you have too many electrons moving it's because the circuit doesn't have enough resistance. If i'm going to test to see if this wire is open, what would i do well if i want to see if it's open, i want to see if it has a break in it. So if it has a break in it, then there will not be a path across this yellow wire. The problem is, is that, with my electrical meter, i often don't have access to both sides of this wire so that i could easily take probes and measure from here to here to see if there's a path with an ohmmeter or a multimeter.

So what do i do instead? Well, if i'm checking for an open circuit, i would disconnect all the wires on one end. I would strip back the ends and connect them all together. Now i can wring out all of these wires to each other and they should all have continuity, which means a very low resistance. That's you know, use the ringer feature on your meter and you go through, and you would see that all of these have a path to one another.

Unless one of them is broken and if one of them is broken, then that particular one isn't going to ring out: it's not going to show continuity. So that's how you would check for an open and you can do the same thing to check for opens and high voltage electrical. You could take a a circuit from one end to the other tie. The two ends together.

Isolate them safely, obviously, and then go on the other end, use an ohmmeter and measure to see. Is there continuity through that entire circuit? That's what you do to check for an open now, a short is very different, because in a short we isolate both ends, and now we can take an ohmmeter and we measure between them and now none of them should be connected. They should all be open line. So open line means no path.

There should be no continuity if they're all disconnected on both ends, so in other words, if i disconnect everything on this end, i shouldn't measure them connected together. On this end, using a no meter now, some of you may not be familiar with using an ohm meter. That's totally fine start there very basic. Take your meter, put it on ohm scale, and that's that's where you start you'll see.

You can measure through metals that are conductive, it's basically just showing how good of an electrical path you have the lower the number in ohms the better the path, and so when they're isolated like this, there should not be a path between any of these or to Ground and that's just as simple as taking one of the meter legs and scratching a good spot on a grounding terminal or maybe a piece of metal. That's in a condenser air handler furnace, getting a good grounding and then measuring to each one of these again. If they're isolated, all of these wires should remain isolated. I shouldn't measure anything on either side to ground.

If i'm looking for a short, that's what i would do, if i'm looking for an open, i tie them all together strip them back, tie them all together and measure between each one of them, and now i should have a path on all of them. If i don't have an open so again, if i'm checking for an open, i tie them all together on one end, if i'm checking for a short, i leave them all separated and measure between them and to ground, and that works whether or not you're dealing with High voltage low voltage, no matter the circumstance, a quick caveat is is that when you're using a typical, you know sort of typical grade multimeter that most of us use those multimeters don't use a lot of voltage in order to measure continuity or resistance to the circuit. Using the ohm scale, and so sometimes they'll give you a false reading and you won't find the problem and that's where a quality mega meter is going to be helpful, because now you can test in between each one of those. You wouldn't want to take a mega meter that you don't have an adjustable voltage scale that you can bring way down and use that on control wires.

That's where some of the the best mango meters out there have scales that go all the way down to 50 volts. That would be much more appropriate, for example, measuring on a control wire, and you never want to use a mega ohm meter. If those conductors are still connected to their loads and potentially to circuit boards, or things like that, you have to make sure that you're isolating when you're using a mego meter. But again, all that's doing that's different than your regular multimeter and the ohm scale is it's.

Just increasing that voltage and it's going to help you find problems a little bit more accurately, but again, the main thing i wanted to talk about here today is is the difference between a short circuit, which is an undesigned path of low resistance and an open circuit Which is no path at all: open circuit, no path at all short circuit, undesigned path of low resistance, and maybe you can even just say an undesigned path. In general, there are some shorts that actually won't result in an over current condition or a current. That's too high, in other words, you may have a short that doesn't trip the breaker or below the fuse, but it's still a problem. So really any time.

There's an undesigned path, meaning electrons, are allowed to move in a place that they're not supposed to, because terminals are touching or because there's a short inside of a compressor or whatever. The case may be just to talk briefly about this in terms of a compressor on a typical single phase. Compressor, you have your common, you have your start, you have your run and if we're measuring for an open, we measure from terminal to terminal and we see if we have continuity or if we have a resistance reading in between all of them generally on compressors. That's going to be a pretty low reading.

If you want to check for a short, then you take each terminal and you measure to ground it's very, very difficult. To look for a leg to leg short. Some people will say that while it was shorted leg to leg, that's that's actually pretty rare. I mean it can happen, but more often than not it's going to be shorter to ground, and even if you, even if you have a leg to leg short, it's going to be shorted to ground and the reason i say this is because that's one of the Most common misdiagnosis: i've talked about this a lot but technicians who go in and they measure with an ohm meter between the terminals.

They see a low resistance on the compressor and they say it's bad, but compressors have a low resistance just out of the box. If you look at, for example, the copeland mobile app you'll see that the resistance measurement from terminal to terminal is actually quite low, and it's designed to be when you're looking for a short circuit on a compressor or a motor, generally you're going to be measuring the Ground and that's where you're going to find that short circuit, not to say you can't have a leg to leg short, meaning windings within the motor that are shorted to each other. That can happen just trickier for you to find, and so i would want you to be much more experienced before you get to the point that you're comfortable doing that or you have some manufactured data that you can look at to ensure that you're not just seeing A low resistance thinking that it's bad when in fact it was supposed to have a fairly low resistance. So hopefully, that's helpful, open versus short.

Don't confuse the two and make sure that you're using the proper diagnostic procedure to find the problem that you are facing. Thanks for watching we'll catch you on the next one.