In this episode, we discuss the key electrical concepts that a BAS professional needs to understand.
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Phil Zito 0:00
This is the smart buildings Academy podcast with Phil Zito episode 317. Hey folks, Phil Zito here and welcome to episode 317 of the smart buildings Academy podcast. And in this episode, we are going to be shifting gears from our sales conversation that we've been having the past several weeks. And we are now going to be focusing in on some more technical concepts. So today's episode is going to be making sense of electrical concepts without becoming an electrician. So we're going to be looking at Ohms law, we're going to be talking about the relationship between current resistance and voltage. We're going to talk about why you see the volt amperes drop on transformers, as you turn on more devices, and turn on more outputs. So we're gonna cover a lot of concepts related to electricity. Alright, as always, everything can be found at podcast at smart buildings academy.com forward slash 317. If you're watching this on the live stream, welcome, make sure to add your comments as we go through this episode, make sure to like and subscribe as well helps grow the channel. And if you're listening to the podcast, then definitely wherever you're listening to this, add your questions and comments there as well. And we will go and discuss those. Let's dive in. So what do you need to know in regards to electricity and this is one of the things that, you know, back when I was first starting off in the field, I was trying to figure my kind of place in the field out, I went and applied for an electrical license. And I started the process of pursuing that I gave up on that because I realized it wasn't necessary. It's kind of where a lot of folks end up, you come into this industry, from a variety of different backgrounds. Some folks come from a mechanical background, other folks come from an electrical, some come from an IT, some come from a military background like myself, and really figuring out what you need to know that is one of the biggest challenges. Because if you talk to someone with an electrical background, they're gonna say, Hey, you really need to understand all of this electrical stuff because they lean on that. But you may not need to know all that stuff. And then if you go under someone with a mechanical background, they're gonna tell you, you know, hey, pursue an apprenticeship really become a mechanic understand the systems first. And in reality, I've never changed a compressor in almost 20 years now. And I'll tell you that a lot of what you would learn that path is unnecessary. So the purpose of this episode is to really explore some key concepts and understand how all this ties together, I will do my best to take a visual concept and turn it into audio for those of you who are listening to the podcast do realize that at podcast, smart buildings Academy comm forward slash 317, there will be a video accompanying this as well, already. So continuing on this electrical concept, you've got ohms All right, volts, current resistance, these come together to form what is known as Ohms law. We'll
talk about the relationship here in regards to how this all works. But what we have to understand in a traditional building automation system, we have a transformer and this transformer quite simply transforms power. Typically it's what's called a step down transformer. And it's going to typically step down voltage typically 120 Volts AC and it's going to step that down to 24 Volts AC and in the process this transformer is going to have what we know as VAs or volt amperes. So one of the things I first want to talk about here with Ohms law and just electrical concepts in general is you have volts that's one measurement, right volts electrons flowing across the wire, you have aI which is resistant or sorry is current which is known in the term of amps. And then you have r which is known in the term of ohms which is resistance. So volt amperes is quite simply the ability to transport nutrients For this power from the transformer to the end device. Now what does that look like? So we have a transformer, and our transformer has on the secondary side. So you have a primary side, which is the incoming power to the transformer, especially with a step down transformer. And then you have the secondary side, which is where we're primarily concerned as controls folks. And the secondary side is where we have our 24 volts AC. And typically, we'll have transformers that are rated like for 40 Va, or 100, va excetera, right. And what happens is, as this transformer goes and feeds a controller, oops, a trauma pen, this thing is so small, I needed a bigger pen. So as this transformer feeds to this controller, this building automation controller on the transformer feeds from the secondary side to the controller, then this controller is going to have potentially internally sourced voltage. And this voltage is potentially used to drive devices. So you'll see where controllers have internally sourced voltage to drive what are known as coils more on that later. And you'll also see where transformers go directly to the control device like maybe an actuator and they actually enable the motor of the actuator to be driven. Now, what happens is that whenever you are going and using a transformer, sure using a transformer, and this transformer is going to a resistive load, a motor impedes the transfer of electrons. So what happens is electrons volts are the power and this transformers providing that power. And what happens is, is when that power hits this device,
it starts to impede the flow of the electrons. And since volt amperes VA is current times volts, obviously the electrons decrease, and our VA is going to decrease the capacity of the transformer to provide that power to drive devices is going to decrease as we activate more devices off the secondary. So you've got this one concept right here, where this load this actuated load goes and causes the transformer to have less VA to have less power to be able to then go and drive devices. Now what's happening is you will see that on a transformer or on a controller like if we were to bring up a controller catalog sheet, what would happen is the controller catalog sheet would say an unloaded controller maybe requires 14 va but requires 40 va when it's fully loaded. That's because the controller is sourcing voltage to drive outputs. And as it drives outputs, those outputs have certain amp ratings and voltage ratings, which then decrease the VA capacity of the transformer. So to put that in another way, is if you've ever used a garden hose, and you've interrupted that are not a garden hose, a drip hose to do a garden, and you've run water to that drip hose. And as you go from drip nozzle to drip nozzle to drip nozzle, the pressure gradually reduces to the point where you go from a potentially strong drip to a very weak drip further down that drip hose line. Well that's the same concept of a transformer and decrease in VA. As you put more resistive loads on to that circuit, then we are going to see a decrease in power ability to the point where it can get so low, that devices cannot fully actuate or in a worst case scenario. Controllers actually start to go online and offline. That's why sizing your transformers. For a accurate VA loading is critically important. So so far, right? We've covered these concepts of a transformer. We've talked about VA, we've talked about ohms law and somewhat the rest lationship between these things. So if I were to blow out um, slaw even more onto the screen, you would see that how it works is kind of like this. And what I'm drawing is a V at the top with division with dividers for both current and resistance. So current times resistance, right, is going to equal voltage. But if I want to get voltage, then or sorry, yeah, yeah, it's going to equal voltage, if I want to get current, then what I am going to do is I'm actually going to divide voltage by resistance, and that's gonna equal current. And so that's kind of how all of this comes together, is this equation works, you know, as you have one variable to solve, you can or you have one variable, you can go and solve the other variables. Or sorry, if you have two variables, you can go solve the one variable. Gotta love math, I hate math.
People have followed this podcast for any amount of time, know that I hate math. Alright, so continuing along this concept of voltage, current and resistance. On a circuit, we have what is called a circuit. And we typically use circuits extensively in building automation. And what we use circuits to do typically is we will go energize coils. And we will use these coils to change the states of contacts. This is a very, very common approach to a lot of building automation problems, you want to turn on a fan, we go energize a relay coil, and we allow voltage to pass through the contacts. And those contacts will energize a starter, energize a motor, etc. So what I'm drawing on the screen right here is a circuit with a circle on it, which is a coil. And that coil gets energized. And when that coil gets energized, it changes the state of the contacts, which are these metal contacts, basically, and they open and close based on the energization of this coil. And as those contacts change state, they either create a complete circuit to allow voltage to pass through, or they don't. So what we would have is maybe something like what I'm drawing on the screen is a normally open set of contacts. And as a coil gets energized, that normally set of contacts or normally open set of contacts closes. And then we have hot and ground as a circuit. And somewhere in between. Excuse me this, we will have a device maybe like a starter, and that starter will get energized. And as that starter gets energized, that then allows a fan to turn on. Now to pull in that coil requires a certain amount of amperage to go and energize starters directly requires even more amperage. And that's where some of this VA loading concepts comes from. So this is a key concept that you need to understand a building automation. So in building automation, we need to understand circuits, we need to understand coils, we need to understand closed and open contacts, transformers, secondaries primaries, and the effect of resistive loads on the secondary from a VA power perspective. So a lot of concepts swirling around. And I'll point you to some resources we have at podcasts at smart business academy.com forward slash 217. Or sorry, 317. Oh my gosh. So we've talked about ohms law, we've talked about VA, we've talked about transformers, we've talked about circuits. Now let's talk a little bit about input and output types and how those exist from an electrical perspective. So on the input side, we will typically have resistive Did you digital volt DC, milliamp and pulse which I'm not really going to talk about too much as our input types. And each one of these input types requires different wiring approaches in order for them to operate. So resistive element quite simply, you just complete a circuit with the resistive element in the middle of it. And that resistive element whether it's like a 1k nickel or a 10k type two or type three thermistor those are going to go and since temperature typically digital is typically a ON OFF state. So this would be something like a contact closure, where you are either sensing resistance or you're sending a five volt DC signal through this contact closure. And as you sense that signal the controller knows that the state has changed from either on off openshot etc. These are used for end switches like on actuators and switches on or sorry, on dampers. These are used for like fan status with flow switches. These are also used as auxilary inputs from safeties like low temp safeties, etc. volts DC. This
is another one, that's pretty straightforward. It is polarity sensitive, which we haven't talked about yet, but we will talk about in a second, but it's very similar. In that you route one side of the inputs to the input side and the other side of the input to the common side. And you may have to power this sensor externally, with an external transformer. Sometimes the controllers actually have their own power and milliamp is very similar. In that you go and pretty much wire it up the same. There is a little bit of nuance on some controllers that involves resistors. That involves doing things a little differently. But for the most part is wired up the same as well as sourced how you measure volts DC and milliamp is a little different. Because volt DC, you can simply measure across the contacts and you can be like, Okay, this is five volts, whereas with milliamp you either need an amp clamp to detect that amperage that heat that current, or you need to measure that current, what is called in series. So volts DC you can measure in parallel, you can put your leads across the wires, your multimeter leads, and you can call it a day and measure it milliamps you either have to have an amp clamp to go and since the current or you have to measure what is called in series, so you have to interrupt the wire and actually put your leads in between one side of the wire to the other side of the wire to detect that resistance or sorry, that current. On the output side.
Unknown Speaker 17:04
We have three primary outputs, we have voltage,
Phil Zito 17:10
which is either internally sourced or externally sourced, this is typically 24 volts AC, although it can be 120, you don't typically route that through a controller though. And that is going to enable those coils that I mentioned earlier, it's going to energize those coils to go and affect those contact closures. You have volts DC output this is commonly used for a proportional valve actuator, or for like a VFD control signal. Typically zero to 10 volts DC polarity sensitive, which we'll talk about in just a second used to drive VFDs used to basically give a proportional a variable control signal to drive a device. And then you have milliamps. The big difference between volts DC and milliamps is that with volts DC, those tend to be shorter runs that are not prone to electrical interference. Ma milliamps tend to work well with longer runs that are potentially subject to interference. That's because current right if we go back to ohms law, current is created by voltage divided by resistance, where as voltage is created by current times resistance. So as we have that resistive effect, we are going to see more and more that we have some issues with our faults. And we're also gonna have signal degradation from just noise in general, over a longer distance. All right, I always second guess myself, whenever I'm doing ohms lol equations like that it wasn't volts equals I times R was a divide, I was mixed that up no matter how many times I've taught it. Man, it's just kind of one of those things that I'm always self conscious about. So I mentioned polarity. And when we're using volts AC, we're using what's called alternating current. And if you think about a battery, a battery has a positive and a negative side on it, right? It's true negative as a vertical line, there's a horizontal line for negative. So what happens is the electrical, in the case of AC it alternates between positive and negative. And so it's called alternating current. So if you were to plug in an AC circuit, it's what's known as polarity insensitive, meaning if you hook up a hook up the positive side to the negative side or the negative side to the positive side, it's not really going to matter. Whereas if we use direct current, we are doing a direct current, which is going to look more like a block on a multimeter Oh my gosh oscilloscope and what will happen is our positive will be positive and our negative will be negative. And if we crossed those wires, we are going to cause the signal to basically be inaccurate and improperly controlled and cause all sorts of issues. So we need to be cognizant of the polarity sensitivity of volt DC wiring. Okay, so at this point, we've covered Ohms law, we've covered input and output types, we've covered circuits, we've covered polarity sensitivity, and we've covered transformers and secondaries and how loading on the secondary reduces the power capabilities of that secondary to transfer power to whatever devices we're doing. So continuing right along. The last thing that I will leave you with here, in regards to this electrical concepts is going to be just a little tidbit in regards to controllers and amperage,
excuse me. So on inputs and outputs, controllers have amperage ratings. And remember amperage is heat amperage, is current. And if we have too much amperage, we can damage our internal components to our controllers. So we need to be cognizant of the amperage ratings of our inputs and outputs. When we attach devices to them on the controllers so that we don't damage the controller. This becomes specifically important when we are using an externally sourced power and routing that through our controller output. So if we have a relay output inside our controller, and that relay opens and shuts inside our controller, then we need to be cognizant of the amperage rating for that output so that we don't go and put too much amperage through that output that can cause the controller to be damaged, sometimes permanently. And that can just be a very bad thing. So there you have it, some electrical concepts. This is by no means a sweeping electrical course. But this should give you some understanding of baseline terminologies. If you do want to dive deeper into these electrical concepts, we have a much more formatted and structured course on wiring and installation of control systems inputs and outputs. You can check that out at podcasts at smart buildings academy.com Ford slash 317. We'll have a link to that. And as always, if you have any questions, please do not hesitate to ask. I'd love to answer your questions. And thank you so much for being here. I will see you in the next episode. Take care
