Resistors in alarm systems... Everything you need to know and more!

Alarm System Resistors - Basic usage to advanced


Below is a transcript of our video all about using resistors with alarm systems. If you would rather view the video than read, here is a link to the video:

Resistor usage in alarm systems

Hi, I'm Jason with alarmsystemstore.com. In today's video, I'm going to talk about using end of line resistors on your zones. Let's start very basic and talk about what a zone is, then I'll talk about what resistors are, and why you should use end of line resistors. The main focus of the video is going to be on single end of line resistors, as those are the most commonly used. But we'll also talk about advanced resistor uses, putting an end of line resistor in a can, doubling the line resistors, and I'll briefly touch on zone doubling, as well.


So what is a zone? I like to think of a zone as a circle or a loop. So at one point in the circle, you have the panel, and electricity will flow out from the panel and then back to the panel. You can think of a sensor as a switch, like a door and window contact, for instance. When it's closed, the electricity will still flow through the loop, through the sensor, and back to the panel. When it's open, then the electricity will only flow to that sensor and not make it back to the panel.


And you can have two different configurations, either a normally closed zone or a normally open zone. On normally closed zones, the alarm triggers when the flow of electricity is stopped. And this is the most commonly used. It's used for things like door and window contacts, motion sensors, glass break detectors, etc. We generally recommend using one sensor per zone, but you can use multiple sensors by wiring them in series. And whether you have one or ten, it will work the same way. When all the sensors are closed, then the loop is complete and the electricity will flow through the sensors and back to the panel. When any one of the sensors on a zone is opened, then the electricity will flow to that sensor, but not past it. And in this case, triggering an alarm.


A normally open zone is the complete opposite. So the alarm is actually triggered when the current completes the loop, not when it's stopped. This is very commonly used for smoke detectors, but it can also be used in other specialized instances. And it's pretty common to wire more than one smoke detector together into a zone. To do this, you'll actually wire in parallel instead of series. So when all of them are open, then the flow of electricity does not make it back to the panel. But if any one of those is closed, then the flow of electricity will flow to that sensor and then back to the panel. And thus causing an alarm.


So what are resistors? A resistor is just a device that impedes the flow of electricity without stopping it. There's different ratings of resistors, and even each panel will require a differently rated resistor. In this video, we're going to be using DSC's rating which is 5.6k, or 5,600 ohms. So what our resistor's going to do is actually supervise the wiring. So you would be able to tell, for instance, if you have a short in your wiring. This will most commonly protect you against installation errors. Maybe you accidentally shorted a wire at the panel, because you cut off too much insulation. Or maybe you're hanging a picture and you put a screw or a nail through the wire and shorted it out. But it will also potentially prevent someone from tampering with your wire and shorting it on purpose. This is especially true if you have exposed wires.


The resistors need to go at the end of the line because they will only supervise the wiring from the resistor to the panel. So if you put the resistor at the panel, it's, again, only going to supervise the wiring between the resistor and the panel, which is now wiring. That's why you need to put them at the end of the line and why they're called end of line resistors. Putting them at the panel is going to do nothing for you.


So let's look at a normally closed zone, just a simple one sensor zone with no resistor. So when it's closed, the panel's going to, again, send out electricity, it's going to go through that zone and back to the panel. And it'll see zero ohms of resistance. When it's opened then the electricity is going to stop at the sensor and not make it back to the panel. This is equivalent of seeing an infinite resistance or infinite ohms. If it's shorted, then the electricity will actually travel to the short, and then back to the panel, and the system will see zero ohms. This is a case whether the sensor is open or closed because the electricity isn't even traveling to the sensor. So without a resistor, when the sensor's closed, it will see zero ohms. And when it's shorted, it sees zero ohms. You can't tell the difference.


Now if we put a resistor in series at that sensor when it's closed, the electricity will flow through the loop again, but it will also travel through the resistor, and the panel will see that resistance of 5.6k and know that the sensor's closed. When it's open, again, it will show infinite ohms because the electricity is not making it back to the panel. Now if there's a short anywhere along the wiring, it'll travel to that short and then back to the panel. It won't travel to the resistor, and so it will show zero ohms of resistance. Now the panel can tell the difference between that short of zero ohms and a normally closed state, which is 5.6k ohms.


Now on a normally open zone, we'll actually put the resistor in parallel. So it's a little bit different. So if the sensor's in its normal state of open, then the electricity will actually travel through that resistor and back to the panel because it won't be able to travel through the sensor, but it can go through the resistor. So when the sensor's open, the panel will actually see 5.6k ohms. Now if the sensor closes, the electricity's going to take the path of least resistance. It will travel up through the wire and then through the sensor because there is less resistance going through the sensor than going through the resistor and back to the panel. And so it will show zero ohms when it's closed. Now on a normally open zone, if the wire is cut is the only time that you should see infinite ohms on the panel.


So let's go to the table now and look at a few of these examples. So we've got three different examples here. We have a normally closed with an end of line resistor. We have a normally closed with an end of line resistor that's not actually at the end of the line. It's going to be at the panel, and this is how you don't want to do it. And I also have a normally open zone with an end of line resistor. So I'm just using simple door contacts here. You've got the regular sensor with the magnet. So you can see when the magnet is attached the electric flow's gone through the resistor back. And you can see it's at 5.52, or about 5.6k. So when the sensor's open, you can see it maxes out. It says I can't read that much resistance. I'm not getting anything. So that's the infinite. So if it's closed, again, it goes back. So what I'm going to do is actually twist these wires together so it's gonna be a short. So now what you see is basically no resistance. It's showing 1.2, 1.3, and that's with it closed. If I open it up, still showing basically no resistance.


Now let's look at the circuit with an end of line resistor at the panel. So when it's closed, you can see 5.52 again, same as before with the last one looks fine. You open it up, it shows infinite. It's not getting anything back. But now let's do the same thing. And this short is actually really close to the panel. Showing 5.52, close it still shows the same. That's because the electricity is actually flowing to the short, back down through the resistor. So this looks like a normal zone even though it's not functioning. The panel can't tell the difference. So this is how you don't want to do it. It's not giving you any information. You might as well not use it.


Finally, we have the normally open zone. So this is in the normal state right now. The magnet's not next to it, it's opened. And as you can see, since this resistor's in parallel, it's flowing through that resistor because it can't get through the sensor back and we're getting 5.53. If I close it, now it's showing 1, it's basically no resistance. That's because the electricity's taking the path of least resistance. It's just gone straight through this closed switch and back. Now the other thing this can check for is if the line's broken. So we'll simulate that. You know it came loose from one of the terminals? It's showing infinite resistance.


If all you need is single end of line resistors, and most people, that'd be enough, you can stop watching the video now. But I am going to now go over some more advanced stuff, so if you're curious or you need more information, go ahead and keep watching. So the first thing I'm going to talk about is the normally closed single end of line resistor in the actual can. Now the resistor's not going to be attached to the panel but it will be at the panel. So as you can see from our wiring here, we're basically just extending one of the sides so that it runs to the sensor, back to the panel. We attach a resistor there, and then we run it back to the sensor. And then the other side runs straight from the sensor to the panel.


So to do this, for instance, you'd use a four conductor wire. And so you have your green, yellow, red and black wires. So at the panel, you're gonna connect green to a zone terminal and yellow to the other zone terminal. You'll then put a resistor between your red and black wires. Then at your sensor, you'd put the green wire in the sensor, and the red wire in the sensor, and then splice together your yellow and black wires. And so what this will effectively do is make the end of line resistor be in the can but still function as a end of line resistor. And so we'll go ahead and go to the table now and I'll show the example of it.


So here's our single end of line resistor circuit, but we have the end of line resistor actually at the panel. It's not attached to the panel, but it is at the panel. So you can see, here's our two terminals and we have green and yellow attached to those. And we have our black wire spliced together to the resistor, and then the resistor spliced to the red wire. And at the sensor, you can see we have the green wire, and the red wire attached to the sensor, and the black and yellow wires spliced together. So when it's closed, you can see that it's 5.51, that's what the panel's looking for. If it's open, we have infinite. Now, if we take this and twist it together to short it out, you can see even though it's open, we're at 0.9 resistance. Close it, no change. So that means there's a short in the line. So even though our resistor's gonna be in the can, it is still functioning as an end of line resistor because the resistance is just running up this green wire, being shorted out with the yellow wire, and running back down. It's not running through this resistor. So the panel would still show a tamper, even though our resistor's at the panel.


So the next resistor concept I'm going to go over is using double end of line resistor. So this is going to be kinda a step above single end of line resistor as far as the things that the panel can see based on the amount of resistance. So just like with the single end of line resistor, you'll have a resistor in series with the sensor, but then you'll also have a resistor in parallel at the sensor. So this will give the panel basically four different resistances it can see. So zero ohm resistance would still be a short. It's not running through either resistor, it's just a short. It's running up to the short then back to the panel. No resistance.


If it sees 5.6k or one of the resistors, then it knows that it's closed, because it's running up through the sensor taking the path of least resistance, through the resistor in series, and then back to the panel which should be 5.6k. Now if it's open, it will run up to the sensor, it can't get through the sensor. So it'll go around the resistor, so 5.6k there. But it'll also run through the resistor in series. So it's going to see another 5.6k for a total of 11.2k. And finally, if the wire is cut, so there's no way for any current to get back to the panel, it's gonna see infinite resistance and so it'll know that the wire is cut. And we'll go ahead and go to the table and show that as well.


So now this is our double end of line resistor. So you can see we have a two conductor, spliced together with a resistor in series. And then there's a second resistor right here that's in parallel. So when this sensor's closed, you can see 5.55 resistance. When it's open, it goes up to 11, and we're looking for about 11.2. So that's within the tolerance of the panel. But now we can short it and you can see one resistance open and closed stays about that. If we un-short it, close it, back to the 5.5. Now we can also check if there's a break or it comes loose from one of the terminals. You can see it goes up to infinite resistance. So you can see how that shows you four different states of the wire here.


Finally, the last iteration of one of the end of line resistors is going to be zone doubling. Now this is used like on panels such as the Vista 20P. What it does is it'll actually combine two zones into one hard-wired zone, allowing you to basically double up on one zone. So what you do is wire two sensors in parallel. And with each sensor, you'll have actually two different values of resistor. So one value of resistor wired in series with one of the sensors, and the other value of resistor wired in series with the other sensor. So based on which resistances it sees, whether it's one or the other or both, the panel will know which zone is open or closed. We generally don't really recommend using zone doubling. We find that it's a little bit easier and better to use just an expansion board instead. And this doesn't really increase the amount of zones you can use. You're not really getting anything extra out of it either. So that's all the iterations of end of line resistors for your zones. I'm Jason, once again, with Alarm System Store. You can visit us on the website. And you can also give us a call at 888-811-0727. Thanks.