How to Test for Resistance? What is Continuity?

how do we test resistance and why would we [Music] all right so something that's a little bit less common out in the field is the use of the resistance setting on a multimeter or a tester right here I've got a desktop DMM digital multimeter and then I've got a field tester one thing to note about these two testers is that this tester is uh thousandths of an OHM so when it displays values whereas this one might read 0.2 ohms this one will read 200 ohms so you have to understand the differences between different multimeters and when you get a reading what it's actually calculating so I put a couple of different things here that we can test so we can talk about maybe why you would use resistance why it's useful and not even necessarily just resistance but continuity as well so when you look at a multimeter you have a symbol that is the ohm symbol or the omega symbol in the Greek alphabet that is talking about resistance values this has different ranges so it'll sense anything from you know thousandths of an OHM to a single ohm home to 10 ohms 100 ohms it has a huge range of what it'll detect so I like to use dmms anytime I'm doing resistance because the amount of resistance that you're going to offer in a filament of a light bulb is going to be different than a fuse which is also going to be different than an entire roll of wire at the end of the video stick around because I'm going to show you how you can actually use a Multimeter to tell how much wire is on a reel without having to guess and like roll the whole thing out so uh first thing with the DMM you got to make sure that you're into the right settings on here it actually shows ohm so the black one is always going to stay where it's at you notice on a DMM that you've got three Reds and you have a black so black always goes where it goes if you're testing a lot of amperage that's a 10 amp fuse that connects between here this is 500 milliamps and then over here it shows the ohm symbol so it tells you what to do when you're using all these different crazy settings on here so we're going to go to the resistance setting now the first thing that we're going to talk about is just a fuse this thing has continuity to it so from here through one lead to another lead and all the way back to the meter it can detect if there's a loop this is super helpful for us out in the field a lot of times if you don't know what wire is what you got a few wires sticking out at you you can take a black and a white that are in the same one piece of Romex strip them out and touch them together and put a wire nut because on the other end the black and the white should now be because there's a wire nutted together there should be a full loop from beginning to end so you can use continuity and it should tone at you like this to tell you that there's a loop so the continuity aspect of testing like this is really helpful a lot of times out in the field we will have a silly thing as a fuse that blows so you might have like a three-phase environment you've got a fused disconnect two of your fuses are fine your third one's not you have customers complaining that like sometimes there's lights some of the lights and some of the receptacles in the building are working but other things aren't could just be that you lost a phase at the utility but a good thing to check if you you get called out there is the fuses at the service disconnect so the way that we test a fuse is one of these leads on each end so we should get a tone that lets us know hey we got a good fuse if there's no tone that means uh-oh fuse is broken a lot of times they're clear fuses like this one so you can actually look in there to see and make sure that it's not broken but the continuity aspect of this is huge we use continuity all the time another way that you can use the continuity is to check to see if a light bulb is good or bad now this isn't going to work on compact fluorescence or LEDs anything that's like gas filled hid figure lamps and stuff like that where you have a gas ignition on the inside a gas tube anything that you have a filament though that goes from one side to the other piece of metal should ring continuity so here's another thing you can take on the shell of a light bulb because that's your neutral side and then you can take it on the bottom boom we got a good filament in there if there's no tone you know this thing's bad sometimes you can tell by like shaking it a little bit sometimes you can't sometimes it just sound trashy and old but they actually still ring through continuity-wise so that's another thing to do um between the two I want to show you some values so this will tone and it will show you actual values you've probably seen this thing um moving back and forth and it's telling us value so this filament right here that's telling me that it is 0.1 ohms right so that's the amount of resistance that it's offering to the amount of current that's flowing based off of the pressure the EMF that we're pushing through the difference of potential over a certain resistance is going to allow a certain amount of current flow so if you're ever sitting doing Ohm's law calculations your resistance is variable you can change resistance the resistance in this tiny little filament is going to be way different than say like the resistance of this element so let's see what the resistance value of this light bulb shows look at that 214.8 ohms notice that there's no ringing there's no continuity so to the to this multimeter this doesn't look like a closed circuit there's a lot of resistance that's a big number so there's so much resistance that it's kind of acting like an insulator somewhat compared to that that filament this thing there's barely any resistance at all right so this thing has a whole tiny little element that's wrapped around um so to the to this multimeter it's showing a lot of resistance so that was in the 200 range what about this thing what is this show 's continuity so my guess is it's going to be less because this thing thinks that it's just a piece of wire a little resistance yeah we've got 16 ohms of resistance on it so you can see the value right like either you can use it for continuity when you're testing things and you're trying to see if something's broken or not or you can actually use the resistance values now you're not going to need to know the resistant values of a light bulb when you're out in the field but you might have a heating element that's inside of an air handler or a furnace and you don't know what size the element is there's no sticker it's not stamped on there and you're like damn it I'm just trying to figure out like what size element is this well if you get a resistance value then you can figure out because you know the applied voltage now you know the resistance from what you're testing so now you can do a calculation using Ohm's law to figure out the amperage to know what wire size to run to the element so that's a reason that we might do this out in the field in that example say that we have a 240 volt circuit that we know that we're going to be supplying some heating element in a furnace so that furnace we don't know what the actual KW rating is there's no stickers that you know we can't when we look at the element there's nothing on there that marks it so we have no idea how much current this thing's going to draw so if we can get a resistance Value Cross that element with our multimeter say we we pull our multimeter out we test and we get 5.77 ohms well now we have two different values to figure out our third value so we would use Ohm's law for that we would plug in 5.77 for the resistance we would plug in 240 for the voltage we're trying to solve for I so I equals e over r I is your current 240 volts is your voltage and 5.77 is your resistance 41.5 so we could say that the current is 41.8 we'll say six amps so we know 41.6 amps okay so I don't even know what KW rating this thing is but I know with whatever the resistance of these elements are that they're going to draw 41.6 amps because of the resistance on them you could even go one step further and we could figure out what KW rating that is so instead of using Ohm's law we're using joules law for power so if we're trying to find power we multiply current times voltage so it's 240 times 41.6 9984 that is a 10 KW heating element that's going to draw 41.6 amps another thing that you can try to figure out is a lot of um resistance that you get on light bulbs if you know that you've got like a fixture and you can't get to the bulb and it's like way up and you don't have a bucket truck with you you can figure out what the wattage of a bulb is so any kind any like little bit of information that you can pull off of things you can plug into Ohm's law or into the power wheel and move those things around to get your unknown so the things that you don't know so last thing that I use this for and I just always thought this was cool some old school electrician showed me this a long time ago every bit of wire in the back of the national electrical code chapter 9 table 8 shows a certain amount of resistance that's based off of the size of the conductor so down the left you've got all these different conductor sizes every single conductor is going to have a certain amount of resistance to it when you pass current through it it's going to be different if it's aluminum it's going to be different if it's copper but it's in thousands of feet so if I'm looking at a uncoated copper conductor or a coated copper conductor I have different values to go off of so what I'm going to show you is that if you go to uncoated under copper and you go to ohms per kft which is thousands of feet so if you look at the fourth column from the left it says quantity it shows one and seven well one means one conductor it's a solid conductor seven means stranded because there's seven stranded conductors in that number 12. go down to number 12 so you can see those two different values they're pretty close when you go to uncoated ohms per thousand feet it shows that a number 12 stranded is 1.98 ohms per thousand feet okay so we know what a thousand feet should show up on a multimeter if we're reading it so what do you think is going to happen when we have a 500 foot roll brand new of number 12 stranded well if we know a thousand feet is 2 ohms we should roughly get one ohm if it's 500 feet so let's see what we got [Music] 0.9 so that goes to show you if you've ever got a reel of this and it there's like half as much on it and you're at the shop and you're like man I've got like a I've got like a 75 foot run and I can't tell if that's 100 feet or not dude pull out your multimeter go know that it's 2 ohms per thousand feet and then just do the math walk it backwards to figure out how long the wire is so that's a cool trick so that is using resistance testing for resistance I would be a little careful using different testers especially using a tester not a digital multimeter usually digital multimeters you get a little bit higher range some of them are Auto ranging so it'll give you it'll move the decimal around for you whereas this thing's not this thing's really just meant to be a voltage and amperage tester and give you some continuity so uh having it in thousands of ohms is a little bit less helpful but it's specifically meant for voltages for resistances and for amperages that you're going to run into as an electrician most of the time in like 120 uh 240 480 volt environments but if you want something a little bit more Sensitivity I would go with a DMM like this that's got a lot of different range so they thank you guys so much for watching uh leave some comments below if you got some comments I'll see you guys in the next one

Channel: Electrician U

Views: 207,956

Keywords: electrician, electrical, electricity, dustin stelzer, electrician vlog, construction, commercial, residential, electrical vlog, electrical courses, electrician courses, electrical class, electrician class, electrician school, how to test for resistance, multimeter resistance, testing continuity in a wire, electrician u, how to test a long wire for continuity, amperage continuity, ampere meter, amps volts resistance, power issues, national electrical, skilled trades, terms of trade

Id: -yYjWg4UXow

Length: 11min 32sec (692 seconds)

Published: Wed Feb 22 2023