How to Use Multimeter Readings for Electrical Troubleshooting | TPC Training

hello everyone and welcome to today's public webinar for tpc training entitled understanding multimeter readings for electrical troubleshooting we're going to spend about 45 minutes together today really understanding the different readings we can get and what they mean when it comes to testing uh electrical circuits with a multimeter my name is ryan smith i'm an instructor with tpc training and also product manager with tpc training i'm going to be walking you through some of these multimeter readings here today so in advance of this session i want to make sure to let everyone know that this session is being recorded so if any of you or your colleagues missed this session feel free to watch it back on our website um and we'll send you an email to with that link within two to three business days of this webinar and you'll be receiving a pdf of these slides as well a second thing i want to let you all know is that we're going to be taking questions and answers during this session so this is a live event right now and what that means is that i'm just not a pre-recorded voice you can actually interact with me so i really hope that you do go to the q a tab on on your control panel here for this session and type away and finally we're going to be getting into some detail on my table top here to take a look at some a meter and some readings of different devices so in doing so i want to make sure that you make me as large as possible when i stop sharing this screen here and make sure that the video feed of me is full screen then you should be good to go all right without further ado what are we going to talk about today so electrical troubleshooting first things first this meter here is going to be the one we're going to use here to understand multimeter readings and this really is a multimeter for a reason right it can measure multiple different things the three we care most about for this session and for almost any electrical circuit ever is current voltage and resistance so our first talking point today is to make sure we understand what current voltage and resistance is in a really quick kind of run-through way now this isn't a basis of electricity webinar however um you've got to know what those three are pretty in-depth to understand what you're getting on your multimeter then we're going to kind of break down the testing of each one we're going to understand ohm readings we're going to start with ohms and then we're going to go to understanding and measuring voltage in electrical troubleshooting in different ways and that one will be in a simulated voltage environment and then we're going to go to measuring amp readings as well so let's start with current right so what is current so current really is the easiest thing about electricity to understand right and that is that flow of electrons flowing in a circuit you might say well i can't see electrons flowing and you're right you can't see them in their microscopic format flowing but you can see electrons flowing all around you every day if you look in the room you are right now and you look at the lights shining on your head if you see a light shining that means that there's electrons flowing through that light producing that light for you right if you hear the hum of your air conditioner the hum of your heater that noise that you're hearing is indicating current flowing so the first step of any good electrical troubleshooting process is to listen and look right use your eyes and your ears to really see what some of the issues are that you're seeing right are lights flashing that means current is flowing to that light is a motor running is the three-phase motor humming that means current has made its way to that motor however the other two here voltage and resistance are not as easy to see into here right so that's really where we need this meter right because this meter can tell us a story that we can't see and that we can't hear with our own human senses and that's really where these become extremely valuable in fact the two most important tools i always like to say that for any electrical troubleshooter the two most important tools you can have is not a hammer or a screwdriver right tool number one is a multimeter a really well rated multimeter and the second tool you can have is you might not think it's a tool but it is and that is schematics so if you have a meter and then you have an up-to-date high-quality schematic you can do any sort of electrical troubleshooting job that you need okay so we're really going to focus on just the multimeter readings today again there's a lot of details to get into on here but we'll just give you a quick run through on this webinar let's talk about voltage voltage is really that difference in potential right so it has to do with not the electrons flowing but how energized those electrons are when they're flowing are they at really high potential or are they at low potential and then what is the difference between one spot and another so the biggest trap we get into is measuring with a meter just one spot and saying okay what's the voltage right there what's the voltage right there that's not a good way to go about understanding voltage it's really what's the difference in voltage between here and here so we're going to talk about that and measuring those readings and then finally resistance so resistance is the opposition to that current flowing that current right and it's measured in ohms which is an upside down horseshoe symbol and we're going to talk about that and it's really going to be up to us to understand what zero and ohms means versus an ol reading on an ohmmeter what that means so we're going to talk about that as well okay so let's really start by talking about ohm readings and in doing so i'm going to stop my share of my screen so i should be popping up larger for you now go ahead and make sure i'm as large as possible on your computer or monitor screen and i'm going to change my camera angle now to my tabletop camera so here's my table top and you can see the meter here on my tabletop so what we're going to talk about now is ohms first so we're going to start with ohms because ohms is the best to be measured when the power is off in fact even better yet you should only measure ohms when you are completely disconnected from a circuit entirely better yet you're testing ohms on a device that has been completely removed from a circuit on a tabletop like this one that's the best way to measure ohms on something whether it be a fuse or a control device like a button or switch or a relay or any other type of device that even including a three-phase motor get it out of the circuit and get it on a workbench or a table that's the best way to test ohms so you can see here this is a multimeter that we're using it's got ncv which is a non-contact voltage mode it can measure amps in ac so the squiggly line is ac and the straight line is dc we got voltage with the squiggly line that's ac voltage we got dc with the straight line voltage and then we have a bunch of different modes for the resistance so you can see the ohms the upside down horseshoe symbol here and this can also measure measure diodes capacitors and it can give us an indication then finally we can measure frequency in hertz and if we have a thermocouple attached to the red and black ports here we can measure temperature so what we're going to do now is turn this thing over to ohms right so this is time to measure temperature and the first thing i'm going to set it to is it gives us in audio so i set it to the little sound icon so it'll give us an audio whenever there's resistance but the first thing we're seeing here is o l right who can tell me what o l is who can bust the myth right what o l means well it depends there is an industry agreed upon term for ol and that is open line right open line that's the really the best way to understand what ol means open line some people get trapped into understanding um ol as being overload right or over limits that's kind of a misconception here it's definitely o l as an open line so that means something open and now what does open mean that's going to be a huge huge thing to understand when it comes to understanding what ohm readings give us open so it's telling us that between this red and this black lead is open and that really to us means that there's air or really very high resistance between the red lead and the black lead giving us the reading of ol so that really tells us that if we see ol it doesn't mean that there's no resistance that's something we get trapped into thinking that ol means no resistance ol actually means so much resistance between red and black that the little power supply in this meter can't get an electron from the red lead to the black leader vice versa if there's so much resistance that we've surpassed 99999 on this meter so it's just going to tell us ol that's really what that means okay so ol means very high amounts of resistance okay next if i touch these leads together now it's going to be very easy to make it from one to the other in fact there's nothing between us so it's going to give me a low ohm reading and it's beeping you should be able to hear that beep through my headphone if not it's beeping at me and we got pretty much close to zero ohms as close to zero as we can get right we're touching these two together so when we are not touching from red to black we are what we call not continuous or not having continuity that's the term we tend to use that there is no connection between where we put the red lead and where we put the black lead this can be measured on a device basis or inside of a circuit so i'm going to measure some devices here on the table like this red lamp here where we can measure its uh whether it's functioning properly or not i'm going to take a look at a push button on a control device side we're going to take a look at a relay we're going to understand how to do ohm readings on this relay and then finally i'll do a quick ohm reading on this motor starter okay so let's start with this light so what we're going to do is we are going to test this light so this light this light is something that should be doing work for us right it should be shining a light on us so anything that should be doing some work for us should have some resistance in ohms it shouldn't be zero it should be some sort of amount of resistance and so what i'm going to do here is test from the left to the right-hand side of this light and see what we get right and this has given me about we see that 27.5 ohms so that's really an amount of resistance here that this thing is actually good and it's doing some work it's able to do some work for us now if we took this light out let's say it wasn't shining out in the panel that it was in and we put it in and we went across it and we got ol right that means that the filament inside of this has burnt out or maybe the bulb is missing from this thing right so basically this thing is not working the way it should and now we pinpointed it to this light bulb instead of let's say a wire in the panel or a relay in the panel it was really this light giving us the issue okay let's talk about something that should either have no pretty much no resistance or pretty much all the resistance and these are what we call control devices so this light is what we call a load it's going to do some work for us it's called a load right whereas this button is what we call a control device and this is what we want to know how to test too with control devices like buttons and switches and relays too which we have to get used to the term of of um open or closed so we really have to understand what that is and it takes some practice and i highly recommend you continue practicing the terms normally open and normally closed right and so these are what we mean by that is it's allowing current through or not allowing current through so in other words has all the resistance or ol going through this thing or it has no resistance going through this thing it's just a pass-through and that's going to give us close to zero ohms right if it's working properly so what state is this selector switch in right now is this selector switch not allowing current through or is it allowing current through can you tell well i can't tell can you and that's really where this meter comes into play so let's test the selector switch to see whether we're allowing current through or whether we're not so let's say the lights that this is powering it's not coming on right we need to know whether the switch is in the right position so we turn it around like this and you can see the contacts in the back of this thing and we go from left to right again and we get ol right so what does that mean it's open so that means this is not allowing current through to wherever it's hooked up to right now so let's go ahead and switch it to its other position there it goes and now i'm going now flip it over and test it again and we're pretty darn close to zero ohms there we go so that means this is the closed position of the switch and if maybe we mislabeled this thing maybe we didn't label it in our magic marker in the field like we should have or whatever labeling we chose with this guy so this is a good way to know now what if both ways it measured oh well or both ways it measured zero now we know something's wrong with the switch right so that's one a good way to measure a control device whether at zero ohms or whether it has all the ohms or ol okay let's talk about relays next so this is a control relay has the the top part of the relay that's basically where all the where all the brains of this relay is and then it has the base where you can actually connect the wires this relay has two main parts it has a coil and a contact and what's interesting is that a relay combines a load like this light with the control device like this switch and it has both inside of inside of this small package so it has a load inside in the form of a coil that can create a magnetic field and push and pull contacts and then it has those contacts so i'm going to pull it out of the base i just pulled it out of its base so we just see these pins on the bottom that correspond to the numbers on the base okay so the two the two parts of this i'm going to move it closer so you can see it there we go so the two pins of this that correspond to the coil that that's the load part of this again i need to be careful that i don't lose my microphone it's a1 and a2 which are just off the center and you can see that when i put the leads on a1 and a2 we have about 70.7 ohms so what that means is that this coil that's going to push and pull these contacts in the field is working properly it's not burnt out at all right now i know you can't see these these are really small numbers but if we look on the side of this we can see what all the little what all the pins on this connect to right now so basically this connects from 9 to this one says terminal 9 to terminal 11. are normally open and then terminal 8 to terminal 11 are normally closed okay so here's terminal 11 right here okay and then here's terminal 9. just two away from it and we can see it's ol so that is open and that is correct then we go 1 next to it to 8 to 11 and that's normally normally closed and we can see it is closed right now now what if we wanted to make sure these can properly switch from open to closed or closed to open when we energize the relay i can't put a wire to this thing without shocking myself or having a circuit here but what we can do is simulate this thing by pushing up this little thing on this relay or there's a way to basically simulate the energized state on different relays they come in different shapes and sizes but this is the way to do it on this relay and we come back and we test 8 or 9 to 11 and 9 to 11 used to be ol now it is now it's giving us close to zero so that switched closed and then this one used to be zero and now it's oh well so these did their switch properly whenever this was energized so we really verified that this relay is doing well now if we ever measured from a1 to a2 and we got ol right that could mean that we burnt out the coil on this thing and we need to we need to go okay all right so i just want to make sure you guys can still hear me let me know if you can still hear me again if uh this headset might be going out on me and i'll have to have to get a new one for for you for the rest of the session okay cool all right thanks guys um yeah a good good size audience here so i appreciate it guys now the next thing i want to test for you is this motor starter here and this motor starter is an iec style motor starter and and what does it do well it starts a motor right but really what this thing can do um it's this thing has a bunch of auxiliary uses so what we see is that the three phases of a motor come in here and then they come out the bottom to start that motor and so what that means is that the top to the bottom are going to connect to the motor and start that motor only when this contact is pushed in here okay but what makes that pull in right i can press the button to pull that in or i can make it happen automatically by sending a magnetic field uh electrical signal to this uh coil here to produce a magnetic field which pulls this in automatically so one thing we can do with this motor starter is to make sure that l1 to t1 down here gives us zero zero and zero and then we can press this in here right and then measure zero or i'm sorry o l o l and o l to start with right o l o l o l and then we press this and then we get zero zero and zero so that's really a good way to make sure that the contactor portion which is the portion that connects the the three phases of a motor down while starting the motor the next thing we can do is test this overload contact down here so this thing is going to send a signal to a control circuit to either start a motor or sorry stop the motor when it overloads and what we mean by overload is it's just using just a little too much current than what it's rated for right and so if we open this access glass little access panel here oops and we can see that this these two contacts here are normally closed right now so that means if we're normal operation these should be closed let's test them and there we go we're getting zero ohms that means we're closed okay now if i simulate the overload of the motor which is pressing this little tab in here to simulate that now it goes in this should measure ol and there it is so that means this normally closed set of contacts with the overload is working properly then we can press that blue button i just pressed and we reset it back to normally operating excellent now be careful about resetting these overloads in the panel these are usually around three phase right 480 volts or 208 circuits so you have to be fully suited up if you ever want to reset these overloads i know it seems uh i know it seems a little bit crazy to have to just suit all up in your arclash gear but you'll be very glad you did if anything bad happened all right so that's really all i wanted to show you on different resistance measurements of different devices so ohms again ol means all the resistance and zero means that we're closed or has very low resistance okay so that's really what we're talking about when it comes to ohm readings now i really want to move on to voltage readings using this meter and in doing so now things have probably shifted for you because you can see me now now what i'm going to do is share my screen yes so i got a good great question coming in i'll be able to answer these uh after the fact as well but you can see on this motor starter here we got l1 to t1 l2 to t2 and l3 to t3 are the ways to test with the meter from top to bottom top to bottom top to bottom great question and we'll be able to answer more at the end okay now let's talk about voltage right that potential difference so our goal is to really understand the potential that's being measured on this black lead and then the potential of the electrons that are measured on this red lead and what are the difference between them so my my first myth and you may have remembered it from the um from the description of this class is does zero voltage mean that our system is de-energized if we measure zero volts in the panel does that mean that our system is dead and we can get to work and that we're safe and the answer is absolutely not right not necessarily right so zero voltage exactly zero voltage means that there's zero potential difference between the two spots you chose right so if you just put the red lead in here and measured something in a panel guess what has nothing to relate it to with this black lead so you're going to measure zero or if you measured the red lead and the black lead on the same phase you didn't realize it was just the same phase let's say the orange or the brown phase or yellow of a 480 volt circuit if it's from the same color to the same color you're going to get a zero voltage potential difference so even though it's as live as can be and you're going to get your shelf seriously hurt or killed inside the cabinet it would still measure zero volts also a meter will measure zero volts if it's on the wrong setting i'm sure we're all guilty of this from time to time if i switched it to dc voltage instead of ac voltage and i went inside a cabinet to measure it's going to give me nothing but zeros because i'm on the wrong setting so be aware of that as well so now i'm going to share my screen with you to a simulated environment so you should now things have shifted around so make sure you can see this screen large so make sure you work things around i'll just give you a second to move your screens around i know things are moving around a lot i want to get get to a lot of fun stuff before we call it a day okay now this is the voltage reading section and let's say this is the panel we're dealing with again we're making the assumption that we're all suited up in our arc flash ppe okay we have proper voltage rated gloves and we have a properly rated meter with the right voltage rating what voltage are we dealing with here from this circuit you can see on the schematic for the circuit again the second most most useful tool we have we have 115 volts ac for this circuit and so that's going to be uh what we use is our baseline to know okay what should the potential difference be in this circuit so here's my meter here i'm going to switch it to does n1 know is it going to be ac or dc it's going to be ac because we see here right ac so i'm going to switch it to ac the squiggly line and we got the red and the black leads here all right so this black lead right it's a good idea to use ground as a reference right for the low potential so let's put that green on ground and then this red one let's drag it over to line now we're seeing 115. now what if i just put that red one in all by itself right we'd measure zero volts because there's nothing to compare it to so you always have to compare one spot to another or what if i did line to line right this thing is going to give us zero volts because again it doesn't matter um it of zero voltage reading doesn't matter and it doesn't say that it's de-energized if we're measuring from the same line to the same line in this case okay so you got to be careful not to do that and be careful so let's go to let's go from line to ground there we go and then let's move this thing around so let's go here still at 115 that means we're at high potential where that red lead is and we've gone down to low potential so what does a voltage difference really mean this is what i like to tell folks when we read a voltage potential between the two leads we can we can tell ourselves that two things are possibly happening between those two leads there's either some work being done right there's some work being done between the two leads in other words the circuit's working properly and let's say the the lights coming on or whatever that's one thing or there's an open circuit between the two leads causing that full voltage where we're dropping off entirely and now we're dead on the other side so in other words a full voltage reading means the circuit's working or the circuit's not working right so that that doesn't really help us narrow it down very much but as you move that high potential lead around a circuit and you see where the voltage goes from 115 to zero suddenly where maybe you didn't expect it to or didn't think it should according to the schematic that's where we found our spot in the electrical troubleshooting so we can go okay 115. we'll do our first check which is 115 here and then 115 here on the other side of this fuse so the load side of this fuse is 115 volts as well we just proved now that the potential of the electrons flowing through this fuse are still high even after the fuse guess what that means the fuse is good the fuse is operating the way it should at least we can say that with a high degree of certainty so we follow these around now let me go to one of these buttons here okay so i'll drag this over to the inlet side of one of these green buttons again this button you press it and these lights come on you see how they came on and you press the off button and they turn off on and off and so we're seeing 115 volts right here on the other side of this button now the way this is now what voltage should i expect to read on the other side of this button will it go to zero or will it stay 115 right well this green button is a normally open button which means it's only going to allow current through when you press it right to start to start a switch so that means if it's high potential on the inside of it or on the incoming side the line side of this button the other side is going to be zero or it should be zero let's find out great it's zero so that means this button is so far looking pretty good but if i press the button what should happen we should energize that other side and be able to see excuse me that those um that we're getting that full voltage potential difference now and there it is 114.8 so within a margin of error of that 115. great turn it off and it should go back to zero there it is so so that's one way to see it and now again we could get that voltage potential all the way up to the light that's really one just fun way to use voltage as we trace through a circuit in in different spots and see where the voltage goes from the full voltage down to zero or if you start getting some weird voltages somewhere between 115 and zero in this case you know what that might mean that might mean that we have some bad wiring now in our circuit that are causing some voltages to get trapped in there especially when we have a bad neutral on the neutral side we end up getting some really strange voltages when we go through on the neutral all right so if we were to measure ohms in here here's one thing we should always be aware of volts you pretty much have to measure on a live circuit right because volts is is the energizing of the electrons so we have to be suited up we have to do this on the live circuit ohms must never be done on a live circuit in fact if i tried to measure ohms now i wouldn't be able to get any good reading it would let me of course the meter lets you do whatever you're going to do with it but a you would not get good readings that would be inaccurate and b since um the meter's not rated to measure live voltage you could actually damage or destroy the meter in or worse hurt yourself in the process by causing an arc flash or some other serious injury so just be careful about measuring resistance inside a panel and if you must measure inside a panel make sure everything is completely de-energized inside that panel all right next thing i'll show you sorry about that is this meter here so we're going to talk amps next right that's the third of the three multi-meter measurement steps here and essentially i'm just going to use this lead to simulate a wire here this meter is measuring it has a clamp here and this clamp really is the amp clamp i'm sure we're all aware of right and this measures um amps right flowing now how has that happened how is that possible that we can measure resistance flowing through this clamp well it's really pretty amazing is that alternating current power ac power and current when it's flowing in a wire like this one produces a magnetic field that's rotating around that wire at all times as it's flowing and when it's not flowing that magnetic field goes away so if we can measure the strength of the magnetic field around this wire when ac current is flowing in it guess what we can measure how much current is flowing in it just by letting this thing crunch the numbers and tell us how much current is flowing so you can basically clamp a wire around make sure it's somewhere near the middle of this clamp usually it doesn't matter they're not too sensitive about that and there's a little chip in here it's it's inside of this clamp and this is basically a little magnetic field detector that's going to tell us and detect how much magnetic field it's sensing and then tell us how many amps it's it's measuring for dc if we're going to measure direct current that's really where we're going to have to install the meter into the circuit so the current actually comes in one side of the meter and comes out the other side on the dc circuit so it's not as easy to measure using magnetic fields on a dc circuit but it is possible to measure current on that dc circuit all right so that's that's really one way to go about it and you can see on this schematic i mean there's so many things you can test in just a simple circuit with two light bulbs right you can you gotta test the relay this r1 relay and make sure it's coil and contacts are good there are you know dozens if not hundreds of control devices that are either open or closed at any given time to run your motors in your facilities or to run your devices in your facilities that there's a lot to test but if you just follow step by step in the schematic from keeping one lead one place and the red lead the other places you can really get to where you want to go quickly so that's really all i wanted to chat with you about so let me just recap here is that get this up for us let me just recap on this right now first and that is zero ohms right means we're closed right from point a to point b that there's solid metal connection so we can never get zero ohms by the way there's no such thing as zero ohms um if you can find a substance or a piece of anything a piece of metal or anything that has zero ohms absolutely zero you might win the nobel prize because we're trying with these superconductors and everything else so your meter probably won't measure a perfect zero but it measure maybe less than five ohms or you know one ohm two ohms half an ohm point one ohm that is a closed circuit that's where we have basically solid metal let's say copper or aluminum or steel between point a and point b oh well great discussion happening on the line about what ol means all all i've seen is open line it's kind of it really depends on the manufacturer they all give different descriptions in their meter uh handbooks and then um it basically means high ohms high amount of resistance there and uh this should be done at the testing component level on a tabletop right for the ohm readings now for the voltage reading again when and where should be in a live circuit live in the panel in the field zero volts means that there's zero potential difference doesn't mean that there's zero energy in that cabinet so be careful about where you're measuring your voltage that's really where it comes into being excuse me it comes into being a qualified person where you know where to measure based on reading the schematic you know what the schematic's telling you you know where to measure and what the readings are going to be when you measure them the thing you always want to make sure of when measuring voltage with a meter is you know you know what you're going to get before you touch those leads down it's never really a good idea to say i wonder what i'm going to get here and go in and actually maybe surpass the ratings of your meter and just blow the thing up so always know what you're supposed to get and whether your meter is rated properly for that job does reading a full voltage mean we're live um not necessarily either i mean it could mean that the uh circuit is operating properly and it's fully live and operational but it could also mean something's wrong and where voltage is dropped off somewhere in that circuit we have to do all arc flash ppe as well when doing voltage whereas ohms we can just do it in our street close or whatever on a tabletop as long as we're completely disconnected from the circuit and then finally amps we use the amp clamp which can do the magic of magnetic fields makes measuring amps on a wire very easy one thing to be wary of with an amp clamp is if you have one wire with current going this way through the amp clamp and another wire with current going the other way going through the amp clamp at the same time you're gonna get zero amps on this on this meter because it's measuring one magnetic field one way and the other the other way let's say the hot and the neutral you're putting them in the same they're going to cancel each other out so be careful about that as well all right now it's time for questions so um let's see what we got we got definitely some good chatter on the chat line i unfortunately won't be able to follow along with all the chat messages but let's see what kind of questions we got here excuse me so um yeah this meter so what model is it this is the proster meter that we're using here for our classroom demonstration purposes we got cm 6000 pro here so c m 6000 pro um yeah sorry about that when the volume cut out early on hopefully you guys heard me uh toward the end of the session here um yes will this available will this be available online later absolutely it will be i'll um i'll be putting it up there our company will be putting it up there about two business days after this session is over does it matter if the red goes on ground and the black goes on the lead that's a great question so in the case of alternating current usually what's happening inside of a wire is that that electrons are just going back and forth right they're vibrating back and forth so black versus red it's highly recommended that you always go black is on the low potential side or the ground and red is on the line side because that that will give you the best readings um it's usually sorry about that yeah sorry about that um so usually the uh the red and black debate really happens when you're on dc where current only flows in one direction and doesn't go back and forth where you could actually get negative or incorrect readings if you're if you switch them around but usually you should still be able to get understandable readings but you want to make sure to best practice go black for low potential and red to higher potential um this presentation will be available yep yep yep um sometimes we just there's so many a great question here is why would we ever need to run two wires at the same time through an amp clamp and that's a great point sometimes we just do it without realizing because there's so many wires inside or we we clamp around a cable right and we don't realize the hot and the neutral are in that same cable that that's why when you put um an amp clamp around a cable that has both hot and neutral in it you're gonna get nothing on it you're like oh you know the cable to this laptop it's not giving me anything and that's because uh that's what it means what does true rms mean great question and what is reading voltage on a fuse meaning the fuse is bad good question so the best most sure i guess foolproof or surefire way to verify that a fuse is good is to be able to safely pull it out of the system when it's fully de-energized pull it out and test it on the tabletop with ohms so if you go from one side of the fuse to the other the best way to 100 verify that that fuse is working properly is if you test across it and you get pretty close to zero ohms right that it's allowing current through it's it's closed if you test across a fuse and you get ol that means the fuse is bad that's the best way to verify now using voltage testing can get you to really see whether that's happening because we're going live live live and then we go to the other side of the fuse and it's dead so we went from 115 and then on the other side of the fuse went to zero even though this should be working properly that's what starts telling you okay something's going on with that fuse that's really where voltage can start helping us zero in quickly on where where to look and what to verify always check the component that you're about to replace with ohms before you throw it away and before you replace it just to verify right using what we talked about today what does true rms mean great question so voltage in an alternating current is actually going up and down 60 times every second right in the united states or 50 times a second 50 hertz in the uk and other countries going up and down 60 times a second so does that mean that the reading of the voltage on an ac circuit is going to go up and down 60 times a second not necessarily right what's actually happening is the meter is taking the rms which is the root mean squared it's a calculation that gives basically an average you know a weighted average i guess you could say of the of the voltage level as it fluctuates up and down positive negative back and forth and so 120 is actually a root mean square value it's a average so this thing's actually going up to i want to say one 140 or so if you do all the calculations it's going up to positive higher volts and negative but it's all adds up and kind of averages out to the rms value of 120 or 115 or 480 volts okay so that's really what rms tends to mean and that's really what these meters tend to tell you is the rms value which we all understand is the value of current of the voltage that we want to know great questions here um let's see how much time i got to answer them i'll try to be here as long as possible i got maybe five or ten more minutes we can spend let's see does this meter have a hold button it absolutely does there's a hold button right in the middle bottom here and what this does is it it can hold whatever reading you had last where it'll basically say all right um it's fluctuating a lot but here's here's where it was when you press the hold button it's going to tell you a consistent value that you can show to others or you can you can take a look to understand if it's fluctuating a lot okay good um so let's see one cable meter is capable of measuring rms voltage versus meters that are not capable of measuring rms voltage um pretty much any meter i've seen really is measuring rms usually what we see is uh like at the fine level of these higher higher level oscilloscopes and that kind of thing where they're actually able to show you the wave form and what it's looking like we're at that at that individual might you know fraction of a second level um those are you know looking at actual voltage um power quality testing is really where it starts to get into okay what's the wave looking like is it higher power quality or lower power quality that kind of stuff um how much noise is in the system that that gets to higher tech equipment but generally a typical multimeter that we use in our job as electricians are giving us the rms value uh see good i like that so um we have an idea here it says um when they're teaching the idea that this individual is teaching uh the idea of open versus closed um that same line voltage effect if you're getting a reading means the circuit is open right and if you get a zero then it means you have a good path and that's that's certainly true um where you could be measuring one point of a let's say a path from one part of the panel to another through a wire and if you get a zero voltage potential difference guess what that means the path is good the real issue comes what if you get like two volts right what if you have a three volt three volts what does that mean about that path that's really where um that's really where ohms will tell us more of the complete story this recording will be available yep yep yep it will be about two business days after this session is over um let's see great question so it's i kind of hinted at this before but let's talk about it a little bit when you switch the red and black leads on a meter you see a negative value on dc whereas you flip them the um you flip them around in ac and you don't get a negative value why is that and that is because ac already uh alternating current already is fluctuating from positive to negative positive to negative so basically current is flowing one direction stopping and then flowing in the other direction and stopping and it's doing that 60 times every second back and forth back and forth so the signal is actually going from plus to minus plus to minus plus to minus plus to minus 60 times every second really fast so what we're doing is just we're getting that rms value which is a positive value no matter which way you slice it of okay 120 volts as it goes like this up and down that's what we're going to tell you so really negative isn't a thing until you talk about dc which direct current is electrons are flowing in one direction and they keep going all the way into the load let's say the light bulb and then they flow all the way back on the neutral back to the battery or other dc power source so that's just flowing all around the circuit in one way it's not turning back right it's not really going back it's going forward and that's why we use diodes right if you're all familiar with diodes where they allow current in one direction but not backwards right it's like a check valve but for but for electricity um that really is a way to turn ac into dc so you'll see when you look at converters or rectifiers that they have diodes in there to turn the ac that wants to go back and forth just to let it go forth fourth fourth fourth fourth and forward again can you discharge a capacitor with a multimeter great question so we highly recommend that you use a properly rated capacitor discharge device to discharge a capacitor and what is not an example of that is a screwdriver right or passing it to your co-worker to throw a prank on them right that's not a good example of discharging a capacitor some of these can pump out the short burst of electrons uh to the point where they can hurt someone or kill someone right so you got to be careful of that um can certain meters have a ability to have a rated capacitor discharge device inside them absolutely for sure that is possible there's all sorts of different shapes and sizes of meters out there see why sometimes when i'm measuring 480 volts it gives me 500 until which values measuring are are they good so is it okay to have 500 volts on a 480 volt system well depends on the manufacturer of the equipment that you are using so this general standard is you never want to go higher or lower than about three to five percent of the total voltage rating higher or lower than the rated or what we call nominal voltage rating of 480. so if if you crunch that out right that's you know 40 that's 20 right volts or so um yeah that's about right 20 volts swing in any direction so you're right at that cusp where that voltage surge or swing could be caused by some issues in your circuit so if you're starting to regularly measure 500 that's that's getting to be in dangerous territory as far as i'm concerned but again i can't be the expert on it until i really see your facility but definitely talk to our instructors about it if you're ever in the classroom over the next several months we can talk in more detail about that it's a great question should fuses be measured in ohms or ac great question i say measure ohms but the only way to do that is for you to unfortunately spend time in blocking out tagging out uh completely de-energizing the circuit making sure with your meter that we got zero volts everywhere across all three phase to phase to phase and phase to ground face to ground face to ground then we can pull the fuses out and measure them on a tabletop that's the best most surefire way to know whether the fuse is good or bad but if you don't have that ability right now again you have to still so if you're going to measure with live voltage the key is you never want to test top to bottom of the same fuse okay that's that's really not a good recommended way because if that fuse is bad in the fuse blue because because it experienced let's say 10 000 amps of electricity that caused it to blow in a short circuit situation guess what the fuse becomes now if you go from top to bottom of that fuse holder it's your meter and the meter could actually blow up in your hands and do these things pack a punch if they blow up and are not properly rated for the job absolutely so um meters that are properly rated for the correct category of the work you're doing should not catastrophically blow up they'll definitely fail but they won't hurt they won't destroy you or your hands or your face or whatever if they're properly rated category they they can withstand the types of short circuit currents in this in the situations we're dealing with so for um in terms of categories right for industrial electrical work we at tpc training say never settle for less than category three so there's only four categories category three is for any industrial you know three-phase motors and control circuit type of work and category 4 is anytime you step outdoors you should you should be category 4 for these meters is there a standard method for troubleshooting you know what that's a great question there is not one surefire way to troubleshoot i'm sure if you ask one technician one way um on how they'd fix up issue it'll be different in ever so slightly different ways from how another technician solves an issue however um tpc we you know through all the research we've done in our different troubleshooting courses and coursework we really do have a framework around proper troubleshooting and feel free to you know um give us a call after this you see the phone number here and we can tell you more about it but basically it's the it's it's about like an eight-step process right where you start by asking the right questions and by using your senses just like we talked about today and then you can start using your measurement device from there and you have to be systematic about that and then from there one thing i always recommend you guys do if you're troubleshooting is don't what's the word don't ignore or don't mistreat i guess could say the machine operator right so the people who are actually operating the equipment day in and day out that you need to fix they know if they're a wealth of information and try not to push the machine operator or the equipment operator out of the way and just try to troubleshoot by yourself they've seen they've heard they've smelled they've seen what's been going on and um they can probably you can probably figure out what's wrong more times than not just by listening and asking the right questions of the equipment operators okay great question um let's see a lower than expected voltage what does that mean so let's say i measured across line to neutral and i got you know 100 volts or 105 volts right there is there's been a voltage drop somewhere right and so a lot of times this can happen if um let's say our main panel that was providing us 120 volts was a half a mile away like on the other side of a warehouse facility and then we ran the conduit all the way nonstop from that panel all the way over to the other side of the building just the length of that wire let's say thousands of foot of copper wire whatever size it might be has has what we call a resistance that's built up over the course of that wire so by the time it gets to your panel and you measure line and neutral in the panel just like we did earlier it might not give you 120 it'll probably give you you know 110 105 depending on how long that run of wire was so you have to be careful about distance and whether you need to boost the voltage back up through some sort of transformer before it gets to these panels also low voltages could be all sorts of issues around um your power quality and the the cleanliness i guess you could say how clean um your power signal is if there's a lot of motors running or a huge motor is kicking on in your facility it can actually drop the voltage uh coming to let's say your lights that's why some of us when we're in our homes we turn on the microwave or turn on a space heater and the lights dim a little bit that's a that's a lower voltage for a period of time while something else is causing a big disturbance in the system um i don't have time to answer everything unfortunately but i'm going to try my best here to answer just one or two more okay and then we'll call it a day let's see um great question this is a great clarity here a safety issue you all need to be aware of is make sure you hold make sure the hold button is not activated that it's turned off before checking voltage because if you accidentally have the whole button activated on a zero and you're measuring voltage it's on hold it's going to keep showing zero and you could trick yourself into thinking the circuit is dead great point there oh this is a good question we didn't quite get into the idea of meg ohm meters right meg if anyone's familiar with those uh acronyms we use you know mega mega ohm meter um how many ohms is a mega ohm that is 1 million ohms so there are ohm meters out there that measure mega ohms now what is a mega meter what's the usefulness of measuring a million ohms right this these mega meters and this one actually can measure mega ohms if i measured in the right spot it's really useful to measure mega ohms on devices where we wonder whether the wiring that's in them let's say a motor or a switch gear or a panel is not making contact with the metal enclosure that it's in or the motor housing that it's in so if you have let's say three phase motors coils of motors inside a motor or a of coils inside a motor and you test one lead of your mega ohm meter is going to be on the coil of the motor and the other lead is going to be on the metal housing of that motor let's say a screw terminal that's there there should be no connection between live leads that are normally live and and the housing and if we even read 5 million ohms right or 4 million ohms guess what that's low enough that we could start seeing just slight leakages of current from the live leads so um think about this and write this down if you ever want to get more information there's a there's a book by the nfpa i'm sure we're aware of nfpa 70 the national electrical code and nfpa 70e the arc flash safety that standard for electrical safety in the workplace which is coming out new this year by the way the third one is nfpa 70b as in boy and fpa70b is the uh electrical equipment maintenance standard and that gives us uh how many of those how many mega ohms a piece of equipment let's say rotating equipment like a motor or switch gear like a stationary equipment should read if um it's properly operating according to the standard and that's somewhere around five mega ohms last i checked um where if we're reading five mega ohms or less we need to start taking some action to fix this thing before let's say the installation on that wire breaks down to the point where we're going gonna have a ground fault all right let's see um great so some people talk about their categories here and that's a great thing to so if you're working on three phase and you have a category two i say it's time to put that meter away talk to your employer your boss your supervisor because category two is only rated for branch circuits at 120 and 240 volts like in a home or a hotel or something in the commercial side if you're dealing with three-phase circuits um with motors and that kind of thing category three is the way to go so definitely keep that in mind it's kind of an industry standard out there when it comes to the four categories of meters and again that name of that book i was referencing is nfpa 70b as in boy and absolutely to close us out is is using a meter risky in fact i need you to understand the seriousness of using a multimeter you can't just walk up in your shorts and t-shirt and measure something with a meter including unfortunately your own light sockets in your homes right this meter is touching when we're measuring voltage it's touching live electrical circuits and the only thing between all that current and voltage potential coming out at you is this little meter here so this thing really you have to make sure you're understanding how it works that you're using it properly within its specifications and that you are very systematic about where you're choosing to test based on your understanding of the system as a qualified electrical worker thank you all so much for your curious questions and i really appreciate you being here thank you again for being here and have a wonderful day everyone

Channel: TPC Training

Views: 71,724

Rating: 4.934876 out of 5

Keywords: tpc training, electrical troubleshooting, multimeter readings, ac voltage, dc voltage, electrical training, ohm reading, ampere reading

Id: MJsTpQgGFKc

Length: 58min 1sec (3481 seconds)

Published: Thu Aug 06 2020