How to Test for Resistance? What is Continuity?
Вставка
- Опубліковано 21 лют 2023
- Join this channel to get access to perks:
/ @electricianu
Most electricians know how to use our meters to troubleshoot power issues by finding voltage and amperage. But what about using them to find Ohms or Continuity? And what are those values good for? In todays episode of Electrician U, Dustin explains how to use your meter to get these values and what those values could be used for in the field.
🤘⚡️MEMBERSHIP⚡️🤘
JOIN ELECTRICIAN U - become a member and get:
FREE Continuing Education every year
FREE Practice Exams
FREE Monthly Video Courses
FREE Weekly Live Instructor-Led Classes
FREE Monthly Educational Newsletter
Premium Members-Only Content
Private Discord Channel
Monthly Members-Only Discord Chats
Sign up here --- www.electricianu.com/electric...
🎧🎹MUSIC AND VIDEO:🎹🎧
/ descantmv
🎬✍️ART AND ILLUSTRATION:✍️🎬
www.daverussoart.com
First, be aware that different meters will produce different value ranges. Most electricians in the field don’t carry our DMM (digital multi meters) with us everywhere. They are rather large and susceptible to damage, so are usually kept in the truck. Instead, we probably will have our Ampere Meter with us. An amp meter may read in thousandths of ohms whereas a DMM may read exactly what the ohms are. Something to keep in mind. Also, when using your DMM, make sure you are following the instructions for your particular meter and plug the leads in the correct ports on the meter. And finally, when using your DMM OR Amp Meter, do not check for continuity on an energized circuit. Most meters are fused to protect themselves, but checking for continuity or Ohms on an energized circuit will certainly blow that fuse.
Some meters will have the continuity and resistance setting at the same place on the dial. Some are different settings. For continuity, look for the little speaker symbol. For ohms specifically, look for the Ohms symbol (or the Greek letter for Omega) which looks sort of like an inverted horseshoe. To check for either continuity or Ohms on either meter, simply turn the dial to the setting you want and place one lead on one end of the wire (or whatever you are testing) and one on the other. If your meter howls at you, it is sensing that a complete loop has been made. If the meter is on Ohms vs Continuity the meter should display the amount of ohms worth of resistance.
But what are those values good for out in the field? Well, you could use the continuity setting to see if a fuse or filament type lamp (not a CFL) is good. Put one lead on each end and if there is continuity, then the fuse is viable (or the lamp is good). Or maybe you need to run wire to a piece of heating equipment that isn’t labeled as to its amperage. You could test across the heating element to see how much resistance it holds. Then using Ohms law, you can figure out how many amps it will draw and then you can base your wire size upon that. So, for instance if you had a 240 piece of equipment with a heating element of 5.77 ohms, by applying Ohms Law (Amps=Voltage Divided by Resistance) you will see that the equipment will draw 41.6 amps (plus any other items within the equipment like a blower motor).
Another nifty veteran trick (its not really a trick!) to use resistance for is to check wire length. In Chapter 9 Table 8 of the NEC, it lists the specific Ohms for different types of wire. Simply pick the wire type you will be checking (the table has both solid and stranded- solid wire shows a quantity of 1 and stranded has all the others), coated or uncoated and aluminum or copper. The table shows the value per 1000’ of conductor. So say you have a roll of #12 wire in the shop and you need about 250’ for a run you are pulling. Simply put one lead on one end of the rolled-up wire and the other lead on the opposite end of the wire. 1000’ of #12 should be about 2 ohms worth of resistance. So an entire 500’ roll of #12 should read about 1 ohm and half a roll about .5 ohms. Super useful. You can also pull the same prank on wires that are installed. If you had a 120v pole light installed and needed to know the length of the run, with the POWER OFF, tie 2 of the 3 conductors together (say the hot and the neutral) at the pole, disconnect the wires from the breaker/bus bars and take an Ohms reading. Divide the value it gives you by 2 (since you used 2 wires) and bam, you have a length of wire!
We hope this has been helpful in understanding how to take Ohms/continuity readings with your meter and what they could be used for! Is there a topic you would like to see discussed on Electrician U? Leave a comment in the comments section and let us know. Please continue to follow Dustin and Electrician U as we are constantly updating our content to assist our followers in becoming the best electricians that they can be.
#electrician #electrical #electricity #how #to #test #for #resistance #contiuity
As a GC and Plan designer for 40 years, I spend a lot of time in code and best practices, but I do enjoy watching new generations of tradesmen. I remember buying a trade book for $20 to $100 and 90 % of that book I already knew. It was that 10% was worth every bit of the cost. That is why Tradesmen that share on youtube are so valuable. If there is one single learning experience that is a well-watched video.
A couple points you missed. I know that you should "never" do hot work. But just in case you are doing hot work, NEVER (I can't stress this enough) test resistance or continuity on a live circuit. Even if you are working with low voltage wiring or circuit boards. Don't test resistance on live circuits. You will be putting a power supply (the resistance meter) in an unexpected place in the circuit and you could either damage the circuit, cause it to do unexpected things, damage your meter, or any combination of the above. It's also best practice to isolate what you are testing for resistance from the circuit (disconnecting one end is sufficient, but completely removing is often best) so you know you are testing one device instead of everything that might be in parallel to the device. Best case, you get unexpected readings. Worse case, you power something in a way that shouldn't be be powered in that way and you damage it. In power electrical situations you'll probably never damage anything, but in low DC voltage situations (digital sensor inputs, troubleshooting PCBs etc) if you put a reverse voltage on some IC pins, you might damae that pin on the chip causing an even more expensive repair.
Energized work is a legitimate part of the trade, but only when justified, documented, and signed off upon. Just piping up on that one, not to distract from your advice.
@@citygirljace Yeah, that's why I put never in quotation marks. ;-)
Wow! I’m glad you mentioned that. I would have tested on hot wires without thinking about that step.
Thanks!!
Look at me I'm smart and know stuff 🐒
Real talk
This is one of the most helpful videos you've made for me. There's so many electricians out there that know the basics and don't know ohm's law or use it to figure things out. I'd love to see more videos like this! 🤙
Your demonstration of estimating the length of wire on a spool is great. I like how you compared your results with information supplied in Table 8.
Thanks for making these videos. Real Electrical Education and not just entertainment. It's hard to get straight answers about this kinda stuff for some reason.
Thank you. Probably overkill for testing spark plug wires on my truck but still gave me a better understanding. I appreciate the free knowledge. I liked and subscribed
This is a great video even if you know how to use a multimeter, it's still engaging, informative, well delivered and with useful tips and practical uses demonstrated outside of testing. Thumbs up from me 👍
Thank you for this Tutorial.
I understand a lot more now,and you started me on the right path
I just did resistance testing in my pre- apprenticeship. So cool to see this video up. Thanks for your work.
Whats a pre apprenticeship?
@@loanermagic200 here in Australia you can do a 6 month course that covers your first 6 months of technical college before you get an apprenticeship. Most jobs won't consider you unless you've done one.
Great Video, always good to hit the basics sometimes!
Nice video. A common usage for measuring resistance that wasn’t mentioned is to find a good ground location in a car. When using high draw electronics in cars (such as amplifiers) you want a location that has less than .02 ohms to the negative terminal of a battery.
I agree
You are hands down the best electrical instructor on UA-cam, keep up the great content bro 🙌🏽
just got my first personal multimeter, i really appreciate the lesson. the tip about the cable length is handy ill try out some day.
Great video, thanks for the teaching!
Love the videos. Learning a lot!
devil dog, semper fi! i found your channel a few weeks ago, started watching your videos in order then just started skipping around. i watched your "mistakes i've made as an apprentice" and it seems like i'm going down the same path as you haha. i heard you mention in that video you started this career once you left the marines. well i'm 24 and recently left the marines, now i'm joining the army as an interior electrician! no prior knowledge other than your videos, so thanks haha. they're gonna pay me to teach me this stuff, what a steal! anyway, keep up the good work and take it easy.
I love your videos! I pursue anything that helps me be more self-reliant. Great job and keep up the good work
Shh don't say that here, they hate anyone that doesn't pay them for their service
At 5:20 you say that the high ohm bulb "doesn't look like a closed circuit", but the fact that there is a resistance value it IS a closed circuit. If it were an open circuit the meter would have shown OL just like it does when not connected to anything. Different meters have different thresholds where they will sound the continuity beep, read the manual of your specific meter to find out. I'm not sure if the Flukes that I use at work (unfortunately I don't personally one one) would have sounded the continuity tone on that flood lamp.
Also, note that many DMMs aren't in auto range when in continuity mode, so even if the meter shows OL in continuity mode, it may still be a closed circuit with a couple kohms of load. Continuity is primarily used to make sure wires (or wire-like divices such as circuit board traces and fuses) are acting like they should, and to make sure you don't have a short circuit between conductors that shouldn't be connected. That flood lamp giving the continuity tone shows why it is important to isolate what you are testing to make sure you are testing what you expect. For example, if you wanted to make sure there isn't a short in the wiring between a plug and a light socket, having the flood lamp installed in the light socket will give you a continuity tone leading someone who doesn't know to look at the DMM reading to think they have a wiring fault in the plug, socket, or wire. Leading them to waste time trying to find a fault in multiple places where there is none.
Hey, Electrician U, you should gives us a tour of all your Electrical Books.
As always, good video. Thank you.
Thank you for the information, very helpful!
Great video.
Thank you.
P.S. very useful information for us as electricians, we always use it on the job site.
Awesome tip for length of wire.
Great video, as a car mechanic we used to use resistance testing more then anything else. I still use it when working on PCs and stuff.
Hi Dustin. It’s be awesome if you could do a video about different kinds of grounding conductors (EGC,GEC,bonding jumpers,etc.) and how to size them!
I'm pretty sure he already has.
this channel is so great, I get to learn stuff instead of scrolling mindlessl
Thank you sir. Nice explanation.
Very good topic and presentation 🧐
This is so damn cool. I bee. Doing electrical for over ten years in other platforms cand this is really cool how you break it down
Great video... thanks!
👌💯wire measures was a great one💯😁😎
If you have no use for the amperage settings then get one without. That way you only have 1 connection for each lead so you can’t screw that up and damage your multi meter.
I have purchased multimeters for friends. I really like the Uni-t clamp meters. There is only 2 connections for the leads but you can still use the clamp for current.
They have a $50 one that does DC current. Which I think is the least expensive DC clamp meter you can buy.
Very informativr video.
Thano you very much for sharing.
Thank you for this
Thank you !
Good vid as usual ... Thx ...
Awesome video!
Thanks for helping
DUSTIN, try to make a video lesson about different ELEMENTS used in different household appliances and what are the most common ELEMENTS an electrician should know or will troubleshooting the common problems elements cause to go over in a video lesson. Also another vid lesson is to think of the most common applications when an electrician would use Joules Law formulas, because Joules law is HEAT = V * I *TIME, you forget to mention to add in the TIME also into the formula because Wattage = V*I . Try to think of when electricians would use Joules law formulas
This channel is great!
It's definitely helpful for Automotive Diag.
I like this man. He sound professional.
My neighbor was trying to install a new smart thermostat which uses more wires than a standard thermostat. But after wiring it up it blew the fuse on the control board in the furnace.
Eventually we disconnected all the wires at both ends and checked for connectivity between each wire. The blue had connectivity to one of the others. So somewhere along the wire a staple went through the wire and made a connection between 2 of the wires. Shorting them out. Blowing the fuse. So we marked the one that was bad and just used a non standard color for the install.
They had put in a multi wire bundle with a lot of unused colors so that saved us.
This is a perfect example of why not only testing for beeps is important, but also testing for anti-beeps is also important. Good thing to remember not only with bare-ended cabling, but also after wiring connectors and terminal blocks.
Thanks mate, cheers
You do a grat job!
Tank you you are the best tiching l been learn a lot .Tank s to you
Nice1..Electric & thank u
Thanks very interesting
Thanks man 🤙
I always touch test leads together to check the the meter & test leads are in good order.Fir readings under 100 ohms will short the test leads and read the resistance. On old test leads have seen over 4 ohms resistance that you want to subtract.
Good job sir
this guy is awesome
thank you
I’m so happy to see you use a Klein instead of that over priced brand that has less features at 3x the price and doesn’t have the IP rating and is no more safe. Electricians need to have confidence to use a great meter like the Klein;)
I may be wrong but isn't hot resistance (energized circuit) roughly 10 times the reading that you get from a cold reading (de-energized circuit). Is it the reactance that drives up the resistance or does heating the element change it's conductive characteristics?
BTW, love your channel.
No, you are not wrong. You can't measure the resistance of a red hot element when it is cold and make calculations. I am surprised he showed that. That spotlight measure 16 ohms, so per Ohm's law it would draw 7.5 amps. That would be a 900 watt bulb, obviously wrong. It draws that for a small fraction of a second until the filament heats, then drops to 60 watts or so.
@@ianbutler1983 Indeed!
@@ianbutler1983 certain heating wires use nichrome. which has little or no temperature coefficient. this is why the inrush current is so low on many electric heating coils. Here, the author is using an incandescent filament, and not a heating coil. This explains why many electric heaters are nearly 100% efficient, unlike a hot lamp filament, which is nearly 100% efficient at generating thermal heat, but only 1 or 2 % efficient at converting this energy into electromagnetic radiation. 98% efficient heater - 2% efficient visible light source. Much of the heat that is converted to light is in the near-infrared region, anyway, even with lamp filaments running at nearly 3000 Kelvin!
Reactance does not drive up the resistance. The two are two separate parameters.
Resistance applies to DC. Reactance applies to AC. Both are measured in ohms. But they are quite different things.
One does not drive the other.
Do you have a video primarily on Meg Testing?
Could you make a video on converting a 220v circuit to 110v swapping out the 220v circuit breaker with a 110v one. Where would you connect the neutral white from the 220v circuit on the distribution box.
I'm surprised no mention of finding a ground fault or short, with power off, if what should be the live/hot line has continuity to ground (or neutral), proves out a problem. As a landlord, two decades of use, a run of outlets became dead without tripping breaker. Turns out improper ground from old BX cable and continuity between "live" and ground. The electrician decades ago had improperly wired the GFCI downstream as well likely due to that.
Finally❗️a tutorial video where the UA-camr has the exact same multimeter that I have.
Thanks for that 🙏🏾
Makes it easier to follow along
Can you do a video on breaking down high resistance faults with a Megger?
Please discuss "Megaohm" meters (or "Meggers") used for "Insulation Resistance" tests -- such as for a floor heating cable (Schluter) to confirm no leakage from power wire through insulation out to the ground braid -- 1000 volts & more than 1000 ohms Resistance.
They just use high voltages, 250, 500, 1000 volts to see if a current is created.
If the insulation on the cable is performing properly there will be no current.
So the meter is producing a high voltage and measuring the current.
The test current is converted into a voltage inside the meter using a highly accurate resistor and a dual slope integrating analogue to digital converter is used to measure the voltage and convert into binary, and digitally processed for display, hence the test current is measured as the test current and voltage are related by ohms law by use of the accurate resistor.
Simple.
@@deang5622 Thank you - very good
Please do a video on series and parallel circuits. Specifically drawing out real life examples
Serously! That would be Great!
Resistors in series:
RT = R1 + R2 +.....
Resistors in parallel:
1/RT = 1/R1 + 1/R2 +...
And if you have a circuit comprising a mix of both then it's probably easiest to reduce the complexity of circuit by first combining as many series resistors together, replacing those with single effective resistors, and then analyse what remains and combine the resistances in parallel.
Determination of resistance of the length of wire:
For a minute there I thought you were going to explain about resistivity and how to perform the calculation for resistance. I guess that is too much for most electricians to get their head around.
It is after all, how the tables are derived.
wow, im not an electrician but this is cool to know
Please do ground resistance testing next.
Hey dustin, you mentioned in part of your video that multi meters have many functions like testing panels. However when i was testing a panel, i was getting berated by a older electrician saying “you cant use a multi meter to test a panel, that **** never works” and blah blah blah. That “you can only use a wiggy to test a panel” and “iv been doing this for 50+ years” Me still learning i dont see why you couldnt use a DMM. Whats your thoughts??
👍
QUICK-WITTED Electrician U
From Nick Ayivor from London England UK 🇬🇧 ⏰️ 15:46
Hello.
Wish page on the Booker can I found Table 8 Confuctor Properties.
Thank you.
Could you share how you calculate the resistance of a resistor by reading the color bands when they are evenly spaced, and no gold or silver bands appear? I calculate from the end opposite to a gold or silver band, but some resistors do not include a code for tolerance. Another challenge is to distinguished between violet and red when the color appears to be somewhere in between.
I have a question. Lol measuring the ohms for the wire - is it different measuring the ohms to know how much wire you have left if your using larger wire? I'm new to this electrical stuff but definitely curious on your response. Thanks!
Yes, the values shown in chapter 9 table 8 of the National Electrical Code book specify the different values for different gauge wires per 1000 feet
Hey bro, I've always heard that there's a way to ring out cables where the ends are extremely far apart by using TWO multi-meters. Do you know how that's done? Can you explain it?
Please start listing model numbers of tools shown in the video in the Description field. Your video from 1 year ago entitled "4 basic testers" has no model numbers listed and you don't always zoom in to see it
Hey man it would be pretty cool if you do a day in the life of an electrical business owner!!!!
Question..toward the end you used the uncoated copper column however your line you have which you measure has blue insulation. So what does "coated" mean in this instance? I thought uncoated would be bare wire that is not insulated and coated would be insulated. Can anyone help me with this?
Great stuff, as usual. Thanks. You're the teacher I never had as a kid decades ago when I first had a hunger to understand such things. I have to say this, though: I can't "resist" saying that some of what you're showing us is "shocking!" Okay, I know, I know: keep my day job!
Curious, Im a Journeyman Lineman in the IBEW, around 8 years and was wondering how hard would it be if i wanted to swap over to become a licensed electrician? I have been told that my "similar experience" could actually count towards hours you have to have to be able to take the test to get certified. I was really wanting to try this side of electricity out and figure ill take a pay cut at first but could my experience actually count towards getting certified as a electrician?
Depending on your local, you can test in with 10,000+ hours and letters of recommendation. Taking the test and passing doesn't guarantee the rank of AJ, my local offers a residential program and you could take night classes to fill the gap of experience based on your test score or you might get accepted into the apprenticeship at a more experienced class level.
Put that roll of wire in a freezer overnight then again in the hot Sun all day and compare the resistance. The length can vary a lot but there is a formula that takes the temperature into factor also!
Very useful to us as gratuates now😅
With the distance calculation, what if you had broken 4 wire in the ground (pipe or liquid tight or etc) 2 wires of the 4 are damaged and showing continuity between them, that distance calculation should tell you how far away that break is? Ie where to dig to fix the pipe instead of a whole retrench.
This would work? Right? Hypothetically.
Take a known wattage incadescent bulb and measure resistance, do your math ... and wonder.
This is because cold filament has much lower resistance (in my few measurements I got quite consistent value of factor 14) than when being lit. In a way a lamp filament functions as a rapid PTC. So resistance testing is quite useless to deteremine the wattage of lightbulbs (well, maybe, if this factor 14 is really consistent, it can be calculated in?).
I'm not sure how linear heating elements are ...
Why do you use the uninsulated value when the wire on the roll is insulated??
What happened to the video posted recently about testing current? Was it taken down?
Whoa you're right. Wonder what happened
I think that video had a bunch of errors and everybody called him out on them because he made glaring novice mistakes.
It amazes me that you guys don’t use testers like the Fluke 1664. Uk and Europe it’s a require piece of kit to be an electrician, together with a thorough understanding of testing.
That is a $2500 or so tester..........
@@jimmyPOUFAJones yep, and that’s a cheaper model. All sparks in the UK have one or similar. Plus testers like the fluke T150 and a torque screwdriver… the list goes on…
Sir good morning
He Dustin, I’ve been told that being an electrician takes a toll of on your body… I like doing the work though, I’d just like to still be able to walk and maneuver around when I have kids with no problem. With this being said do you think I switch careers? I have friends that are car salesmen and are making really good money but I WANT MORE in life. I think about electrical contracting BUSINESS and they are on a totally different page than I am. It’s cool if you don’t respond I’m just in a hole right now so anyone who has any input let me know! Thanks in advance
I didn't think "amperage" was a word!!
Most normal multimeters measure resistance with about 1 mA current. It's too low for many things outside your lab table. At least that wire length measurement would get you easily way off. For better results for low resistances you could use an installation tester at its continuity (or line resistance etc) setting, where the used current would be 200-250 mA. Those often give the result with couple decimal places and you might have an opportunity to zero/compensate your test leads. With basic multimeters you should first test just your leads (should be under 0,2 ohms if not broken and at 0,5 ohms you should get rid of them) and subtract that value from the actual measurement. And be very suspicious in the low end of results, under 2 ohms is hard for most devices.
If you really need to measure some low resistance values, you could use constant current (or otherwise limited output) power supply, that would not die even in total short circuit and measure voltage at a point where you want to get the actual value, so that there isn't any resistance from test setup in your result. I often use 1 amp constant current for things like wire length measurement and other things like that (which is nice, as at 1 amp the measured voltage is directly the resistance in ohms. Other current values need some math.). We even had to measure protective grounding setup in a explosion hazard zone with 10 amps from a adjustable transformer to be sure that every metal part is really grounded and we could get a precise enough result to our report.
tldr: dmm:s give bad results for low resistance, if the result matters, use something with higher test current instead.
Precisely why I carry a standard meter and a clamp on that does mega.
Thank you. I was going to say something similar, but you worded it better than I probably would have.
@@mattfleming86If your clamp-on does mega, wouldn't that be good for very high resistances? Wouldn't you want a milliohm meter for very small resistance values? Or am I getting confused by marketing-speak?
Some have it backwards here. While DMMs aren't that accurate for measuring low resistances like a spool of wire. You want something that is more accurate at low values, not something that can measure in the mega or giga Ohms. An insulation meter ("megger") that measures insulation resistance is a bad choice. A DLRO (digital low ohm resistance ohmeter aka Ductor) is the best choice and some go up to 10A or more. The mutli-function (installation as OP mentioned) testers usually have a low Ohm setting and they work well, as well.
@@mattfleming86 I am not a Electrician I am buying a 220 volt table saw but want to bring it to my job sites which probably All have 120 volt. Is There an equipment bridge that you can recommend I use?
Hello, how to test if a wire is damaged ? Because it keeps my RCBO to trip even with no load. It was working fine, until recently though.
E I R triangle. Such a baby way of representing the ohms law. Haven't used that since I was 12 years old.
At your level of expertise you should be able to remember one form of the equation and be able to re-arrange it when required.
Realy hope someone can help me.
When i test a armature commutator i set multimeter to 20M ohms then 1 wire on shaft and other wire on commutator, then get reading. Is this mean there is a short between ground and commutator?
When set it on lower ohms i not get any reading. Just when set it on 20M ohms and 200M ohms i get reading.
Thank u know I have no more work ,,,
When I measure ohm by fluke, it starts with a big number then goes down to a number. Why it does that? (e.g starts with 315.7 ohm then decrement down to 150 ohm)
👍
Im very new to all of this so Im a little confused. Why does your book say 12 AWG copper should read about 2 ohms but when I look up other books online it claims 1.588 ohms for 12 AWG copper?
yes i would like to know this also? keep the vid's coming brotha!
I used that method on the wire it said I had .4 ohms so I was like wow that's crazy I went to pull the wire it was only 55 ft vs 200ft
So when checking continuity and it shows ol it means the circuit is broken?
I can't wait to use the measuring trick for wire lengths.
How to test for continuity on a 3 way bulb?
Resistance is futile sorry I couldn't resist that. Anyways another cool video
nice :)