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How To Use A Multimeter To Test

Discussion in 'ELECTRICAL ISSUES - POWER YOUR MACHINES & SHOP' started by Nels, Dec 20, 2016.

  1. Nels

    Nels United States Founder Staff Member H-M Supporter-Premium

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    Some of us don't know how to use a multimeter to test for power.

    Can you guys provide an explanation of how to SAFELY test for power?
     
  2. tq60

    tq60 United States Active Member Active Member

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    Power or voltage?

    Way too much to explain to the general question.

    Checking what?

    The short answer is read the instructions that came with the volt meter.

    Next is Google "safe use of multi-meter".

    If you are trying to check a specific thing then ask how to check power on a (describe thing here)

    If you do not know how to use a multi meter do some reading first then practice with a battery or wall wart for voltage and a light bulb for resistance.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk
     
  3. chips&more

    chips&more United States Active User Active Member

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    What kind of multimeter? What kind of power? The probes are typically insulated. Keep your fingers only on the insulated part. Set-up the meter correctly so you don’t smoke it. Very high voltage is a different animal/story.
     
  4. Nels

    Nels United States Founder Staff Member H-M Supporter-Premium

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    I want to test for 110 using a small sperry handheld I have. The instructions are in 6 point type!

    I also want to test on 220 machines if possible.

    Here is the cheap one I own:

    41EXf-0qupL._SY400_.jpg
     
    Last edited: Dec 22, 2016
  5. RandyM

    RandyM United States Global Moderator Staff Member H-M Supporter-Premium

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  6. markba633csi

    markba633csi United States Active Member Active Member

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    Main idea is to set it to a range higher than what you are expecting to read, unless it is auto-ranging. Analog meters (with a needle) are often better for some tests like intermittants, and they are more rugged electrically than digital meters, important for sparky- motory type stuff.
    Most cheap meters have poor probes/test leads, too short and with points not sharp enough to penetrate varnish and corrosion.
    I like probes that can accept screw-on alligator clips, very handy and safer.
    Mark S.
     
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  7. CluelessNewB

    CluelessNewB Active Resistor H-M Supporter-Premium

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    There are several YouTube videos on how to use a multimeter you might want to check out.
     
  8. higgite

    higgite General Manger - Proofreading Dept. Active Member

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  9. jim18655

    jim18655 United States Active User H-M Supporter-Premium

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    A few things to keep in mind:

    1. Check meter on a known source before you touch a "dead" wire. Make sure the meter will handle the expected voltage. I've seen some meters the max out at about 300 volts and it may not turn out well for you if you're reading 480 volts. Wear safety glasses when working on live equipment. Things happen and metal burns and is faster than you can blink.
    2. Don't rotate dial while the leads are attached to a power source. Depending on the type/brand of meter you could rotate through the ohms or current setting and best case blow an internal fuse or blow the meter up.
    3. Current is measured with the meter inline so it is basically a short circuit if you were to attach to a voltage source. See #2 for the results.
    4. Test for power BEFORE you check resistance or continuity. Check both AC and DC if you're not sure what your source is. Once again see #2.
    5. We like to think our machines are properly grounded but it may not be the case. If you can't get a reading to ground then check phase to phase to be sure you're getting an accurate reading.
     
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  10. tq60

    tq60 United States Active Member Active Member

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    Reminder. ..

    Always do this!

    If measuring any type of current REMOVE THE LEADS FROM METER AND RECONFIGURE FOR VOLTS!

    As mentioned above when measuring current or amps most non - clamping meters are in series and are same as a clip lead or wire.

    Meters usually have a dedicated socket (s) for measuring amps ( some do not)

    Many folks at all skill levels at one time or another will forget to move the lead from current (meter is a clip lead or short circuit) back to non - current configuration (high impedance or like open circuit) and go to measure a voltage resulting in blown fuse and damaged equipment before you see the spark.

    Get in the habit of moving the wire as soon as finished.

    Sent from my SAMSUNG-SGH-I337Z using Tapatalk
     
    Last edited by a moderator: Dec 21, 2016
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  11. 4gsr

    4gsr Global Moderator Staff Member H-M Supporter-Premium

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    Yeah? I bet the gills flutter a little bit too!
     
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  12. British Steel

    British Steel United Kingdom Active User Active Member

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    Also, when testing power, if one clip falls off DON'T make a grab for it while the other's still connected...

    Dave "50-cycle jitterbug" H. (the other one)
     
  13. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    In keeping with our usual practice, I think Nelson wants us to tell him how WE use our meters, not just send him somewhere to watch videos. We're here to teach each other, and there is probably more trust in what our members tell or show him than simply refer him to someone else. If we did nothing but point out what NOT to do, preferably with pictures, as always, that would mean more to him. Besides, this is interactive instead of just watching an infomercial by Fluke.
     
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  14. markba633csi

    markba633csi United States Active Member Active Member

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    At one company I worked at in the 70s we had some real "gifted" people. I watched one such brainiac take a brand-new 300$ Simpson digital voltmeter out of the box, and try to measure an 1800 volt transformer. It literally caught on fire and burned like a roman candle. Max AC rating was 700 volts I think. It was an interesting place, lots of high voltage and Van Halen!
    MS
     
  15. jim18655

    jim18655 United States Active User H-M Supporter-Premium

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    Sometime measuring is the easy part. Understanding what you get is the hard part. Your typical 240 volt single phase machine should be about 1/2 of the system voltage or 120 volts to ground or neutral. 3 phase is a different animal altogether. The voltage between phases should be close to system voltage. You can have 120/208, 120/240 and 277/480. The first number is the voltage you should read to ground and the second number is hot to hot. The 120/240 3 phase delta will have a high or wild leg that will be about 200 volts to ground but 240 to any other hot leg. All of these voltages can vary about 10% and still be in spec for the system.
    When checking fuses go top to bottom on the fuse and a good fuse will read 0 volts with the switch on. Think of placing your leads on the same wire several inches apart. There won't be a voltage drop to read. Bad fuses will read the higher voltage of your system voltage so a 120/240 system will have 240 volts top to bottom of the fuse if the device is a 2 pole switch. A single pole switch will be 120 volts top to bottom. The same procedure can be used to check if a switch or contact is closed (on). An open switch or contact will read the voltage applied to the switch. The light switch in your wall will be 120 volts if off and 0 volts across the terminals if on.
    Continuity or resistance will show if you are connected to the same wire with both probes. Typical digital meters will display OL if the probes are not on the same wire. Turn your meter to the ohm symbol and see what the meter displays when the probes aren't touching and then you'll know what to look for on the display. Touch the probes together and it should display a number close to zero. That is the indication your probes are on the same wire or that a fuse is good. Make sure when you check fuses with an ohm meter that the circuit is off ( see previous post) or pull the fuse and check it out of the circuit. Don't lay it on a metal surface when you check it or it will show good every time. Yes, I've seen "pros" make that mistake.
    Read your book for the meter because some default to AC and some to DC when you turn them on. Trying to read the wrong type will give you the wrong reading and could be dangerous. Make sure you're on the proper setting before you start. Play with reading batteries and practice checking continuity on wires and cords. Check the resistance of different light bulbs. You can even check the resistance from hand to hand. Now lick your fingers and grip the probes and see how much lower the resistance goes and you'll see why standing in water while using tools isn't good.

    Be careful trying to read the output of a VFD because it isn't a true sine wave and some meters can't display the voltage properly.
    Hope this helps.
     
    Last edited: Dec 20, 2016
  16. Subwayrocket

    Subwayrocket United States H-M Supporter - Premium Content H-M Supporter-Premium

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    Before doing anything, first make sure you've got good batteries in it . I always start with a continuity test before doing anything else .
    Do this by setting the meter to the lowest "Ohms"setting and touch the probes together...the meter should beep or jump to zero ohms reading.
    At that point you know you've got good cables and probes.

    I advise you If u don't know how to use a multimeter, don't try to learn on energized live circuits. Watch a few videos as stated above, make sure you understand what you're doing lest u damage the meter , short the equipment or injure yourself.

    To check for 110 VAC or 220 VAC , set it for "Volts AC" (VAC) , the meter may be labeled V~ , then set it to a range that what you're testing falls into.
    Basically you don't test for 220 vac on the 0-30 VAC setting . Then hold the probes across the terminals or outlet.

    ----------------------------------------------------------------------------------------------------------------------------------------------------------
    Ohms symbol, meter reades "open circuit" , infinite ohms
    1Ohms.jpg
    --------------------

    Doing a Continuity test, meter reads almost zero ohms, little to no resistance

    2Continuity.jpg
    --------------------



    AC volts symbol, for 110vac or 220vac

    3VAC.jpg
    --------------------


    DC Volts symbol

    4VDC.jpg
     
    Last edited: Dec 20, 2016
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  17. dieselshadow

    dieselshadow United States Do you smell something? H-M Supporter-Premium

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    Always check a known source of power like a power outlet that is working before testing a circuit that you believe is dead or de-energized. Then after using the meter, re-confirm the meter is good by checking the same known power source. If you do not get a good reading, you must investigate to find out if you measured it wrong or your meter isn't telling you the truth.

    Only after proving the meter, check known grounds and prove new grounds using the meter. Only after testing a ground can you call it a known ground. If a machine isn't grounded properly, not only does it pose a serious safety (electrocution) hazard, but can pose electrical issue along with some crazy diagnostics. Prove the ground before doing any real work with a machine or doing any electrical work on it. It could save you life.
     
  18. wa5cab

    wa5cab Downloads Moderator Staff Member H-M Supporter-Premium

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    Also, before doing most of the above, learn the electrical standards for your area, both today if you are running a new circuit and around the time that the circuit or system that you are working on was built. Standard practices at least in the USA have changed significantly several times since around 1900.

    Current practice most of the USA is that residential power at the meter is nominally 120/240 VAC single phase. This means that you can have two 120 VAC supplies and one 240 VAC supply. Going back in time you find that the "standard" or nominal voltages in the system were 117/234. 115/230 and 110/220. What you can actually have today can go as high as about 125/250 depending upon loads, time of day, time of year, etc. This is today a 4-wire system, with the four wires being named Ground, Neutral, Line 1 and Line 2.

    General practice today is that all distribution cables except for wires running only to switches will be three wires for 120 circuits and four wires for 240 circuits. Color codes for the wire insulation for 120 volt circuits are either bare copper or Green for Ground, White for Neutral and Black for either Line 1 or Line 2. In 240 (only) circuits there will be bare copper or Green for Ground, Black for Line 1 and Red for Line 2. For 120/240 circuits, the same plus White for Neutral. Wires run only to a switch may be bare copper for Ground, and White and Black for the other two. AFAIK, there is no standard for which of the two colors to a switch is still hot with the switch OFF. And don't just assume (switches aside) that any white wire is safe to touch. Electricians can be as competent or incompetent as any other trade.

    Local electrical codes can vary, but in most, Ground and Neutral are connected together only at the electrical service entry panel or sometimes only at the meter in jurisdictions were the code allows the entry panel and the meter to be in separate locations. Houston happens to require the entry panel to be near the meter on an exterior wall of the building. From what I've seen around the USA, that's unusual. In any case, past the entry panel the neutral and ground wires (if both are present) are generally separate and not allowed to be mechanically connected.

    It is possible to get a non-zero volts reading between Ground and Neutral. This could happen for example with a large motor running on 120 VAC fed with wire that isn't quite large enough. The true voltage being applied to the motor would be that between the White and Black wires. But the voltage being applied to you if you are dumb enough to touch the black wire would be slightly higher because you would be putting yourself between Line and Ground, not Line and Neutral. And at the instant before you touched the Black wire, there would have been no current flowing in the Ground wire. The voltage differential between Neutral and Ground probably won't hurt you but play it safe and don't touch the White wire either.
     
  19. David S

    David S Canada Active User H-M Supporter-Premium

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    Just to add to Robert's post. Regarding the number of wires for 120 vs 240 circuits. While in residential applications things like ranges and clothes dryers will be 4 wire 240 volt circuits. Things like water heaters and baseboard heaters are usually 240v 3 wire. At least that is the practice here.

    David
     
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  20. Subwayrocket

    Subwayrocket United States H-M Supporter - Premium Content H-M Supporter-Premium

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    once someone mentions "The code" on a forum , the thread has just "Jumped the Shark" and it's all downhill from there .....Lol
     
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  21. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    Agreed.....the code will vary from location to location and inspector to inspector even. We should stick to teaching how to use a multimeter. Even then, perhaps we should decide whether to go strictly with a digital, or include analog meters. There are advantages and disadvantages to both. Digitals also often are capable of basic tests of capacitors and some semiconductors, whereas analog meters do not offer those.
     
  22. markba633csi

    markba633csi United States Active Member Active Member

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    Agree with Tony; digital and analog meters are different aminals. And, analog meters can do simple go/no go tests even on capacitors and semiconductors.
    Mark S.
     
  23. Nels

    Nels United States Founder Staff Member H-M Supporter-Premium

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    Here is the cheap one I have:

    41EXf-0qupL._SY400_.jpg



    After I get the hang of it, I will move up to a better one. Are there fused models, so that if I smoke it I can replace a fuse?
     
  24. Nels

    Nels United States Founder Staff Member H-M Supporter-Premium

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    Correct Tony. Show me what YOU guys do, for example to check a motor with one , check your wiring on a VFD, check for continuity on a lathe or mill.
     
  25. Nels

    Nels United States Founder Staff Member H-M Supporter-Premium

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  26. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    I wouldn't spend the money on a tossmeter, but when you get a good meter, a lifer, spend the money on good probes. My favorites, and I'm sure every serious meter user has theirs, are those from Oldaker. They make aftermarket probes that are very good. Especially if you like or need the insulation piercing type. Pamona also makes great test leads, but I have grown attached to my Oldakers.

    http://www.testleads.net/

    no connection other than a very satisfied customer
     
  27. chips&more

    chips&more United States Active User Active Member

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    For me personally, I would only want a Fluke brand mulitimeter. And yes they are internally fused. I find used Flukes at my local fleamarket all the time. And have had VERY good luck with them still working. They are very reliable. A few with a blown fuse, dirty or broken female pin sockets and missing display segments. But that’s not common and all fixable. Maybe around $60-$125 for used “current” model Fluke mulitimeter. Do not get the older all gray cased models. And only get it with the original Fluke probes/wires (that have not been spark tested:eek 2:)…Good Luck, Dave
     
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  28. hman

    hman Active User H-M Supporter-Premium

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    Nels -
    I'd be willing to betcha anything that your meter is indeed internally fused. Shucks, even the Harbor Freight giveaway meters have a fuse inside. You can find it by removing the back cover (not just the battery cover). And don't sweat that you don't have a Cadillac class meter. Any multimeter that can find AC and CD voltages and resistances can be used to diagnose a motor. I do own a good Tektronics meter, but use a Harbor Freight giveaway for most of what I do. And of course, once you get started with the meter you have, you can draw your own conclusions about upgrading.

    Disclaimer - I haven't looked at the videos, so I may be terribly redundant here ... but then again, we're talking about some pretty basic stuff.

    First, be SURE the motor is isolated from all possible sources of power. Then use a screwdriver or something else with an insulated handle to short across any capacitors.

    Switch to a resistance (ohm, Ω) scale. For simple shorts testing, the highest scale is best. For checking windings & continuity, use the lowest scale. Some meters are auto-ranging, so just set to ohms.

    SHORTS
    Set the meter to the highest available scale. Note what indication the meter gives when the test leads are not in contact, so you'll recognize it during testing. We'll call this "infinite resistance."

    Now hold both leads against a bare metal part of the motor frame. You should see something like zero resistance. If not, you may need to scrape through paint, clear lacquer, or crud to make good contact with the metal.

    Keep one lead against the metal (or even better, held in place under the head of a screw). Now touch it to each the wires and terminals you can find. You should NOT see zero or small values of resistance anywhere. If so, you have a dangerous short to ground.

    Capacitors can be given a very basic "proof of life" test (AFTER THEY'VE BEEN SHORTED to be sure there's no high voltage juice left inside). Place the test leads across the terminals. A good capacitor will very briefly show a somewhat low resistance, then go up to infinite resistance. What you're seeing is the test current from the meter charging up the capacitor. As the capacitor is charged, it no longer accepts current. No current flowing in the leads = high resistance. You can repeat the test a few times by shorting out the capacitor between tests.

    OPENS/CONTINUITY
    Set to a low resistance scale. Hold both leads together. Note the indicated resistance. It should be a small value or zero. If not zero, this indicates the resistance of the leads and internal stuff in the meter. Note this "lead resistance" for later reference. If far from zero, something is wrong.

    Now touch the leads across the ends of the various coils of the motor field. This is best done after disconnecting all wires from their terminals (you DID draw a diagram of what went where, didn't you?), so that you're looking at just one coil at a time. You should get relatively small resistance values (couple ohms at most). If necessary, you can "correct" these readings by subtracting the previously measured lead resistance. Lower quality meters will also have a random factor in the equation, but you can usually get a good approximation of what's going on. Run coils may well have different resistances than start coils, etc.

    If the motor has a centrifugal switch, check the resistance across it, both with the switch closed and with it (manually) opened.

    Brush-type motors can be given a few additional tests. Check the brushes themselves by placing the leads on the wire leading to the brush and on the commutator segment the brush is touching. You can check the rotor windings by connecting the test leads from one brush wire to the other and slowly rotating the rotor, so that all pairs of commutators are connected in turn. Resistance should be low, but will vary a bit when the brushes are "between" commutator segments.

    Knowing how the motor is wired is, of course, very helpful (or let's call it absolutely necessary) for interpreting what you find.

    I haven't even touched on the voltage scales, have I? This is probably well covered in the videos. If not, just ask for clarification.
     
  29. Tony Wells

    Tony Wells United States Vice President Staff Member Administrator

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    This is probably a good approach. Take each basic function of a meter (consider just a plain jane DMM) and one at a time, let's talk about everything you can think of that you can do with that basic function. It's going to get far too confusing to jump from measuring continuity (actually different than resistance with some meters), then move to voltage checks, breaking them into AC and DC, then on to current measurement, and so on. A little structure will make this much easier to understand. We who use meters quite a bit might follow along just fine, but for a basic instruction breakin, let's keep the topic limited to one at a time. If they overlap, let's allude to that and save it for the last when we can talk about special uses.
     
  30. wudwlkr

    wudwlkr Iron Registered Member

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    Hard to tell from the photograph of your meter but it does not look like it has a current measuring function, mA or A, on the dial. Do not attempt to measure current with this meter. One of the basic requirements to using a meter is to understand the difference between parallel connections and series connections. Voltage is always done with a parallel connection and current is done with a series connection. When measuring voltage you simply connect one lead to one test point and the other lead to a known common or ground thus placing the meter across or in parallel with the circuit or device being measured. To measure current you have to put an opening in the circuit and connect the meter between the two open points thus placing the meter in series with the circuit. Why this is important is that in a parallel connection, because of the high internal resistance of the meter, only a very small amount of current will flow through the meter itself so it is safe to handle. In a series connection all the current in the circuit will also flow through the meter. If there is a short in the circuit being tested then all the fault current will also try to flow through the meter resulting in a damaged meter and possibly an exploding bomb in your face. Better multimeters will have separate low current, usually marked mA (milliAmps), and high current, marked A (Amperes), inputs. These will usually both be separately fused inside the meter to provide protection. These fuses are usually a buss type fuse but with really oddball ratings. If you ever blow one of these fuses it is important that it only be replaced by the exact same type and size. These fuses can be hard to find and cost considerably more than conventional fuses so the temptation is to just stick a regular buss fuse in just to get the meter working again. If the incorrect fuse is installed you may not have any short circuit or over current protection. If you ever buy a used meter the very first thing to do is check that these fuses are of the proper size and type before ever trying to make a measurement with it.

    I can't tell from the photo of your meter but does it have a CAT rating? All test meters manufactured today have a CAT, short for Category, rating of either I, II, III or IV. This is an indication of how much internal short circuit protection is built into the design and construction of the meter itself. Or, in other words, how much short circuit current it can handle without exploding. The higher the number, the greater the amount of protection. You said in your post that you wanted to measure 220 volt circuits. The fault currents in 220 or 240 volt circuits can be much higher than conventional 120 volt circuits. For this type of use you need a minimum of a CAT III rated meter and leads. An unrated, old, meter or a CAT I meter should only be used for making measurements inside 120 volt equipment that is plugged into a wall outlet. If you want to measure three phase circuits than only a CAT IV meter should be used. If you want to see why this is important do a search on youtube for "exploding meters". Yes, a CAT III meter will cost a few dollars more than an elcheapo chinese import but not really that much more. And they can usually be found in most any big box home center store.
     

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