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I have read the manual for my new multimeter but unsure which (red) terminal to use for what. The meter has one VΩmA fused 500 mA max terminal and one Unfused 10A Max terminal. I just want to measure the voltage of a wall outlet. Which terminal do I use? It would be great with some examples of what the 10A terminal is used for as opposed to the VΩmA terminal. I'm not an electrician by any means so the manual is not covering this.

Christian
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    RTFM (again). The "10A" terminal should ONLY be used when measuring amps, and only when the 10 amp range is intended. All other measurements should be made using the VΩmA terminal. – Hot Licks Feb 29 '20 at 23:53
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    @HotLicks arguably an *Unfused* 10A multimeter terminal should not be used for anything – Pete Kirkham Mar 01 '20 at 15:35
  • @PeteKirkham - Then why do they provide it if it should never be used for anything? I'm not an electrician by any means, same as OP, but I'm curious... – William Mar 01 '20 at 17:34
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    I'm not well versed in electric terms so "only used to measure amps" doesn't really tell me what I can use the terminal for. Thank you for pointing out that the manual should be sufficient for those who knows these things. I used it on my troubled outlet and got the reading I needed. – Christian Mar 01 '20 at 18:03
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    @Christian: When you measure voltage (in volts), the meter acts as a resistor -- some electricity passes through it, but it's (ideally) not a lot. By contrast, when you measure current (in amps), the meter is essentially a wire (rather than a resistor), allowing the current to flow through it at full force. Their point was that the higher-current terminal shouldn't be used unless you need the higher-current tolerance specific to that terminal. – Nat Mar 01 '20 at 21:45
  • None of them because that's the wrong tool. [Electric shock - was I stupid, unlucky, or a combination of both?](https://diy.stackexchange.com/a/47653/23295) – Mazura Mar 01 '20 at 22:38
  • @William because people who don't know better will buy it, just like you can get adapters that fit UK sockets which are not fused or properly earthed. Not everything people produce is safe, and it's almost always possible to make a cheaper version of a product by cutting corners. Many cheap multimeters also lie about their CAT status. (it turns out the device in question is fused, but there are some unfused ones < $10 on ebay, you'd have to look inside to see whether it meets its claimed CAT status) – Pete Kirkham Mar 02 '20 at 09:18
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    Adding to what @Nat said: when used as a voltmeter (to measure volts), the meter is in *parallel* to the load. When used as an ammeter (to measure amps), the meter is in *series* with the load. – Z4-tier Mar 02 '20 at 12:49
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    @Nat Thank you. I do not enjoy exposing my ignorance but rather that than being electrocuted or burning down the house. I understood it better now and will get a better meeter! – Christian Mar 02 '20 at 12:52

3 Answers3

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Stay away from the 10A terminal. That is for amp measurements ONLY, and creates a dead short between the 10A terminal and the common. This will blow your fuse, burn up your probes, and/or destroy the meter. Never use that unless/until you know exactly what you are doing.

Harper - Reinstate Monica
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    I did that when I was a kid and bored. I knew better, but I wasn't thinking. It made impressive fireworks, blew a chunk out of a probe, and the 10A scale didn't work anymore. – AaronD Feb 29 '20 at 22:27
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    @AaronD - Yep, blew out a resistor in my newly-constructed Heathkit VOM when I was about 14, from switching between volts and ohms at the wrong moment. – Hot Licks Feb 29 '20 at 23:51
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    *Stay away from* using a multimeter to check for a 'trouble outlet', full stop. They're for checking that the incoming power is what it's supposed to be, and (not that I've ever had to, but if I did) I'd RTFM again. - I use solenoid voltage detectors; no reading required, and as long as you don't keep it lit for more than ten seconds, and don't try to check voltages higher than 440 (which you literally shouldn't even go near) it *will not* blow up in your face. – Mazura Mar 01 '20 at 22:34
  • @AaronD Let be honest, we've all done this. When I was a bored kid though, I thought it would be fun to wrap a coil of enamelled wire around the three pins of a UK plug, and plug it in. (My dad was an electronics engineer, and had been showing me stuff about electromagnets). Made a *big* flash, and parents came running :) I guess I'd wrapped it tight enough to break through the enamel on a few turns. – SiHa Mar 02 '20 at 12:52
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Keep in mind that using a meter that's not rated for the task can be dangerous! Even with relatively low risk things like residential receptacles.

Right off the bat - if you got this meter for free with a purchase of a blue tarp at Horrible Freight, just throw it out.

Next, make sure the meter is properly rated for the task. Meters have CAT ratings roman numeral I through IV, and are designed for safe use depending on the application. For residential receptacles, it should be marked CAT II, and should be from a maker you trust to properly rate their products. (Hint - reputable makers don't give away meters free with a blue tarp.)

Technically, for CAT II the receptacle should be at least 30 feet away from the electrical panel supplying the receptacle; if it's right close to the panel that feeds the receptacle, you are supposed to use a CAT III rated meter.

In the comments, the original poster links their meter's web site and looking at the picture below, you see that it is rated CAT II so it's suitable for the purpose. (It also shows that the left jack, for 10A current measurements, is actually fused, not unfused as stated in the original post - which makes sense, and is a relief.)

AtroAI AM33D

So to measure voltage, yes you want the red lead plugged into the jack labelled "VΩmA" and the black lead plugged in the common jack, the configuration shown in the photo from the web site.

To address an issue that's mentioned in the comments - since safety is a factor, you don't want to skimp on a meter, and a good meter is not cheap. Plus there's a little learning curve involved using a meter correctly and safely. As an alternative, for checking voltage at receptacles, consider a Kill A Watt or similar plug in device:

Kill A Watt

This measures voltage as well as power utilization and it's dead simple to use, safer than a toaster.

batsplatsterson
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    Thank you for a educational lesson! I did buy the meter. It's a cheap one ($12). You can see it here: https://is.gd/AvPjBz The manual is available online also. I do not use a meter often so I didn't spend much on it thinking it would be able to do some basic tasks like this one in addition to battery checking etc. – Christian Feb 29 '20 at 14:40
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    Only buy good quality meters, one of mine is by Fluke, the other by Avometer... and they were a factor of 10 more than what you paid - good tools are not cheap @Christian – Solar Mike Mar 01 '20 at 06:32
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    @SolarMike why does OP need a $120 meter? – Tim Mar 01 '20 at 09:34
  • @Tim - if you buy a junky screwdriver, it might strip a screw. If you use a junky meter for low voltage hobby electronics, you might fry a circuit board. If you use a junky meter with line voltage, the stakes are much higher, it becomes a safety issue, junky meters are dangerous. – batsplatsterson Mar 01 '20 at 12:08
  • @batsplatsterson it doesn’t sound like OP is regularly doing any of those things. – Tim Mar 01 '20 at 12:29
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    @Tim We don't know what the OP was doing but since the question is on Home Improvement not Electronics, it's a fair bet that the mains supply was involved. As for doing things "regularly", you don't learn from your mistakes if the first one kills you. – alephzero Mar 01 '20 at 15:16
  • @SolarMike So even if I use it twice a year for checking outlets and batteries now and then this one isn't good? I have bought cheap tools in the past and prolonged a project to the extent I wasted much more money than I saved on the cheaper tools. – Christian Mar 01 '20 at 18:07
  • @Tim - the person that doesn't use it much has fewer chances for something to go wrong, but greater odds of making a mistake and having something go wrong. – batsplatsterson Mar 01 '20 at 18:11
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    @Christian a cheap screwdriver won't electrocute you, a cheap hammer will still put a nail in but a cheap meter may fail or the probe insulation is poor (guess why cheap is cheap...) and you get the shock... – Solar Mike Mar 01 '20 at 18:14
  • @SolarMike So it's cheap may fail and be dangerous. Makes sense. So how much do I need to pay to get something safe? – Christian Mar 01 '20 at 18:25
  • @Christian - I am going to edit with a suggestion. – batsplatsterson Mar 01 '20 at 23:13
  • @Christian: You shouldn’t use even a good DMM for testing the health of batteries. This puts no load on the battery, so it can give a misleading answer. Use a proper battery health tester for that. Amprobe makes [a reliable inexpensive tester](https://www.amprobe.com/product/bat-250/) that’s more useful for this specific purpose than even a $$$ DMM alone. It won’t do every battery type, but that’s on purpose: the proper test varies by battery type, so you either need several inexpensive purpose-made testers or one expensive all-in-one tester. – Warren Young Mar 02 '20 at 16:16
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Memory key: Because you want to measure voltage (V), use the VΩmA terminal.

(Also use that terminal for measuring resistance (Ω) and small currents (mA).)

The 10A terminal is special purpose, only for measuring very high current (up to 10 amps).

Dirk Helgemo
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