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simulate this circuit – Schematic created using CircuitLab


A DT-830B meter.

I bought a new transformer, and I was trying to measure the output voltage. I plugged the probes on 'VΩmA' (not 10 A) and COM. and set it to 750(not 100% sure if i put it on 750 or 200) ACV.

Then I put my probe on the right side of the picture, which is the transformer output, and I got no numbers reading.

Then I wanted to check if the outlet was working right, and put the probe like the picture. My outlet has only two outputs, with no neutral/hot labeling, just two of them and they are 60 Hz 220 VAC.

Anyway, as I put the probes like the picture, the multimeter made zipping noises and it didn't display numbers. Maybe it was shorted inside? I put it like the picture again, and the fuse exploded.

Did I do anything wrong? I didn't think that I needed to swap to 10A because (I thought) it's only used when measuring currents. I just wanted to measure voltages.

Can you tell me what i did wrong?

  • oh, and I actually did put the probe on voltage measurement terminal.. It says VΩmA. I put my probe on VΩmA and COM.

Also I dont remember where I bought it, but the multimeter says DT-830B, and no make printed.

Plus, I think it was under 10 dollars.

Well, some of you wanted the inside of that meter. So I'm uploading some of the pictures. The inside looked simpler than I expected...

asdf asdf asdf as dd

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So you set it to amps measurement to measure voltages? – PlasmaHH Feb 23 at 13:01
If you aren't exactly sure of what you are doing, you shouldn't mess around with circuits connected directly to the 220VAC outlet. You might end up getting injured or even killed. – Peter Karlsen Feb 23 at 15:18
What jacks are available for you to plug your multimeter probes into? – Frank Feb 23 at 15:55
@DirkBruere People died from using a consumer multimeter on house wiring 110V/220V? Assuming they weren't in a full bathtub at the time or something ridiculously dangerous, do you have any references / warning stories I can read? – Xen2050 Feb 23 at 19:02
While jumping to the conclusion that you'd connected in the wrong mode may be founded in considerable experience of people (some a lot less noob than they'd care to admit) doing just that, it does not appear to have been an accurate jump for those that took it here today. – Ecnerwal Feb 24 at 4:17

10 Answers 10

Ok, let's first get some things out of the way that may have to do with misapplication of a multimeter...

Depending on the exact type of multimeter you use, your mileage may vary, but here's my guess about what happened, assuming your multimeter has separate inputs for current and voltage measurements, often labeled "[mA] [A] [COM] [V,Ω]" or something along that line...

No matter how you set the dial, if you don't connect the leads to the "Volts" input (and to any of the "Amps" inputs instead), you connect your multimeter's internal current sense resistor (shunt) across your transformer's output. This means, in basic words, you are creating a near-short across your transformer, and any (usually large!) current your transformer is able to deliver will rush through your poor multimeter.

Hmmm... considering your edits/clarifications... The multimeter should not become damaged if you connect the probes to "COM" and "V-Ohm-mA" and put the dial to any of the "Volts" positions. With any other setting (Ohm, Amps), you put the multimeter's current sense resistor (shunt) across your transformer's output (bad!), or the current source that your multimeter uses to test resistors will try to drive against the transformer's output (and it will find out that there's no way to win in this fatally hopeless situation).

Since you mention (in a later edit) that you can pretty much rule out any of these issues, there is of course a (somewhat rare & remote) possibility of a fault within the multimeter, and we're looking at this now...

The layout of the traces, and of any wires and components inside the multimeter must of course be designed to withstand the voltages they are exposed to during normal operation and allow for some safety margin. The pictures you edited into your question look like your multimeter may actually have contained a small spark gap because of horrible manufacturing skills - one gets what one pays for...

Here's a picture of a spark gap you can buy if you need controlled breakdown properties:

Spark Gap (Source: Wikipedia)

Here's a picture of a possible spark gap that no one actually wants ;-)


It appears that the three wires used to connect the main board and the banana socket board are (i) soldered with horrible quality and, more importantly, (ii) should have been clipped before the assembly was put into the enclosure. I guess the two top wires may have become bent while the instrument was put together and were really close to each other. Once you applied your transformer's voltage to the terminals, you probably ended up causing sparks between the wires. Note how the [10A] jack is connected to the [COM] jack by the shunt resistor (the big thing that looks like a U-shaped wire), so the middle wire can cause arcing to any of the two outer wires. By the looks of it, you had sparks between the top and middle wires, because there are little balls left from the arc's heat (sorry, i can't find an English word for Schmelzperle, maybe someone can edit).

So, yes, there is a possible piece of evidence that you used your multimeter the right way and you actually observed a fault caused by bad manufacturing.

What to do now?

Given you are a trained electrician (disclaimer, disclaimer ;-), you could clip the wires, fix the bad soldering, re-assemble the multimeter and chances are it will still work, maybe even better than ever before ;-)

It might be a very good idea, though, to limit the use of your repaired multimeter (or any similar model) to safe, low-voltage measurements, because it's worth considering...

Some notes about safety

Just like there's a direct, low-resistance path between [COM] and [10A], there is also a connection between the transistor socket and the three inputs on the bottom right. You can download a report with impressive pictures and a short video from the website of a German authority. The text is German, but the pictures tell the story pretty well. Since it's a publicly available report issued by a government agency, I have taken the freedom to copy two pictures.

One shows a very bad idea - do not attempt to try this at any time, neither at home nor somewhere else: DMM and transistor, safety hazard

Another one shows an explosion probably caused by a cheap fuse not capable of breaking large currents. Note the giant transformer in the background, such impressive "boom" can usually not be achieved on a domestic outlet. However, if you subject a multimeter to DC (as when testing, say, a computer's switching power supply), arcs will sustain (because the current has no zero crossing like in AC). Note how your multimeter developed an internal spark even though you used it correctly, because it lacked the proper clearance and creepage distances. With DC, the spark might turn into an arc and indeed cause a fire, maybe even right in your hand holding the meter. DMM safety hazard

Again, pictures taken from Hessisches Ministerium für Soziales und Integration

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But OP did connect it to the voltage terminal. He says "I plugged the probes on 'VΩmA' (not 10 A) and COM" ... "oh, and I actually did put the probe on voltage measurement terminal.. It says VΩmA. I put my probe on VΩmA and COM." – abligh Feb 24 at 9:36
@abligh you're late to this question. Originally it said he connected it to the 250mA jack (not 10A). Look through the edits on the original post before criticizing answers. – derstrom8 Feb 24 at 13:15
@abligh I edited my answer as new information became available by the OP (he edited more info into the question). – zebonaut Feb 25 at 10:28
@sjsh Your profile says you are a high school student (so not a trained electrician or engineer - yet?), so here's my advice: Maybe you have a friend/teacher trained professionally to work on electrical devices and you can have her or him help you re-solder and clip the wires and re-assemble the meter. Chances are it'll still work. Buying a new meter? Pay a bit more for a better model and hope to get better quality. Your particular no-name model is assembled and soldered in a really bad way and we can only guess it was made at the worst possible sweat-shop under horrible working conditions... – zebonaut Feb 25 at 10:50
FWIW, there's no direct translation of Schmelzperle in English, but I certainly have a new favourite German word. In this case, though, I would use the term "deposits" to describe the blobs. – Polynomial Mar 17 at 14:21

When measuring voltage your probes must be connected to the jack labeled "ACV" and to COM. The Multimeter must be set to "ACV" as well. When you connected one of the probes to the 250mA jack and measured across 220V you put 220V directly across the shunt resistor used for measuring current. Here's a simple diagram of how the multimeter measures current:

enter image description here

The probes are represented by the "dots" at the top and bottom of the image.

A multimeter actually can't measure current exactly. Instead it measures the voltage across a known resistance (the shunt resistor) and calculates the current using Ohm's Law. Generally the 250mA measurement has a shunt resistor value of approximately 1 ohm (though it will vary depending on which meter you have). Let's assume it is 1 ohm though. You connected 220V directly across it, which means that based on Ohm's Law, 220V/1R = 220A tried to flow through it. At that current the shunt would need to dissipate 48.4kW (\$I^2 \times R\$, or \$V \times R\$). That's not happening, and it would have melted long before that. When measuring voltage, ALWAYS make sure your probes are connected to the voltage measurement jack. Also, when you measure current, make sure to put your meter IN SERIES with the load, not across it.

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This doesn't apply to the DVM he used. It has no "voltage measurement jack," instead a V-OHM-mA jack. – wbeaty Feb 24 at 6:11
Obviously nomenclature varies from meter to meter but it should still be clear that he needs to use the jack with the "Volts" label (V) – derstrom8 Feb 24 at 13:13
Thanks @Ricardo for the edits. The formulas look much better now! – derstrom8 Feb 24 at 13:18
My pleasure. Formatting formulas using MathJaX (LaTeX format) is sometimes easy and have a large impact on presentation. I edit a formula here and there whenever I can... it became a hobby. – Ricardo Feb 24 at 13:46
> clear that he needs to use the jack with the "Volts" label. @derstrom8 There is no such jack. Again, it doesn't apply to the DVM he used. His proper jack has a volts/amps label, not a volts label. If his selector knob isn't set exactly on "200 V," the test probes could connect internally to the microamps shunt. 200V is next to 200uA on the selector. Very bad design – wbeaty Feb 25 at 8:16


simulate this circuit – Schematic created using CircuitLab

Figure 1 shows what you did. You connected a milli-ammeter (250 mA) across the mains. It probably has a resistance of about 1 Ω which, by Ohm's Law, would cause a current of \$ \frac {V}{R} = \frac {220}{1} = 220 A\$ to flow very briefly before the fuse blew. Meanwhile the digital electronics which was expecting to see about 250 mV across the 1 Ω resistance (the shunt) would have seen almost mains voltage. This almost certainly damaged the electronics unless it is a high quality meter with excellent protection.

Figure 2 shows what you should have done. i.e., Switch the meter to volts and use the V and COM sockets.


simulate this circuit

Figures 3 and 4 show a hypothetical multimeter circuit. The meter is full scale when 250 mV is placed across its terminals.

  • To use it as a 250 mA ammeter we use a 1 Ω shunt resistor, measure the voltage drop across the resistor when current is flowing through it and read that off as mA. Placing 1 Ω across the mains causes a very high current to flow.
  • To use it as a 250 V meter we need to divide the voltage by 1000:1. This we can do with a pair of resistors. In this case I have chosen the pair to give 1 MΩ total resistance - similar to many digital meters. At 250 V across the probes the voltage is divided down to 250 mV across the meter.

Figure 3 circuit will blow the meter. Figure 4 circuit will work and survive.

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Thank you very much for detailed answer! – sjsh Feb 24 at 3:27
But the OP appears to have done exactly what you recommend. It's set to Volts in the picture and per his text, and says "I plugged the probes on 'VΩmA' (not 10 A) and COM" ... "oh, and I actually did put the probe on voltage measurement terminal.. It says VΩmA. I put my probe on VΩmA and COM." – abligh Feb 24 at 9:37
@abligh: The story has changed. (See the revision history and the comments in the OP.) He originally said he set the meter to 250 mA. Who knows? – transistor Feb 24 at 14:55
See the revision history, indeed. He mentioned the jack as 250mA (but did not specify that it was of the shared mA-V-Ω type initially), and he also mentioned, right there in version 1, ACV measurement. He NEVER said he was set to measure current. – Ecnerwal Feb 24 at 20:00
@Ecnerwal: "I was trying to measure the output voltage. so i plugged the probes on 250mA(not 10A) and COM. and set it to 250ACV", and a hand-drawing in pixel-paint was all I had to go on. There was no picture of the meter at the time and most have one or two dedicated sockets for current measurement. His is selected by rotary switch. Any idea what smoked his meter? – transistor Feb 24 at 23:35

If your meter is of the type where 250 mA and Volts/Ohms are the same jack (you hadn't said that, but you had implied that in your description, and I, at least, am familiar with that sort of set up), it's just a junky meter that couldn't take 220 Volts, assuming you did, in fact, have it already set to measure AC Volts on a range suitable for 220VAC when you connected it.

Some "inexpensive" meters are also "cheap" in the low-quality, not actually suitable for the task, sense. You may want to shop a bit more carefully for your next meter.

Editing: Now that you have said that, and the model number and lack of make of the meter (which amazon sells for something like $6.30, with ebay probably going lower) would appear to confirm that you did have it correctly connected to measure voltage, and it was, indeed, just cheap (which is not actually inexpensive, if you have to buy one that works after the cheap thing dies.)

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Yes, my terminal says 'VΩmA', so i connected to it. maybe the multimeter was a junk. – sjsh Feb 24 at 3:28
Yes! that is exactly the one i have. thank you for editting! maybe that is generic. – sjsh Feb 24 at 4:02
The large selector-switch on your meter, does it feel very rigid? Or, is it slightly "bendy," so the internal switch parts may not point to the same position as the large knob? If the switch isn't set exactly to 200 ACV, then it can internally touch the DCA 200u setting. In that case the 200uA meter (a short circuit) was connected across 220VAC, even though the switch was approximately set to 200V setting. (This is a very bad meter design. Proper meters would have an "OFF" position between the ACV and the microamperes DC, which prevents just this explosion.) – wbeaty Feb 24 at 6:20
This would appear to be the correct answer, as despite everyone else saying OP should have connected the meter differently, at least according to what OP wrote, he was in fact using the correct jack sockets. – abligh Feb 24 at 9:38
@abligh the original post said he plugged it into the 250mA jack. – derstrom8 Feb 24 at 13:16

The existing answers do a good job of explaining why you shouldn't try to measure voltage with the test leads plugged into the current (amps) jacks on meters with dedicated jacks for current measurement -- the current shunt is a nigh-short, hence the presence of a fuse to protect it from blithering idiot moments (they're relatively common).

However, they do not explain the other half of what happened, which is the noises and damage. Cheap meters (anything under 50USD retail, basically, but especially the sub-25USD category) use ordinary glass 5x20mm or 6.3x32mm (3AG) fuses. These fuses are only rated to break surge currents up to a few dozen or perhaps a hundred amperes at 250VAC, and a mains outlet can supply several hundred amperes or more until the house fuse blows or the breaker trips. The result is that the under-rated fuse's element explodes violently instead of melting quietly, destroying the fuse, and perhaps allowing other parts of the meter to be destroyed as well.

Better meters (north of 75 USD typically, with an authentic listing from UL, CSA, TUV, or Intertek ETL) will have ceramic-bodied fuses capable of breaking kiloamperes at well upwards of 250VAC. These fuses often use a sand filler that is turned into an insulating glass around where the element initially breaks and arcs, snuffing out the arc before it can consume the entire element violently. They also have other design features, such as internal plastic shields and slots in the circuit board, that keep arcs from bypassing the fuse, or any failures of the fuse from damaging other parts of the meter.

BTW: considering your meter is one of those cheapies that multiplexes voltage and current probing onto the same jack, using the range switch to select between the multipliers and the mA shunts -- any number of things could have happened, not just an exploding fuse. ('Tis why you don't see that design on a Fluke.) Cheap meters not only cheap out on the fuses, they omit other input protection components used to keep overvoltages from damaging sensitive meter bits (there are high-voltage resistors, surge-clamping varistors and diodes, and PTCs that heat up to shut off excess current flow to protect the voltage and resistance functions on a proper meter), and do not provide sufficient clearance and width for tracks that carry high voltages and/or currents, leading to internal arcing.

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One problem with buying a meter like this is that ... there's no brand behind it, no proper datasheet, etc.. That's really bad because you have zero guarantees towards its safety and ability to meet its "specifications". In fact, this "model" seems to appear under half a dozen different brand names and occasionally no brand name at all. You want to know who designed and manufactured your meter, or at least who's getting it certified.

There's a manual available for what seems to be a very similar model. You'll note that it states:

CAT I-Measurement Category I is for measurements performed on circuits not directly connected to mains. ( Examples are measurements on circuits not derived from mains, and specially protected (internal) MAINS-derived circuits. In the latter case, the transient stresses are variable; for that reason, its necessary that the transient-withstand -capability of equipment is made known to the user.). Don’t use the equipment for measurement within Measurement Categories II,III and IV.

This multimeter (which may or may not be the same as yours despite the same "model" number) is only rated for non-mains use and is not designed to cope with high transients (brief voltage spikes), nor with low-impedance supplies! Depending on your supply quality and your local environment, transients in the kilovolt range can happen dozens of times a year.

Now, at this point it's pure speculation whether your multimeter was blown up by a coincidentally well-timed transient or due to another fault, but the fact remains that you should not use a multimeter outside of what they are rated for anyway.

Others have mentioned getting a better multimeter. It'll probably do you good to read up on meter category ratings and safety first - it's not a particularly long document, and it's fairly easy to read.

Do note that rating markings do not necessarily mean anything - anyone can print a couple bits of text. Also, CE markings are similarly self-tested (ha...). If it's been externally tested by a reputable group, e.g. UL listed, then you can usually find the certification from the certifier (don't just trust stickers/printing on the meter) so you know it's properly tested.

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It's worth reading this page from the EU safety body and comparing the image to the one here.. – David Feb 25 at 14:54
@David Hmmm... Just out of habit, I would never leave a transistor in the socket whenever I connect the multimeter to a potentially dangerous voltage because I would assume that anything inside the multimeter is connected. However, the safety warning is right, of course - and I find it kind of funny there is no fuse at all in sjsh's multimeter. Also, when comparing various pictures of DT-830x and (so-called) "DT-830x" series multimeters, I get the feeling that many are ill-assembled knock-offs of rip-offs of fakes of look-alikes of what never was a good device in the first place ;-) – zebonaut Feb 26 at 8:52
@David thanks for pointing out the document. There's even a video and a report about various multimeters. I have added some info and the links to my answer. – zebonaut Feb 26 at 9:44

The problem appears to be with your DMM.

On a multimeter with separate terminals for ammeter and other functions, the ammeter terminal is connected to the common terminal via a low-impedance path, while the other terminal is connected to a higher-impedance path. From your question, you did plug into the high-impedance terminal, which suggests that the meter was unable to cope with the 220VAC input.

If the probe was connected to the low-impedance ammeter terminal, there probably would have been a massive spark at the probes when you connected them and the whole meter (not just the fuse!) would likely have caught fire or exploded, because there would be only milliohms of impedance and you'd have thousands or tens of thousands of amps going through the meter. There's no way a small fuse of the sort used in DMMs could absorb and cut off that kind of current. Given that this was not the case, the meter was probably faulty. The ammeter is intended to be connected in series with the device under test, not in parallel as you would a voltmeter. Never use the ammeter on a low-impedance power source!

In the future, it would be a good idea to invest in a high-quality multimeter from the likes of Extech, Fluke, or Keysight (formerly Agilent)—you may need to spend upwards of $100 for a good one, although Extech has some solid ones for a bit less. Cheap DMMs can fail under high voltages in dangerous ways. I managed to blow the micro/milliammeter function on my Craftsman DMM by hooking it up to a 330VDC source (photoflash capacitor), even though the meter was specified for up to 500V above earth ground! (Thankfully, there was no explosion or fire or even any noise when that happened.)

I just noticed your edit and it definitely looks like there's no fuse holder where one should be. There are large copper pads on the PCB that have nothing on them and are simply shorted. This is quite clearly a safety hazard, and I would not use this sort of meter for anything higher than 24V, if even that.

Even my cheap Craftsman DMM has two fuses: one for the low-amperage volt/ohm/capacitance/milli/microammeter measurements, another for 10A ammeter. That meter has seen several high-voltage measurements and, save for the milli/microammeter failure described above, has been working safely for the last five years. Even a store brand like Craftsman has a major company behind it (Sears) and that provides a minimum level of assurance that the meter meets certain safety standards. I wouldn't trust it for professional work, but at least I know it won't blow up on me in day-to-day use (mainly as a battery tester). I also have a cheap pocket meter from Craftsman, and while that unit is noticeably less accurate (it seems to read a bit high), it too has a fuse. Both meters have safety certifications on the packaging: UL for the larger meter and ETL for the smaller meter; both are rated to CAT II, at 600V for the former and 300V for the latter.

Do yourself a favor and get a decent meter from a well-known brand. Extech would be a good place to start—they have some good meters that aren't too expensive. Make double-sure it has safety certification marks (and be sure to check if they're real), that it is fused, and if it has a 10A or similarly rated ammeter, that it has a separate high-amperage fuse for it.

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There are a couple other reputable DMM brands on the market -- Gossen Metrawatt and Brymen also make DMMs that actually survive the listing tests. (The Brymen models often are rebranded for local markets, as well -- some of the Extech, Amprobe, and Greenlee DMMs are Brymen rebrands, although some of the in-house Amprobe/Meterman designs are good as well.) The presence of an authentic UL/CSA/ETL/TUV listing is the best sign that your meter is going to keep you safe from harm. – ThreePhaseEel Feb 24 at 4:08
oh, i think you're right, maybe the multimeter was the problem. actually i think it's under 10 dollars. – sjsh Feb 24 at 4:09

I believe the explanation is quite simple. Although most of the answers here cover (very well) all the aspects involving this kind of measurement, a point was missed.

That kind of multimeter does NOT have a 250 ACV scale.

Actually, if you take a close look at the picture, there is no 250 scale in any unit. These multimeters are based on the ICL 7101, which has a 3 & 1/2 digit display driver, so the highest number it can display is 199.9 .

If you had set it to 750 ACV, there would be a chance for survival. Always use a scale higher than what you expect to read.

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In the briefly extant duplicate post, 750 was the scale mentioned; also the most likely of available number typos given the other scale choices. – Ecnerwal Feb 24 at 5:24

I've got also a DT-830B, but mine is different. It is also for CAT II measurements and it has a lead fuse inside:

DT-830b front

DT830b open

I can't see a lead fuse in your DT-830b and share Bobs opinion/answer.

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Is it just me, or does that fuse not look dangerously close to the 9V cell? In fact, the 9V looks like it's suffered damage as a result of incidental contact and is bulging and in danger of bursting. I wouldn't trust this DMM any further than I could throw it... – J... Feb 25 at 11:24
One thing I mentioned in my answer that I think you should also take note of is the first paragraph. Despite the rating claims on your meter, it's still lacking the backing of a known brand (i.e. knowing who manufactured it). Basically, the problem is it's pretty easy for a factory to print markings on the case without actually making sure the device satisfies those ratings. There are, of course, other ways to verify - third-party certifications like a UL listing. – Bob Feb 25 at 13:08
@J... There is a isolation between the fuse and the 9V cell (the thin grey line). – rageye Feb 25 at 18:41
@rageye Yeah, I see it now... had to stare at it for a minute. Still seems a bit scary, that little piece of paper 0_o – J... Feb 25 at 18:46
@Bob and J... : You are right, this DMM isn't save. In Germany it has been rated as a dangerous product because at 1270 V applied to the sockets there is a flashover. For isolation it must withstand at least 2210 V AC. Source: [baua.de/de/Publikationen/Fachbeitraege/… See page 62 (it's in German). – rageye Feb 25 at 22:33

I believe the OP's edits posted while I authored my original response, but for the future, remember that your DT-830B meter has inputs and settings that specifically say "10ADC" and the range dial says "DCA". Your meter can only measure DC Current.

In any event, it may not be dead. Even cheap meters have overcurrent protection fuses, and that may be all that's wrong. (Last summer I bought some true cheapies from a street vendor in Serei Saophoan, Cambodia for a class I taught at Bantey Meanchey University)

PLEASE, do yourself a favor and read SparkFun's article about how to use a multimeter.

Finally, please read my warning to @Xen2050 about 220VAC safety.

Finally, a note about 220V safety.

The USA uses 110V because it's safer than 220v-240v the rest of the world uses. It only takes 100mA to stop your heart and kill you, and 220v is plenty to overcome the resistance of your dry skin. If the current travels through your opposite arms (and thus, right across your heart, you can be killed. Here's a reference you asked for.)

I got a surprise 220v shock through the hand because I was testing one of these cheap chinese meters in the street market in Cambodia--with its back cover off. ($4 US, made in china, nice big analog meter!)

I didn't realize the probe tips were exposed on the backside. I tested it by plugging the test leads into an available outlet with one hand, while holding the meter in my other. Now Cambodia's hot in June, it was over 100F most days, and my hands were sweaty. Nice and conductive, far less resistance than normal American dry skin.

Even though I got shocked in one hand only (2" longitudinal gap across my thumb muscle, abductor pollicis brevis), it not only scared the willies out of me, my left elbow spasmodically tweaked and then hurt really bad for about three weeks.

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Your reading comprehension skills could use an upgrade, especially since you came along after most of the misinterpretable parts (due to the shared jack) had already been sorted out. – Ecnerwal Feb 24 at 4:47
"The USA uses 110V because it's safer" - somehow I doubt that's the reason. – immibis Feb 25 at 1:46
USA/north american houses have 110V and 220V, commercial buildings can have 3 phase & higher voltages & other "exotic to a regular home handyman" stuff – Xen2050 Feb 25 at 18:26

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