Why did my multimeters blew up? (AC voltage)

[BeBuLamar]

Replace the fuse in the meter then try to measure resistance with it and see.

That fuse is only relevant to current range. The rest is completely separate. Condition of the fuse does not affect any measurements other than current.

Yep, but I guess BeBuLamar was hinting that it would show impossible to measure resistance or continuity with the leads in 20A and COM connections, like the OP was sure he had done before.

The OP can count his blessings that nothing bad happened while measuring directly after the power companies meter on two phases. Fused at maybe 64A it will have been quite the blast. The fuse in the meter might not have helped against damage caused by the flash, but maybe the fuse contained it. Only way to know for sure is to open up the meter and see.

A simple test to see if the meter survived is to plug the leads in the proper connectors, COM and V..., The two connections on the right side of the meter and turn it on to continuity and see if it beeps when the probes touch each other.

I don't know about the OP meter but I have blown the fuse of my Fluke 87V many times by forgetting to put the test lead back to the correct jack and the meter survived. Just the fuse is gone.

[Gyro]

Confirming, as BennoG noted, that on some meters you can get volt and ohm readings with the probes in the high Ampere jack and the V-Ω jack. An Aneng 8008 will do this, but the EEVBlog-Brymen beeps an error with this configuration. OP thinks it was COM and 20A, but must be mistaken.

Yes, putting one probe in the highest current jack and the other in the V- Jack would give readings. As previously noted, the high current jack is naturally connected to COM via the fuse and shunt, this probably wouldn't be noticed apart from maybe on the lowest resistance range.

It makes no sense that the OP would do that though, short of liking to plug the probes into the jacks in the bottom corners of the meter. It still requires moving a probe to the COM jack to measure current - most likely, he did that. I think it can only be put down to lack of knowledge and failing to read the instructions.

[radiolistener]

pretty sure it was connected to com and 20A and than sparks

Mains can provide much more than 20 Amps, so this is the reason why it burned your DMM. Say thanks, that it didn't killed you.

If you want to measure voltage, you're needs to connect probes to Volts socket, not Amps socket.

[coppercone2]

the short circuit current of the mains can be as high as 2000A in the worst cases

Notice what your breakers are rated for, its KA. That is kilo ampers. The circuit breakers are like 5kA rated to give you a safe margin.

That is why you have a 30 dollar fuse in the multimeter, incase you do this inside of the electrical panel in a commercial building.

Gossen meters block the amps jack with a mechanical slider thingy, those are the best for total noobs doing electricity works (not electronics). I can't stand them in the lab though, awful, you need to be wearing a leather tool belt to make use of a gossen IMO.

[Fredderic]

Unbelievable how anyone would plug a lead into the current jack to measure volts!!!

Not unbelievable at all. First, there is the ignorant, who have not read the manual or know much about electronics or DMM's. Second, there is simple user error or absent mindedness. This mistake is so common that most of the "better quality" meters have a protection against exactly this mistake. A few have a mechanical interlock, which covers those banana plug holes when the meter dial is in a non-current measurement mode. But far more common is that the DMM turns on the beeper when a cord is jacked into an amps socket when it should not be. The first meter I bought with this feature (Dynatec 112) is now in my possession for over 30 years, and in that time it has saved a bunch of meter fuses.

In defence of "the young players"; Also worth noting that everyone who's looked in a fuse box, knows that there's two or three different amp rated fuses for different circuits, usually even more different values in a car.  Never different V's, though.  And on every product, the V's are mostly always the same, and only matters to make sure it's not somehow a product from an incompatible region, you learn it's the W's you have to be aware of, you probably know that the A's make up the W's (and those V's too, they're just there to help you convert between W's and A's), and probably that it's the W's that will overload your power board.  So knowing what the A's are at all, probably makes you smarter than average, doubly so if you actually understand and use them instead of the W's.  So you see the A's on the meter, and of course you know to use the right one!  And they did.

[joeqsmith]

the short circuit current of the mains can be as high as 2000A in the worst cases

Not according to the IEC standards.  There is a reason they rate the fault currents on safety fuses much higher.

[44kgk1lkf6u]

Buy a couple more meters and measure how many OHMS your power company has. Second thought......DON'T!!!

It should be fine.  My indecisive power company goes back and forth between -1k to 0L ohms.

[44kgk1lkf6u]

the short circuit current of the mains can be as high as 2000A in the worst cases

Not according to the IEC standards.  There is a reason they rate the fault currents on safety fuses much higher.

What number do they say it is?

[Xena E]

the short circuit current of the mains can be as high as 2000A in the worst cases

Not according to the IEC standards.  There is a reason they rate the fault currents on safety fuses much higher.

What number do they say it is?

How long is a piece of string?

Icu is the figure that is quoted on devices for safe breaking protection. Whatever the instantaneous fault current it has to be interrupted SAFELY.

Check out the local regulations, however a clue to that question is the breaking capacity rating printed on your MCB or RCD etc.,

6 - 10kA is normal for a final circuit in a domestic property in the UK. Some large MCCB are commonly available to safely interrupt 200kA.

One poster here put "in defence of the newbie". The fact is in these circumstances when things go horribly wrong because of abject arrogance and ignorance you don't have to defend the newbie because they are dead.

If people are willing to piss around with high energy circuits without even READING THE MANUAL for the test instrument they are trying to use, they are then nominating themselves for a Darwin award.

There are good "electricians" meters available that have no current range on them at all, any in service current measurements of high energy circuits, should for safety be made with non contact methods.

Remember RTFM

Regards,
Xena.

[MrAl]

I tried to measure AC VOLTAGE, 100% sure multimeter was set to AC voltage, i even have eye witness.

I tried to measure between L1 and L2 - result: spark, house elcb down, mutimeter does not measure. Hopefully fuse, it was my good meter.

So now, second meter AC voltage, unfussed between L1 and PE, same thing, spark, house main elcb down.
 
I was fault finding my installation, fault was not connecting Neutral wire to the distribution rail. I was doing measurements on the wires coming right from the electrical company  meter. Nothing after that was connected.

3 phase 230V connection.

Not sure if anyone said this yet but there are a few reasons how this could happen.

First, the meter was really set to measure AC current.  That would cause this kind of problem.
Second, the meter is set to AC voltage, but the leads are plugged into the wrong terminal holes on the meter.
Third, the leads are not meant for those meters but are a special type.
There could be other reasons too.

On some meters the terminal holes are all the same color so you have to be very careful where you plug the leads in.

[IanB]

Not sure if anyone said this yet but there are a few reasons how this could happen.

First, the meter was really set to measure AC current.  That would cause this kind of problem.
Second, the meter is set to AC voltage, but the leads are plugged into the wrong terminal holes on the meter.
Third, the leads are not meant for those meters but are a special type.
There could be other reasons too.

On some meters the terminal holes are all the same color so you have to be very careful where you plug the leads in.

OP already explained they plugged the leads into the 20 A and COM sockets on the meter, "as is normal for such measurements". The exploding meter is therefore no mystery.

[Zero999]

Unbelievable how anyone would plug a lead into the current jack to measure volts!!!

Not unbelievable at all. First, there is the ignorant, who have not read the manual or know much about electronics or DMM's. Second, there is simple user error or absent mindedness. This mistake is so common that most of the "better quality" meters have a protection against exactly this mistake. A few have a mechanical interlock, which covers those banana plug holes when the meter dial is in a non-current measurement mode. But far more common is that the DMM turns on the beeper when a cord is jacked into an amps socket when it should not be. The first meter I bought with this feature (Dynatec 112) is now in my possession for over 30 years, and in that time it has saved a bunch of meter fuses.

I confess, I've done it before. but through absent mindedness, rather than ignorance. I'm used to using a meter with a warning and the one time I didn't I blew the fuse because someone had been using it for current before and had left it plugged into the current socket. Fortunately it wasn't mains, just a current limited bench supply and no harm was done, other than an expensive fuse. I learned a lesson and am more careful now.

[BeBuLamar]

the mystery is the OP claimed that he can measure resistance using the same jacks 20A and COM.

[radiolistener]

Not according to the IEC standards.  There is a reason they rate the fault currents on safety fuses much higher.

CAT III and CAT IV is tested for source impedance 2 Ω.
For 300 V line test transient voltage is 4000 V for CAT III and 6000 V for CAT IV.

6000 V / 2 Ω = 3000 Amps for transient pulse.

Working current for CAT III and CAT IV is 300 V / 2 Ω = 150 Amps (45 kW).

This is for high current load socket like kitchen electric stove which is usually rated for 10 kW power.


But usual home wall outlet is CAT II, which is tested for source impedance 12 Ω.
For 300 V line test transient voltage is 2500 V for CAT II.

2500 V / 12 Ω = 208 Amps for transient pulse.

Working current for CAT II is 300 V / 12 Ω = 25 Amps (7.5 kW).

[joeqsmith]

the short circuit current of the mains can be as high as 2000A in the worst cases

Not according to the IEC standards.  There is a reason they rate the fault currents on safety fuses much higher.

What number do they say it is?

61010-2-033:2012 shows for category IV, the typical short circuit current >> 50kA. 

The short-circuit current is calculated for a 1 000 V line-to-neutral voltage and the
minimum loop impedance. The values of loop impedances (installation impedances) do
not take into account the resistance of the probe assemblies and impedances internal
to the measuring equipment. These short-circuit currents vary, depending on the
characteristics of the installation.

[joeqsmith]

Last time fault current came up, I took the time to measure a few of my home outlets for one of the members here.  Sadly, they were not able to measure theirs so we only have a few data points. 

https://www.eevblog.com/forum/testgear/trashy-meters-redux/msg4835948/#msg4835948

[joeqsmith]

Leads in wrong position
https://youtu.be/IzwN8yibjjA?t=848

Other dumb mistakes like reading the resistance of live mains...
https://youtu.be/IzwN8yibjjA?t=1135

While they run the surge test and talk about the what ifs of an arc flash event if something were to flash over, they never show any testing.   The following was taken from an article on arc flash testing that describes the setup.

An arc flash is a short circuit where the current arcs across an air gap. To conduct an arc flash test, an electrical source capable of producing thousands of amperes (A) of short-circuit current is needed. The magnitude of current can reach upward of 100,000A, depending on the test requirements.


Creating a short circuit for the test is not as simple as connecting a couple of conductors together on the lab’s electric power system. Like any other facility, the lab also receives its power from the local electric utility. If a short circuit were created using the utility as the source, serious problems could result. A short circuit causes the voltage to collapse near the point of the fault, resulting in dimmed lights and other potentially serious disturbances. To make matters worse, there is a real possibility of tripping a utility protective device, which could create a large power outage affecting others in the area. I would not want to explain to the neighbors why their power just went out.


To avoid these types of problems, most high power labs have their own generators that are used to produce short-circuit current. This gives them the capability to perform arc flash and short-circuit testing and have the test circuit completely isolated from the electric utility. The Mersen lab has two generators. Each generator is rated 10 megavolt-amperes (MVA) continuous with a short-circuit rating of 68 MVA and is powered by a 4,160-volt (V), 536-horsepower electric motor that is directly connected to the utility. When a test is conducted, the short-circuit current comes from the generator and not the electric utility.


This lab has the capability to produce up to 100,000A of short-circuit current at 480V. However, most testing requires the magnitude of current to be much less. To reduce the available current to a lower level, resistance and inductance is inserted between the generators and the test cell. The lab uses a large bank of switches to configure the test circuit with a specific amount of resistance and reactance. The exact amount that needs to be added to the circuit will depend on the specific magnitude of current required for the test.


https://www.ecmag.com/magazine/articles/article-detail/safety-lets-blow-it-arc-flash-testing

[alm]

CAT III and CAT IV is tested for source impedance 2 Ω.
For 300 V line test transient voltage is 4000 V for CAT III and 6000 V for CAT IV.

6000 V / 2 Ω = 3000 Amps for transient pulse.

This is the source impedance for the transient test which will also include inductance. Is there a specification for source impedance at mains frequency?

[coppercone2]

well i hope they don't let this guy near the IV before a few classes  '

But in the house it should be around the 2000 mark I think. And less in a distant outlet, I think I ran the numbers to what it should be in the garage and it was slightly lower because of the inductance and resistance of the wire.

I think its like 3% impedance in north america for the transformer infront of your house.

[joeqsmith]

well i hope they don't let this guy near the IV before a few classes  '

But in the house it should be around the 2000 mark I think. And less in a distant outlet, I think I ran the numbers to what it should be in the garage and it was slightly lower because of the inductance and resistance of the wire.

I think its like 3% impedance in north america for the transformer infront of your house.

Assuming we are talking about the typical 110V outlets in the USA, none of mine are even close to 2kA.  The ones I measured were all under 500A.  Consider that one outlet I checked was very close to the distribution panel.  The problem is, it's only one data point.  Maybe there are cases where a standard 110 outlet in the USA would be higher.  Maybe my meter has 100% error. 

[CaptDon]

The O.P. also stated "In the 20A Normal Jack"!!! For 99% of technicians and 99% of their tests the '20A' jack IS NOT the 'normal' jack!!

[schmitt trigger]

I am pretty sure that by now, the OP has learned the lesson.

As others have mentioned, damaging a multimeter by applying the AC mains to an incorrect range, is a common newbie mistake.

It was worse with analog meters, with its rotary selector. I myself as a curious youngster damaged a Radio Shack analog meter, attempting to measure AC volts while in the resistance range. Not only several components burned, but the meter’s needle pegged with such force that it was completely bent.

My relative was upset but not completely surprised. That is the reason he loaned me the inexpensive Radio Shack but wouldn’t allow me to touch his expensive Simpson 260.

[themadhippy]

Consider that one outlet I checked was very close to the distribution panel.

For prospective fault current the distance to your fuseboard dont really matter,its how far the supply transformer  is that makes the difference.

[bdunham7]

For prospective fault current the distance to your fuseboard dont really matter,its how far the supply transformer  is that makes the difference.

That may be true in the UK, but things are different in the US.  Transformers are often quite close and the fault currents at the panel can be many thousands of amps, but 50 feet of 14-2 wiring and 120V will limit the fault current to under 500A.

[BeBuLamar]

Well the OP use the 20A jack to measure voltage so the fuse blown. That's no mystery but the OP said he can measure resistance with the 20A jack I wonder how? I don't know about the OP's meter but I have blown fuse on the Fluke meters 87V and 287 by doing exactly what the OP did and only the fuse was blown and some damage to the test probe but the meters were fine.