Why are Multimeters 10A and not 20A?

[e0ne199]

probably it has something to do with safety...anyway, who is dare enough to measure live AC or DC current with current more than 10A using probes?
especially AC current, one wrong move and you are dead...because what is the most dangerous thing about electricity is its current...

[windsmurf]

probably it has something to do with safety...anyway, who is dare enough to measure live AC or DC current with current more than 10A using probes?
especially AC current, one wrong move and you are dead...because what is the most dangerous thing about electricity is its current...

One wrong move at 100 milliamps and you're dead too, according to this:



From: https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html

I like how they indicate death between .1 and .2 Amps only, as if above that you won't die... you just stop breathing 

[windsmurf]

Thank you Fungus!  Its interesting they use 20A fuses but only tell you 30 seconds max... I wonder if the fuse will really blow at 20A?

No, it won't. A fuse rated for 20A will in theory that forever to blow at 20A, it needs more.

So I guess the 30 second limit they write about in the manual is because the shunt gets too hot or the probe leads getshot... like Fungus said, its like they took a 10A meter and just put a 20A fuse in it, just so they can claim its a 20A multimeter... so I guess none of those meter safety certifications cover this kind of thing... ?

I also thought BK Precision was supposed to be a reputable brand.

[rancor]

One wrong move at 100 milliamps and you're dead too, according to this:



From: https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html

I like how they indicate death between .1 and .2 Amps only, as if above that you won't die... you just stop breathing 

From the source you linked that seem to be true. I can't find other sources about why that is the case.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal. Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

[David Hess]

probably it has something to do with safety...anyway, who is dare enough to measure live AC or DC current with current more than 10A using probes?

I have occasionally and it is one reason I much prefer the terminal arrangement on multimeters where every terminal is equally distant from common so standard 3/4" dual banana plugs may be used.

But I do not use standard test probes.  Instead, I make a custom test lead using appropriately sized wire and a 3/4" dual banana jack and just wire the multimeter into the circuit temporarily which could be days or weeks.

[max_torque]

May i suggest an altogether less exciting reason?  Simply the fact that the need for more than 10A DC current measurement is simply unusual and hence rare.

Most people use multimeters for bench top electronics (needing a couple of amps max) to fault find appliance wiring, and to do some basic automotive investigations.  Just like most people don't have a bench top power supply rated for more than 10amps, most people simply don't need to measure more than 10 amps!  Due to resistive heating and I2R losses, most products and applications will where-ever possible, run at a higher voltage and lower current for any given power requirement!

The exception is of course passenger cars, stuck at 12v nominal, but even here, 10 A is 120watts (more like 150w when the engine is running at system voltage is 14.6v) which is a significant amount of power, and really only exceeded by big current devices like the starter motor or the alternator etc.

I think over the years i've been doing electronics, both hobby based on the bench, i've either needed less than 10A, or waaaayy more (like >100A), meaning a 20A multimeter is completely pointless...........

[BillB]

From the source you linked that seem to be true. I can't find other sources about why that is the case.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal. Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

Maybe its the smoldering, smoke and smell of burnt flesh that cause the onlooker to react more quickly and seriously thus initiating resuscitation and revival?  Below that (.1-.2A), the onlooker just kicks at the person, perhaps pokes them with a sharp stick, and ridicules them for being a wuss?   

[Fungus]

I think we should also ask why they don't measure up to 2000 Volts. Why stop at less? 

[tautech]

I think we should also ask why they don't measure up to 2000 Volts. Why stop at less? 

Exactly.....why not even 3KV ?
If you repair old CRO's this is a necessary requirement.

[David Hess]

Most people use multimeters for bench top electronics (needing a couple of amps max) to fault find appliance wiring, and to do some basic automotive investigations.  Just like most people don't have a bench top power supply rated for more than 10amps, most people simply don't need to measure more than 10 amps!  Due to resistive heating and I2R losses, most products and applications will where-ever possible, run at a higher voltage and lower current for any given power requirement!

If you have ever used a multimeter with a 2 amp range for long enough which used to be common, then you will identify another reason for the 10 amp range which operates up to 20 amps or more intermittently.

It is very easy to blow the 2 amp fuse with a nominally less than 1 amp power circuit measurement due to things like capacitve inrush currents.  I regularly use the 10 amp range even when I know I will be measuring currents within the nominal capacity of the next lower current range simply so that I do not blow out the lower current fuse.  Conveniently, 10 amp ranges usually or at least often deliver 1 milliamp resolution.

I think we should also ask why they don't measure up to 2000 Volts. Why stop at less? 

Exactly.....why not even 3KV ?
If you repair old CRO's this is a necessary requirement.

Back when CRT repair was more common, many portable meters did support up to 3000 volts so they could directly measure the cathode voltage.

[tautech]

I think we should also ask why they don't measure up to 2000 Volts. Why stop at less? 

Exactly.....why not even 3KV ?
If you repair old CRO's this is a necessary requirement.

Back when CRT repair was more common, many portable meters did support up to 3000 volts so they could directly measure the cathode voltage.

Sure for analog meters but newer DMM's 3KV capability is pretty rare.
My 1980 Kaise and mid 70's AVO 8 Mk5 both have 3KV ranges.....albeit via dedicated sockets.

[rsjsouza]

I think we should also ask why they don't measure up to 2000 Volts. Why stop at less? 

Exactly.....why not even 3KV ?
If you repair old CRO's this is a necessary requirement.

Yes... As I said before, it seems to be as arbitrary as any other choice. At least for voltage, <1kV is arbitrarily classified as "low voltage" for distribution systems.

Regarding current, the designer of the venerable Fluke 8060A already mentioned the decision process taken at the time. 'nuff said (at least for me  ).

Sure for analog meters but newer DMM's 3KV capability is pretty rare.
My 1980 Kaise and mid 70's AVO 8 Mk5 both have 3KV ranges.....albeit via dedicated sockets.

Puny digital circuits and their fancy-schmancy sensitive inputs... Our ICE 680R went to 2kV with the range doubler button and no dedicated inputs. 

[windsmurf]

From the source you linked that seem to be true. I can't find other sources about why that is the case.

While any amount of current over 10 milliamps (0.01 amp) is capable of producing painful to severe shock, currents between 100 and 200 mA (0.1 to 0.2 amp) are lethal. Currents above 200 milliamps (0.2 amp), while producing severe burns and unconsciousness, do not usually cause death if the victim is given immediate attention. Resuscitation, consisting of artificial respiration, will usually revive the victim.

Maybe its the smoldering, smoke and smell of burnt flesh that cause the onlooker to react more quickly and seriously thus initiating resuscitation and revival?  Below that (.1-.2A), the onlooker just kicks at the person, perhaps pokes them with a sharp stick, and ridicules them for being a wuss?   

 

Yes...  and check the circuit to see if the victim received more than .2 amps... if so, begin resuscitation and call the paramedics.  If they received between .1 and .2 amps, then don't bother with resuscitation attemps; don't call an ambulance; immediately call the morgue.   

[David Hess]

Back when CRT repair was more common, many portable meters did support up to 3000 volts so they could directly measure the cathode voltage.

Sure for analog meters but newer DMM's 3KV capability is pretty rare.
My 1980 Kaise and mid 70's AVO 8 Mk5 both have 3KV ranges.....albeit via dedicated sockets.

I suspect that by the time that digital multimeters became commonly available, they figured this feature was not such a good idea and could be left to safer high voltage probes or more specialize instruments.  There was also a trend to lower voltage testing in general because of the shift in technology from vacuum tubes to solid state circuits.

I have actually had this issue come up a few times since working to restore analog oscilloscopes.  It would be very handy to have a meter with 3 kilovolt capability built in but I make due with a 15 kilovolt high voltage probe.

[tautech]

Back when CRT repair was more common, many portable meters did support up to 3000 volts so they could directly measure the cathode voltage.

Sure for analog meters but newer DMM's 3KV capability is pretty rare.
My 1980 Kaise and mid 70's AVO 8 Mk5 both have 3KV ranges.....albeit via dedicated sockets.

I suspect that by the time that COMPACT digital multimeters became commonly available, they figured this feature was not such a good idea and could be left to safer high voltage probes or more specialize instruments.  There was also a trend to lower voltage testing in general because of the shift in technology from vacuum tubes to solid state circuits.

I have actually had this issue come up a few times since working to restore analog oscilloscopes.  It would be very handy to have a meter with 3 kilovolt capability built in but I make due with a 15 kilovolt high voltage probe.

Appropriate addition above ^

As we wish for more and more capability from an instrument something always suffers and where a heap of capability is squeezed into a handheld it's little surprise the KV ranges have been dropped.
The AVO's of old while not really a handheld were very portable more so than a bench meter and while new standards insist everything must have some CAT rating, the AVO's in particular were subjected to a 7KV flashover test.
Their original leads are of excellent quality but difficult to find in good condition these days.

[EEVblog]

Thank you Fungus!  Its interesting they use 20A fuses but only tell you 30 seconds max... I wonder if the fuse will really blow at 20A?

No, it won't. A fuse rated for 20A will in theory that forever to blow at 20A, it needs more.

So I guess the 30 second limit they write about in the manual is because the shunt gets too hot or the probe leads getshot... like Fungus said, its like they took a 10A meter and just put a 20A fuse in it, just so they can claim its a 20A multimeter... so I guess none of those meter safety certifications cover this kind of thing... ?

I also thought BK Precision was supposed to be a reputable brand.

Yep, a 20A fuse in a non-continuous 20A rated meter seems completely dodgy.

[shakalnokturn]

Unless you can still find some of those fuses that blow in 30 seconds at 20A...

[Electro Detective]

Unless you can still find some of those fuses that blow in 30 seconds at 20A...

Even if you find them, you won't buy them

They cost as much as a multimeter

Anything over 8 amps best to buy an AC/DC clamp meter or clamp attachment and optional CDs >>> Highway To Hell and Back In Black

The meter shunt, PCB and leads will thank you for it   

[golden_labels]

Someone has earlier mentioned wires and banana jacks as the possible cause of meters being limited to 10A.

I’ve checked, how much can some non-specialized wires handle. The burden voltage across a single wire at 5A⁽¹⁾⁽⁴⁾:
Original UT70A 116cm, needle: 441mV
Original UT70A 20cm, alligator: 338mV
Shenzhen Market 99cm, needle⁽²⁾: 640mV
DT830 66cm, ROTFL quality⁽²⁾⁽³⁾: 653mV
UniT probes are perhaps not the top quality, but decent enough and I doubt you can get extremely better for kit probes. So even with that we have nearly 1V drop. Extrapolating to 20A: it would be nearly 2V and over 15W in heat. So I guess the hypothesis, that this is a factor, makes sense: a multimeter would have to be supplied with probes designed specifically to handle 20A.

A quick check on Digikey reveals that indeed banana jacks are generally sold in the 5–15A range.

For entertainment alone I’ve checked, how Shenzhen Market alligator wires deal with current. Those which you may hunt down for $0.10/10pcs and treat as expendable. The result is in the attachment.
____
(1) I have no meter to measure 10A or a power supply good enough to provide exactly that value.
(2) Added only for completeness, because I had them around.
(3) So bad that the needles have fallen off before the first use.
(4) All measurements at 5A±3%, 60s for letting the current stabilize, 10 samples mean with ±0.5%,1d accuracy.

[ptricks]

It is a very good question. I'm guessing that economics comes into it somewhere, the ,we could do more amps but what are people most likely to need for the cost to us, mentality. 10A is a number that isn't too high and not too low, it is probably what I would have picked.

[Electro Detective]

For entertainment alone I’ve checked, how Shenzhen Market alligator wires deal with current.

Those which you may hunt down for $0.10/10pcs and treat as expendable. The result is in the attachment.

As per your picture above  Shenzhen Market alligator wires deal with current badly because OneHungTooLow either crimps the wire poorly,

or the solder does not flow on to the alligator/croc properly, hence the high resistance hot spot/BBQ 

i.e. the solder is crap, so is the wire, the alligator has an oily film on it, so has the wire,

the  'will solder for food' flip flop and shorts wearing tech is wielding a OHL soldering iron with not enough heat,

the iron is dirty and or knackered.. the list goes on and on and on... 

Cheap car jumper cables aren't much better, and give little to no love trying to pull 200 amps on a cold night to power up a flat car battery.

The rich local dirt belly importers that make their money flogging such rubbish, crap they would never use themselves, need a good public tar and feathering

and a rodgering by a gorilla well, I won't say it here 

[Berni]

Yep cheap crocodile clips are always horrible. Be careful!

The wire they use is tiny and its always crimped into the crocodile with the copper strands bent back against the insulation and shoved in with the insulation included. This sort of crimp joint is high resistance and very unreliable.

Looking around enough you can get properly made ones where the crimp only holds the insulation while the wire is soldered to the crocodile with a nice well flowed out ball of solder. One such that i have found are the SparkFun branded crocodile clips( https://www.sparkfun.com/products/12978 ). The wires handle a few amps just fine too (Despite looking so thin, most of it is copper inside).

Because of this i developed a test routine that i run my crocodile cables trough. They are put across a PSU set to 3A and then having there cables janked and wiggled while watching that the voltage drop stays constant, then the 3A is left to flow trough them for a few minutes. If they keep consistent drop and get slightly warm they pass, if not they are banned from the crocodile clip storage area.

Tho sometimes clips are decent, but just the wire is crap You can fix those by just ripping the wire out the back and properly attaching your own nice thick flexible silicone wire, worth the few minutes of work to get crocodile wires that are superior that almost anything you find in a store.

[madires]

One of my DMMs does 20A for 10s and requires a pause of 15min before the next measurement (protected by a 10A fuse). I think the main reason for a 10A range is cost vs. market value. A DMM properly designed for 20A would be larger and more expensive while not many users would need the 20A range. Why adding an expensive feature to a "mass market" product? For high current measurements I'd use a clamp meter (no burden voltage) or an external current shunt for more precision.

[joeqsmith]

Or some sort of magnetoresistive sensor.   I have a few made by LEM (the blue device mounted to the side).

[joeqsmith]

Weston 6000 from 1976 showing an intermittent 15A for 15 seconds.  Max, of 20A with the 0.01 ohm shunt.