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Most multimeters have a current measurement setting for low currents where a fuse is present. However, to measure high currents up to 10A, you need to use a second input that is often unfused.

Now, I understand why a second input is needed (the low-current fuse can't support 10A currents, and you definitely don't want a 10A fuse for low-current measurements). But what I do not understand is why the 10A input may not have a second fuse that is either 10A or slightly larger than that.

So, what is the reason for the 10A input often being unfused?

I understand that some high-end multimeters may have a 10A fuse, so is this a cost related issue?

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    \$\begingroup\$ "Often unfused"? Is it really more common than I think? I've used many meters priced $500+ down to $6. Only on the $6 meter have I seen a non-fused 10A input (That meter was not mine). I would never knowingly buy one that didn't have fused inputs. I have blown a couple 10A fuses, and I'm glad they were there. \$\endgroup\$
    – Bort
    Jul 8, 2017 at 14:35
  • \$\begingroup\$ When the inspector handed my electrical licence to me he said,"This is an electrical license not a burn permit. Use it as the former and you can earn a good living. Use it as the latter and I will send you to prison ! When doing electrical work--ALWAYS BE SURE--if you're not sure--FIND OUT ! \$\endgroup\$
    – TAMMY
    Jan 4, 2021 at 5:28
  • \$\begingroup\$ @Bort I have seen inside a large number of cheaper meters over many decades*. Almost all had no 10A fuse. These were typically in the sub $50 range and some sub $200. (* Almost 6 :-) ) \$\endgroup\$
    – Russell McMahon ♦
    Jan 4, 2021 at 11:28

2 Answers 2

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10A won't go through the switch, so you need a separate input. Once it's separate, few people measure car batteries, and they're the only people likely to blow a 10A measuring shunt.

A fuse holder is cost, size and inconvenience, so it's only provided on the more expensive professional meters.

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    \$\begingroup\$ Not only that but a fuse will increase the burden of the meter - the voltage drop across the fuse could be significant. Typically the shunt for the high-current range is just a length of exposed heavy gauge wire so there is not much to protect. The rest of the meter is protected even in the event of overcurrent. \$\endgroup\$
    – Kevin White
    Jul 8, 2017 at 17:40
  • \$\begingroup\$ "... few people measure car batteries, and they're the only people likely to blow a 10A measuring shunt." - What about mains current measurements? \$\endgroup\$
    – marcelm
    Jan 4, 2021 at 11:51
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If you inadvertently connect your multimeter to a circuit that can blow a 10 amp fuse you know about it before the display has a chance to flicker onto an out-of-range value. So in an un-fused meter, a large current flows and you get some kind of crack sound and maybe a puff of smoke that tells you your cheap meter is now broken and that you have to buy a new one.

There will be undisputable evidence inside the meter that you have misued this meter so trying to take it back to the shop to get your money back is off course not going to work. So you throw it away and learn from your mistake.

Cheap meters are, of course, really cheap and, the cost of a replacement is a cost worth paying for the valuable learning experience that most of us have done once and never (touch wood) repeated.

I understand that some high-end multimeters may have a 10A fuse, so is this a cost related issue?

Yes.

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    \$\begingroup\$ Right. A cheap 10A multimeter is a fuse that doesn't meet CATIII standards. I wondered why a thin-wire link in such a meter (that looked fuse-like) had insulation on it. When tested, the insulation produced volumes of white smoke - a useful visual indicator! \$\endgroup\$
    – glen_geek
    Jul 8, 2017 at 13:44
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    \$\begingroup\$ Sort of like the testimony by a car-maker many years ago who denied that catalytic converters could catch fire without warning. He pointed out the the converter will glow cherry read for 30 seconds first. \$\endgroup\$
    – WhatRoughBeast
    Jul 8, 2017 at 14:04
  • \$\begingroup\$ As an amateur in electricals who just connected the 10 A unfused to the terminals of a 400v 470uF capacitor I can second that you want to be careful. The multimeter is surprisingly fine but the terminals are charred and so is the capacitor... About 10 mins earlier to this this I realised the cap was charged and that I should discharge it as I felt the surge through my finger tips when I accidentally brushed over the terminals... Luckily I wasn't grounded as I wasn't touching anything else... Lesson: Respect capacitors and high amperage circuitry... \$\endgroup\$
    – NotoriousPyro
    May 18, 2020 at 17:44

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