Potentially Dangerous Multimeter... what do you think?

[Fiveohfour]

1. Is it this a common design, to have the Voltage input shared with the amps input (mA, uA in this case).  I'd imagine you'd easily blow the 400mA fuse if you're measuring voltage and change the dial to the A.

I have looked at several meters where they share inputs like yours.  The worst ones will fuse all of the other functions with the current.  So you have your meter in the mA and blow a fuse, the entire meter is dead.  Not as common but I run into them.   I've looked at a lot of low end meters and use one still for my garage work.   I wouldn't use one in CAT III even though many claim they are fine for that environment but they have their place.

Yea this design in itself is perfectly safe/usable etc so long as it’s designed correctly. One of my most enjoyable things to do is watch BigClive continue to find lower bars for sketchy/unsafe products and watch then as he spends 3 minutes to sketch out a PCB that’s better in every way and includes the added bonus of no longer being deadly if you touch it while charging

The deadly Dalek that sent mains power through the USB port’s metal facade, and all because of a little LED light that served no purpose was connected in a way that made the whole unit unsafe ...that was one of my favorites


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[rsjsouza]

Or in the case of the el-cheapo Mastech MAS830L (M830B-class), the rotary switch simply disconnects the other input from the jacks, giving zero uA or mA if the probe is on the A jack. 

But does it do the opposite, i.e. disconnect the A jack? 10A through the rotary switch?

Sorry, I guess I didn't write this well. What I meant is that "(...) the rotary switch simply disconnects the A/D input from the jacks (...)"
The load is still connected and current is flowing through the beefy 10A shunt, but the meter does not give false readings. IMO this is a more sensible approach.

BTW both UT-61E and UT-136C give weird readings just like the ones on the OP. The UT-61E halves the measurement when the probe is connected to the A jack and the switch is in the mA/µA positions (0.130A becomes 65.0mA or 65.0µA).

Right and the UT61E has a separate Jack for mA/uA right next to the 10A fused jack, so it’s not weird at that point is it?

We know the devices in question aren’t auto ranging, therefore it relies on the selection we make to correctly route the current/interpret the values and display them accordingly

And we lastly know that there’s a Jack for the high current mode, and a Jack for the lower range, so it would seem logical that selecting a range and using anything but the terminal intended to be matched up w/that mode will have some effect on the resulting values,

I am not entirely sure what you mean here. My post is not pointing a finger to the fact the user is making a mistake, but instead what the meter does when it happens. Both Uni-Ts show an erroneous measure just like the OP, with a special distortion on the values showed by the UT-61E. 

as budget device makers aren’t in the business of using more components than needed/added complexity for no reason at all.

And yet, the cheapest of them all does a much more elegant solution in my opinion.

[rsjsouza]

And the Fluke 27/FM (the ancient grey/brown one) also disconnects the ADC input, just like the Mastech MAS830L