How Not to Measure Mains Voltage


Staff member
This was a "stock photo" intended to show someone doing something "technical". Check out where the meter leads are plugged in?


The funny thing is that I think that would work "sort of" she is switched to the AC voltage range and measuring between Amps and Volts input, but the Amps input is connected by a shunt resistor to COM, so she is measuring between COM and Volts?

My question is will it read AC volts correctly or not? Apart from the fact that the lead polarity is reversed as well?



New member
Long time ago i had a nice cheap multimeter which was placarded or rated to measure at least 240 volts AC, but i did not know that the copper plating from the range switch contacts had plated off to form a circular track between all of those contacts .One time When trying to measure mains voltage there was a strong arcing sound with lots of smoke and the meter died. Better meters have milled slots in the PCB between the contact pads.


I "helped" a work colleague some years ago. He was working on a customer's one and only prototype board and was having some problems. Without being asked, I thought I'd jump in and grabbed his multimeter to measure the MAINS VOLTAGE. Can you guess what comes next?
Yes! The probes were plugged in to measure current, just like the picture at the start.
When I could see again after the flash, my job was to rebuild the damaged board as some tracks had gone away. Great relief was felt when it finally worked again!
Check the probes!!!!!!


New member
I the long long era gone, when I was learning, some rules in the use of a multi-meter had been drummed into me.
Never store the meter in the Ohms mode
Select the highest voltage range and put in away.

The mistake often made by measuring voltage when the leads are plugged in the current port keeps fuse manufacturers in business, I am sure.
I solved this by acquiring an idiot proof meter, LOL

Not only a warning is on the screen but a loud sound is emitted by the instrument.