1) Above 240V, DO NOT USE A DMM!!!
So for measuring voltage drop in a 3-PH 480VAC motor circuit you would use a....?
Answer: 1) A licensed electrician with proper training and equipment and his/her life insurance paid up....
Or, 2) A Fluke 87V while properly suited and booted and gloved and accompanied by a medical trauma team.
Yes, you are correct that there ARE certain circumstances where a DMM must be used around lethal voltages above the common mains. In those special cases, I would suggest that only a carefully chosen, well-proven and fully certified DMM like a Fluke be used.
All Chinese DMM's that I have owned and experimented with over the years are of such flimsy construction and have such questionable certifications that I would never think of using them for mains work. And I would be nervous with one even when making a casual check in a residential setting.
Now, I'm no fan boy of Fluke or any other brand. But, as some of us who have viewed the Fluke testing video where a Chinese cheapie explodes and burns when it is connected to mains while mistakenly set to the OHMS function, I have a much healthier respect for a Fluke DMM as a result.
I'm not knocking a Brymen either. But, I wouldn't buy one myself because the basic accuracy specs don't meet my preferences like the Flukes do. Neither, do I know what their performance record is when placed in use in a lethal industrial environment. I do know what Fluke's is though.
Another reason that I wouldn't buy a Brymen is that they have no brand distribution or support in the USA other than a couple of private labels.
That's important to me as I ask why a quality DMM manufacturer would avoid the lucrative U.S. market for so many years? Is it because of the potential liability that they would be exposed to if their DMM's didn't live up to their claims and started hurting users?
Maybe they, themselves, don't believe that their products could stand up to the tasks when compared to Fluke, Amprobe and a few other U.S. brands with proven track records of safety in service?
Just raising questions about DMM's being used in lethal voltage applications, that's all.