Products > Test Equipment
Is CAT II a useful rating for a multimeter?
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Fungus:
The is a branch from another topic where I was wondering if "CAT II" is a useful safety marking.

The standard says that:

CAT III:
Appliance outlets with short connections to service entrance

CAT II:
Outlets at more than 10 meters (30 feet) from CAT III source.
Outlets at more than 20 meters (60 feet) from CAT IV source.

( ref: https://www.fluke.com/en/learn/blog/safety/multimeter-guide )

So, given that:
a) There's basically no difference in price between a CAT II multimeter and a CAT III multimeter.
b) You can't tell what rating a mains socket is just by looking at it so you have to assume it's CAT III.

What use is CAT II when you're looking to buy a multimeter? Shouldn't you just go for CAT III and be done with it?

To me CAT II marking just seems to say "Don't buy me, get a CAT III meter instead!"

nb. I'm not arguing that there shouldn't be a difference between CAT II and CAT III safety precautions and procedures, eg. use of PPE in CAT III environments. Maybe that should be separated out from the markings on test gear.
Fungus:
The other thing that came up in that discussion is that CAT I seems to have been deprecated and removed from the IEC standards.

To me CAT I seems like a useful rating, it says "I'm only safe for low energy measurements".

If I was in charge of removing one of the ratings from multimeters I'd have removed CAT II, not CAT I.

I'd have renamed then, too, to avoid confusion. As noted above I'd be fully behind a movement to separate the markings on meters from safety procedures when using them.
Someone:
Fluke isn't following the standard from which those categories are defined (61010) and would be misleading in typical installs in Australia and the UK (and probably other countries that I am less familiar with).

61010 measurement categories are really simple:
"CAT III is for measurements performed in the building installation"
"CAT II is for measurements performed on circuits directly connected to the [mains] voltage installation"

As mentioned in the other thread(s), its very very simple: something that plugs into a socket outlet is immediately CAT II, unless you are on the other side of safety isolation/insulation and then its up to you to know what the range of voltages/currents could be (perhaps use a more modern standard to help) and check that the multimeter/measurement tool has suitable withstand and/or breaking capacity.
EEVblog:
Easiest to just keep this basic rule, if you work on anything to do with the mains, either plugin or fixed mains wiring, have a certified CAT III rated meter as a minimum.
If you are an industrial or plant electrician you'd want a CAT IV. I'd personally use a 1000V CAT IV meter in that scenario (Fluke don't even offer one of those AFAIK)
The biggest risk though is a meter that physically has a current range and accidently using it on a mains connection.
A huge surge on a mains line that blows up your CAT III/IV meter in voltage mode in most common scenarios is so rare it borders on negligable risk.
EEVblog:
That brings up a the question, what is the safest/bested meter on the market?

Check out this bad boy, and that connector spacing  :o
https://www.hdt-electronic.com/en/products/digital-multimeter-series-200xx/digital-multimeter-autorange-and-trms-1000v-cat-iv-1000v/

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