Products > Test Equipment
Big Clive's "Trashy" meter, unboxed ( Duratool D03047 multimeter )
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Fungus:
Edit: Discussion forked to Here: https://www.eevblog.com/forum/testgear/is-cat-ii-a-useful-rating/


--- Quote from: Someone on April 26, 2023, 07:43:45 am ---
--- Quote from: Fungus on April 26, 2023, 06:10:48 am ---You can't tell if it's a CAT II mains socket just by looking at it so what meter should you use?

--- End quote ---
Every mains socket outlet is CAT III

--- End quote ---

Fluke's notes say:
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.

I think it's a good idea to assume that a socket is CAT III when dealing with it, so that rules out CAT II multimeters.


--- Quote from: Someone on April 26, 2023, 07:43:45 am ---things plugged into it are CAT II

--- End quote ---

You're saying the difference between CAT III and CAT II is an extra 1m of cable?
EEVblog:

--- Quote from: Fungus on April 26, 2023, 03:56:58 am ---
--- Quote from: switchabl on April 25, 2023, 10:10:52 pm ---b) Yes, anyone repairing or developing mains-powered electronics or appliances will usually need CAT II only (CAT III is for electricians).

--- End quote ---

OK, let's say I'm working on a PC power supplies in a large office building. How can I know for sure if the mains on my workbench is CAT II or CAT III? Am I supposed to trace the wires in the walls back to the distribution panel and measure how long they are before deciding what meter to use? That's the only way to follow the standard.

--- End quote ---

The fact that it's a standard mains outlet on bench pretty much puts it in the CAT II range.
Anything in a fuse box or plant room is CAT III at least, maybe CAT IV
Fluke have a handy guide.


--- Quote ---Let's suppose it's a company with a few different rooms with workbenches. Will all those rooms have the same CAT rating?
--- End quote ---

Could technically depend on the distance, but a CAT III meter covers everything outside of a direct utility connection./


--- Quote ---Should a professional or a company like that even make the effort to source/purchase CAT II meters? What would be the advantage? What brand/model would you advise them to buy?
--- End quote ---

If you work on anything mains, get CAT III minimum as a basic rule.
Gyro:
It can be instructive to look at the breakers in the consumer unit / breaker panel in non-industrial settings. Standard IEC61009-1 breakers normally have a maximum breaking capacity of 6kA. It is the responsibility of the installing electricial to measure and ensure that the Zin is high enough and and the PSC low enough to fall within the limits of these breakers. In the case of my installation, the Zin is 0.12R, equating to a PSC of 2kA [Edit @240V], people often overestimate the prospective fault currents on their domestic installations, I've seen wild estimates in some threads. This does not cover short duration network induced voltage spikes of course, which are too fast to trip the breakers.

A competent electricial, in either industrial or consumer settings will ensure that they know such figures for the installation and ensure that their test equipment ratings exceed the prospective fault currents involved.
EEVblog:

--- Quote from: IanB on April 26, 2023, 04:08:37 am ---
--- Quote from: David Aurora on April 26, 2023, 02:20:41 am ---Have you got any plans to torture test any bench meters? Unless I missed it I haven't seen any so far from you. I'd be really curious to see what you find

--- End quote ---

Are bench meters supposed to be robust? In my mind I think of them as sensitive, delicate, precision instruments, things to be treated with care. Would you expect an expensive Mitutoyo micrometer to survive being chucked in a tool drawer?

--- End quote ---

I don't think I've ever seen a bench meter that is CAT III/IV rated, it's just not a thing.
e.g.
Someone:

--- Quote from: Fungus on April 26, 2023, 08:30:51 am ---
--- Quote from: Someone on April 26, 2023, 07:43:45 am ---things plugged into it are CAT II
--- End quote ---
You're saying the difference between CAT III and CAT II is an extra 1m of cable?
--- End quote ---
FFS, the division between the categories has to be placed somewhere. Do you want to colour code your cabling and outlets to indicate their voltages and fault currents? and make everyone else in the world do the same? or perhaps introduce 43 new categories so you can define the difference between 1.2m and 1.8m supply leads?

There are 4 categories, each with really simple and easy to remember delineations, the almost worst case situation for each is what the measurement device needs to withstand. Keeps it to a manageable number of certifications/specifications and simplifies worldwide compliance.
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