Multimeter CAT II Rating Discontinuation

[bdunham7]

Let's turn it around: Is there anybody here that thinks a CAT II multimeter makes any sense?

For general-purpose handheld meters, probably not.  For bench meters I suppose the CAT II/ (300V only) makes some sense because in certain areas and situations you won't be able to get away with simply not having a CAT rating.  Regulations might say that you must have an appropriate CAT rating for any measuring device connecting directly to any mains circuit.  Even current clamps have CAT ratings.

I'm still waiting for someone to show me a CAT II/1000V scenario.

[Fungus]

Seriously ? So you're saying I should throw the Keysight 34465A (CAT II 300V) and Siglent SDM3065X (CAT I 1000V, CAT II 600V) multimeters in the trash? 

Yep.

Or.... maybe you could follow the discussion and see we're talking about the type of meters that are used by electricians.

[bdunham7]

Or.... maybe you could follow the discussion and see we're talking about the type of meters that are used by electricians.

I'm sure that's what the first thought was for many, but wouldn't the rule change in the first post apply to the CAT II bench meters as well?

OK, I guess I didn't read that carefully.  I'd fully endorse removing CAT II from handheld meters intended for mains usage.  My reservations about the definition of CAT II remain.

[Fungus]

Or.... maybe you could follow the discussion and see we're talking about the type of meters that are used by electricians.

I'm sure that's what the first thought was for many, but wouldn't the rule change in the first post apply to the CAT II bench meters as well?

I think it's very unlikely that they'll ever be connected directly to mains sockets or distribution panels.

[bdunham7]

I think it's very unlikely that they'll ever be connected directly to mains sockets or distribution panels.

Why not, at least for mains sockets?  Someone has posted that he or his employer uses a CAT II bench meter in this way--perhaps not directly to the socket, but there's not much difference between test leads and a power cord.  So if you took away that CAT II rating, some jurisdictions may have regulations that would not allow such an instrument to be connected to mains power.  And the rule change appears to do just that if it applies to all multimeters, not just ones sold to electricians. 

[J-R]

Quick reminder, the CAT II labeling removal only applies to handheld DMMs, according to what I posted previously.  I have not seen anything yet that states the rating itself is going away or changing otherwise.

[joeqsmith]

Quick reminder, the CAT II labeling removal only applies to handheld DMMs, according to what I posted previously.  I have not seen anything yet that states the rating itself is going away or changing otherwise.

[bdunham7]

Quick reminder, the CAT II labeling removal only applies to handheld DMMs, according to what I posted previously.  I have not seen anything yet that states the rating itself is going away or changing otherwise.

Do you know if that is what happened to CAT I or did that go away entirely?  I've never understood how CAT I was applied anyway--you see CAT I/1000V on meters that are explicitly not rated for 1000VAC.

[Fungus]

you see CAT I/1000V on meters that are explicitly not rated for 1000VAC.

Clue: Some meters are incorrectly labelled.

[J-R]

Since the CAT ratings are safety ratings, it seems logical to me that you could have a device rated for CAT I 1000V but not actually be able to measure it. Although maybe that is not allowed, but without the full document I can't say for sure.

[bdunham7]

Clue: Some meters are incorrectly labelled.

    Say it isn't so!

[alm]

Clue: Some meters are incorrectly labelled.

    Say it isn't so!

What is incorrect about that? With surges as defined by CAT II 600V and CAT I 1000 V between any two inputs, the meter won't injure the user or explode. Do you have evidence that those safety claims are false? That would be a major case of fraud I wouldn't expect Fluke to commit.

[bdunham7]

What is incorrect about that?

I'm not saying it is incorrect, I'm saying it is confusing--at least to me.  It's a CAT I/1000V rated meter that can't measure 1000VAC.

With surges as defined by CAT II 600V and CAT I 1000 V between any two inputs, the meter won't injure the user or explode. Do you have evidence that those safety claims are false? That would be a major case of fraud I wouldn't expect Fluke to commit.

I don't think that's a correct or complete statement of the requirements.  For example, I don't believe the test procedures specify that the voltage + surge test is done on all ranges.  I'm fairly confident Fluke has done their best to apply the standard correctly, but since I don't have it I can't fully understand the details.  I'm certainly not claiming the markings are false.

 I'm not sure at all that the 'any two inputs' requirement applies to bench meters or CAT I/CAT II only devices.  And IIRC, Flukes position, or at least their design standard, is not simply that the meter must not explode and injure the user.  Here's another model, from the same manfacturer where it seems clearer to me.  It also seems evident that the CAT ratings are not meant to apply to the 4W sense jacks. 

[tautech]

What is incorrect about that?

I'm not saying it is incorrect, I'm saying it is confusing--at least to me.  It's a CAT I/1000V rated meter that can't measure 1000VAC.

Normal industry ratings.
1kV rated meters generally max out at 750VAC.
These do:

[Fungus]

Since the CAT ratings are safety ratings, it seems logical to me that you could have a device rated for CAT I 1000V but not actually be able to measure it.

AFAIK the voltage specified in a CAT rating is a voltage that can safely be applied on any input setting.

Now we just have figure out what "safely" means - safe for the user or safe for the meter?

[Fungus]

I'm not saying it is incorrect, I'm saying it is confusing--at least to me.  It's a CAT I/1000V rated meter that can't measure 1000VAC.

What's confusing about it?

Not displaying a reading with 1000V input isn't the same as being safe when 1000V is applied.

[Someone]

Well done referring to a vague "reference" (you could have quoted but didn't). I've quoted AS61010 word for word
https://www.eevblog.com/forum/testgear/is-cat-ii-a-useful-rating/msg4833239/#msg4833239

My 'vague reference' was your link.  I'm not trying to win a debate here--your interpretation makes sense even if it is a bit arbitrary and I would be happy have such a clear and understandable rule.  Estimating the distance to my service panel is tedious.  I just didn't see any clear evidence presented.

If you tell me that these exact words appear verbatim in the standard itself and there is no language that is contradictory or gives further details that would make it less clear, I'll take your word for it.

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"

The only question I'd have is when you are determining category based on which side of the socket you are on, does that apply to all sockets or just certain smaller ones?

That standard does not discriminate between different plug in equipment, or the outlets they are plugged in to. We have some posters saying they would happily use Cat II out into some parts of their installation, and others saying Cat III is necessary on some of their outlets. Both can be true and appropriate as the standard is only a guidance not some magical 100% true rule of nature that is always correct in every situation ever.

The standard just provides for some rules of thumb, that I can point back to as accepted practice if something goes wrong. What's the problem here is a small number of posters trying to argue they can redefine what the standard is to suit their (unknown) motivations, or spread incorrect interpretations of those standards.

Yet as I'm typing this there is a user who does not have access to the standards in question is claiming to know what they say, despite being told personally, directly, in public, in this same thread, that what they are saying is incorrect. This forum is turning into a pile of incorrect information from ignorant but noisy posters, drowning out the actually correct and verifiable truth, a general problem with unmoderated internet content.

[Someone]

Quick reminder, the CAT II labeling removal only applies to handheld DMMs, according to what I posted previously.  I have not seen anything yet that states the rating itself is going away or changing otherwise.

Do you know if that is what happened to CAT I or did that go away entirely?

CAT I still exists within the 61010 standards but is not printed next to the terminals of handheld multimeters (and now CAT II specifications aren't allowed to be printed there either).

/thread

[bdunham7]

The standard just provides for some rules of thumb, that I can point back to as accepted practice if something goes wrong. What's the problem here is a small number of posters trying to argue they can redefine what the standard is to suit their (unknown) motivations, or spread incorrect interpretations of those standards.

I don't have any motivations whatsoever other than to try an understand and clarify.  If the 'standard' here is just 'guidance' that provides rules of thumb and expects you to fill in the rest with common sense, than IMO that's not much of a standard.  I don't have this standard, but other standards that I do know about or are publicly available aren't generally vague and don't require a lot of hand-waving, although you do have to read them carefully and know what all the references and exceptions are.  It might explain why they wouldn't want to publish it.   

It the standards are vague enough to allow some manager somewhere to claim that the CAT II bench meter is good enough for the scenario I laid out, then they aren't helping much.  But I'm a bit doubtful that they would be that flawed or that Fluke would deliberately (or even negligently) publish false information that clearly contradicts what you are claiming is the standard.  My best guess, based only on speculation and language from Fluke's reference, is that there is additional language specifying a single-phase receptacle/plug, not just any receptacle/plug. 

[alm]

I'm not saying it is incorrect, I'm saying it is confusing--at least to me.  It's a CAT I/1000V rated meter that can't measure 1000VAC.

Overvoltage ratings are about safety, not the ability to measure. Maybe some internal amplifier would clip, the accuracy would be severely degraded due to V^2/R heating in the divider, or maybe it would even be damaged if exposed repeatedly to 1000 Vrms but not harm the user. Again, IEC 61010 does not care if the equipment keeps working or dies as soon as you turn it on. It's a safety standard, not a quality standard.

[I don't think that's a correct or complete statement of the requirements.  For example, I don't believe the test procedures specify that the voltage + surge test is done on all ranges.  I'm fairly confident Fluke has done their best to apply the standard correctly, but since I don't have it I can't fully understand the details.  I'm certainly not claiming the markings are false.

 I'm not sure at all that the 'any two inputs' requirement applies to bench meters or CAT I/CAT II only devices.  And IIRC, Flukes position, or at least their design standard, is not simply that the meter must not explode and injure the user.  Here's another model, from the same manfacturer where it seems clearer to me.  It also seems evident that the CAT ratings are not meant to apply to the 4W sense jacks.

I think they changed that two decades ago to crack down on the "CAT IV 600V on the voltage inputs but a flimsy glass fuse with CAT I 300V for the current input" nonsense. I don't have access to the full standard so I can't give you the exact quote, but the sense terminals should at least be able to handle the max rated voltage (e.g. 1000V DC or AC peak) on all inputs and range/function settings without any danger to the user. From a 2022 draft of IEC 61010-2-030 from CDV that unfortunately only contains changes to the previous version:

In NORMAL CONDITION and in cases of REASONABLY FORESEEABLE MISUSE , no HAZARD shall arise when the highest RATED voltage or current of a measuring circuit TERMINAL applied to that TERMINAL or to any other compatible TERMINAL, with any combination of function and range settings.

See this archived page from Gossen describing how similar language was in the 2002 version. I can't find any authoritative reference saying the transient tests should also be applied to any inputs, though I've seen discussion on the eevblog forums to that effect.

[bdunham7]

Overvoltage ratings are about safety, not the ability to measure. Maybe some internal amplifier would clip, the accuracy would be severely degraded due to V^2/R heating in the divider, or maybe it would even be damaged if exposed repeatedly to 1000 Vrms but not harm the user. Again, IEC 61010 does not care if the equipment keeps working or dies as soon as you turn it on. It's a safety standard, not a quality standard.

I don't know what is in the current regulations, but I recall seeing quotes or references to specific language requiring the meter to be able to detect and display the presence of hazardous voltages even after the transient test.  There was some discussion about degraded accuracy and such, but this is clearly a safety issue as well--if a transient can suddenly cause the meter to display 000.00V when the circuit is still live, that's not good. 

I think it is likely that manfacturers could interpret all this in different ways, and one takeaway point is that just like with accuracy specifications, it is not very helpful to directly compare instruments from different manufacturers solely by their specified ratings. 

From a Fluke advertorial:

In the impulse testing phase, Fluke multimeters are subjected to repeated jolts of high voltage to prove they can withstand voltage spikes from lightning or other causes without damage to the product or harm to their users. The higher the voltage or measurement category where the product will be used, the higher the test voltage applied—up to 12,000 volts for products designed for CAT IV/1000V environments

https://www.fluke.com/en/learn/blog/safety/fluke-lab-tortures-test-tools-so-technicians-feel-no-pain

[bdunham7]

Normal industry ratings.
1kV rated meters generally max out at 750VAC.

I get it, I've seen many and I'm used to it.  I think it is unhelpful and especially confusing when you have a CAT I/1000V rating and the separate AC measurement limitation is not on the face of the meter.  If you have to read the manual to know something as simple as the maximum voltage rating, that's not optimal.

[tautech]

Normal industry ratings.
1kV rated meters generally max out at 750VAC.

I get it, I've seen many and I'm used to it.  I think it is unhelpful and especially confusing when you have a CAT I/1000V rating and the separate AC measurement limitation is not on the face of the meter.  If you have to read the manual to know something as simple as the maximum voltage rating, that's not optimal.

Yet operating the meter beyond ratings is normally met with OL on the display.

One normally expects those playing with such voltages have some idea what they are doing.
How much need a manufacturer hold the hand of their users ? 

[Martin72]

Actually, not at all, it is enough to indicate to what extent you are allowed to use the device.
I don't know where it is regulated differently, but here only trained electricians are allowed to measure voltages that go beyond what is just not life-threatening.

[Someone]

It the standards are vague enough to allow some manager somewhere to claim that the CAT II bench meter is good enough for the scenario I laid out, then they aren't helping much.  But I'm a bit doubtful that they would be that flawed or that Fluke would deliberately (or even negligently) publish false information that clearly contradicts what you are claiming is the standard.  My best guess, based only on speculation and language from Fluke's reference, is that there is additional language specifying a single-phase receptacle/plug, not just any receptacle/plug.

You're on point here, the standards do not have a string of complex clauses for the definitions of Measurement Categories, its laid out plainly as I provided direct word for word quotes of.

Yes, the delineations are not perfect but there is no perfect delineation as the world is complex. This is layers of abstraction as the Measurement Categories define the limits of the safety tests, so all that compliance to a specific Measurement Category defines is that the product won't cause a hazard within those defined synthetic test conditions.....  which have been chosen by the committees based on historical data and experience to generally cover the real world situations.

Why is it so hard for people to understand?
The standard is a specific limit that is considered representative of the real world.
There will be real world examples worse than that (but they will be very few/unusual)
There will be real world examples that are benign and never even approach the limit (common, routine, normal, typical, most situations)

Otherwise you end up with an impossible to meet standard that covers a soaking wet gorilla probing a socket outlet outside in the rain, which is connected back to the poles with some obscure 120mm2 cable, during lighting strike on the nearest pole.... and the meter needs to continue operating perfectly afterwards despite being on current mode and connected across the phases.