Multimeter CAT ratings - Page 1
Forum section: electronics / beginners

author: cowboy303
author_rank: Regular Contributor
timestamp: February 10, 2012, 02:13:52 am
content: HiThis might sound silly but I've been Googling it for the last few days and can't find the answer (that I can understand).I got this Multimeter from a Friend It's a old Fluke (8024b) It has no CAT protection or is CAT 1 rated if understand it right.I really don't want to blow it up but I don't want to put it in the corner and never use it so my question is this:can I use it to measure 12V car batteries or even 24V batteries?If it's rated for 750V AC and I shouldn't measure mains with it is it that mains can give voltage spikes above 750 volts AC?And in general the higher CAT rating it is the higher voltage spikes it can take without blowing up and more protected to high voltage on the wrong range?If I'm wrong any where in the above please let me know I'm new to this and would really like the help.Thank you very much.

author: PeterG
author_rank: Frequent Contributor
timestamp: February 10, 2012, 02:27:37 am
content: This may help you understand these rating better.http://zone.ni.com/devzone/cda/tut/p/id/5019Regards

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2012, 03:02:57 am
content: I believe this question is a continuation from this thread:https://www.eevblog.com/forum/product-reviews-photos-and-discussion/fluke-8024-bextech-530-multimeter/I've re-linked it here for continuity.Although in theory a 12 V or 24 V car battery circuit is a "safe" circuit--meaning that no unexpected high voltage surges are likely to come along and blow up your meter--these are still dangerous supplies. The reason is that an accidental short circuit on a car battery can produce a current of several hundred amps (maybe 300 to 500 amps!). This amount of current will vaporize thin wires and make thick wires glow white hot. If you happen to be touching such wires you will get badly burned.So you can use such a meter to measure voltages in a car electrical circuit quite safely, as long as you keep the meter on the voltage range and do not try to measure currents.But it is a really bad idea to take a car battery out of a car and use it as a power supply for experimental circuits. There is far too much power available. For experimenting it is much better to use a current-limited electronic power supply, or to use small batteries.As for the meter, all of us like to test our meters by measuring the mains with them. But resist the temptation to do so unless you have a real need, and if you do, make sure you are wearing safety glasses and leather gloves. Then if the worst does happen you will not get flying bits in your eye or burns on your hands.

author: cowboy303
author_rank: Regular Contributor
timestamp: February 10, 2012, 03:42:04 am
content: Quote from: PeterG on February 10, 2012, 02:27:37 amThank you it does help very much

author: cowboy303
author_rank: Regular Contributor
timestamp: February 10, 2012, 03:50:42 am
content: Quote from: IanB on February 10, 2012, 03:02:57 amThank you very much and yes it is a continuation of that thread I did some research and didn't want to open it up again after it was closed for a few days and the title didn't match the question. hope I did the right thing.Thanks again

author: mobbarley
author_rank: Regular Contributor
timestamp: February 10, 2012, 03:53:03 am
content: As long as your current ranges are suitably fused you won't have a problem with car batteries etc.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 10, 2012, 07:22:41 am
content: People used meters safely in their thousands over tens of years before CAT ratings appeared.Their development followed the development of a more litigious society,coinciding with the greater use of handheld DMMs,which put anypossible breakdown in the operator's hands,rather than on the bench or floor,as was common with most of the older VOMs.Fortunately,the same period included the development of more effective protective devices which,along with other design improvementsdiminished the possibility of injury in the event of an accident.If you are buying a new meter,it is better to err on the side of caution & get a high CAT rating.Among other things,they protect you should you do something incredibly stupid,such as connecting a meter in the Amps,or Ohms ranges across a high voltage,high current source--like the AC mains.That said,the Fluke 8024B will test virtually anything you want,but just remember,it doesn't have this extra layer of protection.Many people get all bent out of shape about "high energy" transients on the AC mains,but the general public uses electrical appliances,including such handheld devices as shavers,hairdryers & mixers, in astronomical numbers,with only the tiniest percentage of damage,let alone injury from such sources.

author: PetrosA
author_rank: Frequent Contributor
timestamp: February 10, 2012, 04:14:19 pm
content: Quote from: vk6zgo on February 10, 2012, 07:22:41 amIt's not litigation that led to CAT ratings, but the study of arc flash incidents, which really only got started in the 1980s.The reality is that in most cases, a residential service (beyond the main panel/fuses) doesn't have enough available fault current to create a serious arc flash. You can get a small flash, but rarely will it grow into a full blown, dangerous one. The greater threat is shock hazard.High transients do happen in residential, though, so it's something to keep in mind, whether it's from a lightning strike, transformer fault or higher voltage primary lines coming into contact with lower voltage primary lines as a result of a vehicle damaging a pole etc. Obviously the risks are greater if you live in an area where the majority of power lines are on poles vs. underground.Oh, and forgetting to switch the leads back to COM/V after measuring current is incredibly easy to do

author: Neilm
author_rank: Super Contributor
timestamp: February 10, 2012, 04:30:13 pm
content: Quote from: vk6zgo on February 10, 2012, 07:22:41 amIt is not the CAT rating that does this - it is the fact the meter meets IEC61010. This standard requires that the meter be safe in the event of mis-connections - indeed part 030 (test and measurement) requires mis-connection tests.QuoteElectrical sockets are rated at CAT II. The transients for this is a fraction of what a CATIV situation is. Generally, mains circuits require 3mm clearance between tracks to cope with those transients.Neil

author: IanB
author_rank: Super Contributor
timestamp: February 10, 2012, 07:48:01 pm
content: Quote from: Neilm on February 10, 2012, 04:30:13 pmBut how many home users are going to encounter CAT IV circuits? I think it is correct to say that UK law forbids anyone who is not a properly certified electrician to open CAT III or CAT IV cabinets or even touch that wiring. Probably true in other jurisdictions also. So anyone following the rules and applying proper caution will only be testing CAT I or CAT II circuits.

author: Tony R
author_rank: Regular Contributor
timestamp: February 10, 2012, 08:13:22 pm
content: Fluke has a nice document "The ABCs of multimeter safety"support.fluke.com/find-sales/download/asset/1263690_6116_eng_h_w.pdfit covers cat ratings with a very nice photo on page 2

author: Unknown
author_rank: Unknown
timestamp: February 10, 2012, 08:58:15 pm
content: Quote from: IanB on February 10, 2012, 07:48:01 pmIn many non-nanny states, working on electric circuits without training is allowed as long as you're not doing it professionally. It's hard to regulate people doing their own wiring, though insurance companies may require an electrician to certify it. Depending on the length of the wiring between your sockets and a high energy circuit, like outside overhead lines, the socket may be CAT III. Are untrained people allowed to work on this socket? Maybe not. Is anyone going to measure the wiring from the socket to the service entry? No.

author: cowboy303
author_rank: Regular Contributor
timestamp: February 10, 2012, 11:38:41 pm
content: Thank you Tony RI don't know why I didn't find that link before. It makes everything very easy to understand.And thank you every body.You guys gave me more info in a day then what I found out from Google in a week. Thank you all very much

author: vk6zgo
author_rank: Super Contributor
timestamp: February 11, 2012, 01:14:48 am
content: OK,I'll give you the limited current capabilities of home GPOs---BUT!If there arevoltagetransients which could cause much higher currents in more capable circuits,andthey happen often,theresulting damage to mains operated equipment (OK,not injury) would be very much more common.I'm not disputing that the CAT ratings are a good thing,what really annoys me is the implication that people who used VOMs & DMMS tomeasure mains voltages,& the Engineers who designed them,before these existed were either ignorant or stupid.Radio & TV transmitter Techs quite commonly used things like AVO 8 VOMs & early Beckman DMMs to measure volts at the main breaker panel.---Nothing before that except the power company!Did the meters blow up---no they didn't!A novice will post a question on whether they can use an XXX DMM to measure mains voltages,& is immediately confronted with an avalanche of stern,fatherly injunctions against doing so,coupled with links to numerous sites showing the various CAT ratings.The more extreme comments seem to doom the OP to a life of reading the sort of voltages which would be found in an old style portable transistor radio.Perhaps something like this would be a better answer:- "This DMM can be used for most testing situations you may encounter,butit was manufactured previously to the use of CAT ratings(link),& measurement of mains voltage should be approached with caution".Many of these older units may well have better capabilities than some of the new crud which have CAT numbers coming out of their kazoos,because they were designed to sound engineering principles,& not just to meet a specification.

author: Lightages
author_rank: Unknown
timestamp: February 11, 2012, 02:10:05 am
content: After reading vk6zgo's posts on this, I think I have to agree on his viewpoint. I too have pontificated on the CAT issue but I think I need to step back a bit. I don't think the paper clips I used to stick into wall sockets when I was 5 had any CAT rating. Probably any meter from most companies with a reputation for reliability should be safe for almost any home use.Now having said that, the CAT ratings do have a reason to exist. If you do encounter a unexpected voltage or high energy surge you are less likely to lose a hand. But it would take doing something stupid like connect a meter across a house feed with the probes connected in current mode to present the kind of energy that could harm someone. If someone is careless enough to do this, then maybe Darwin should have his way anyways! I have seen this done and the multimeter in question just flashed inside and maybe a bit of a bang and the stupid electrician suffered nothing but shame and soiled underwear. He was asked to leave my house the next second.

author: PetrosA
author_rank: Frequent Contributor
timestamp: February 11, 2012, 02:43:19 am
content: Quote from: Lightages on February 11, 2012, 02:10:05 amActually, no one's likely to lose a hand from a dead short in a DMM working on a residential feed. There just isn't enough current available to start and maintain an arc blast in all but a very few exceptions (large mansions with 600A-1200A three phase services - probably not too many forum users live in houses like that).I guess enough of us electricians are "stupid" enough that nowadays almost every reputable DMM manufacturer sees fit to build in some kind of lock-out or warning system for the test sockets. It must be all the alcohol we consume or pot we smoke out in the truck on our breaksMaybe the electrician at your house really was incompetent, but that kind of mistake happens to all of us at some point in time and I'd hesitate to kick someone out just on that basis.

author: ModemHead
author_rank: Frequent Contributor
timestamp: February 11, 2012, 03:09:10 am
content: Quote from: vk6zgo on February 11, 2012, 01:14:48 amI have a first-generation Fluke 87. It has no CAT ratings, only a red lightning bolt and "1000V MAX" on the front. Consider that versus the UT71 model recently dissected on another thread here, with the somewhat "optimistic" CAT ratings written all over it. I know which one I would prefer in a high-energy situation.@vk6zgo: Well said. All of it.

author: Lightages
author_rank: Unknown
timestamp: February 11, 2012, 03:15:01 am
content: Quote from: PetrosA on February 11, 2012, 02:43:19 amBased on the fact that he was in my house to inspect MY wiring job so that it could be passed for regulations, I think I was justified.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 11, 2012, 04:19:19 am
content: Quote from: PetrosA on February 11, 2012, 02:43:19 amSome of us work in industrial situations with similar capability--TV & Broadcast radio sites are an example.I guess the point is that Electricians work with the AC mains all the time,often in high-energy situations,whereas most Techs &Engineers, although we may do it quite often,never become quite as familiar with mains work,& approach such situations with great caution.Electricians get around the "familiarity breeds contempt" problem by using defined rules of behaviour when dealing with high-energysystems,including the use of specified equipment,CAT ratings,etc.They pretest meter operation on the voltage scale with a known source.If they are to blow their meter sky high,or have it give a false reading,it is much better to do so with a limited energy GPO,than across phases on a 3 ph supply circuit.Very occasionally,they get caught out when dealing with ordinary household wiring,but very seldom indeed with the "big stuff".An Engineer or Tech,looking at the mains input to a piece of equipment is in a very different situation,as they are probably only spending a minor part of their time doing this,with the rest of the time digging around in the rest of the device,& when they do approach the mains are usually over cautious in any case.

author: IanB
author_rank: Super Contributor
timestamp: February 11, 2012, 06:57:23 am
content: Quote from: PetrosA on February 11, 2012, 02:43:19 amWell now. When I was a child I was fascinated by electricity and used to play with it a lot. On one occasion I experimentally connected a selenium rectifier not intended for mains voltages to a 240 V 13 A mains outlet (with a 13 A fuse in the plug). The rectifier exploded with aKABOOM!generating a large flash, a loud bang, a shower of small flying parts, a cloud of smoke, and black char marks on the surface where it was sitting. All of this in the few milliseconds before the fuse blew.Now imagine if that were a faulty meter held in your hand...?There really is enough power in the domestic mains to do dramatic things.Each DMM I own has safety warnings in the instruction manual including the advice always to wear approved eye protection while using it. I wonder how many people actually heed that warning?

author: Bored@Work
author_rank: Super Contributor
timestamp: February 11, 2012, 09:47:25 am
content: What people seem to forget is that their trusted non-CAT meter didn't happen to be largely safe by accident, but because there were safety standards before CAT ratings. Your age old, non CAT rated meter doesn't immediately explode while using it, because (if it isn't a heap of shit) it was build according to another safety standard (maybe IEC 348) which was valid at the time of build.While people argue CAT ratings are nanny state, for pussies, conspiracies, they happily point to their age old meters that were also build according to some safety standard. Uhhh. Trying to "prove" that safety standards aren't needed, by pointing to instruments that were build according to older safety standards, kind of doesn't make much sense.It is not that the dangers of using a meter are random imaginations of the people who later came up with CAT ratings. The danger was always there, and the knowledge how to protect users from the danger as best as possible was codified in standards. And before there were written standards the knowledge was part of the engineering body of knowledge and was handed down from old engineers to new engineers as part of their education.Standards evolve, because people learn more about the subject. In case of the safety standards it was already mentioned that research into arcing increased the knowledge about potential dangers. Instead of ignoring that knowledge engineers went ahead and incorporated the new knowledge into standards.Your old meter, build to an older standard might or might not protect you from the newly understood danger, danger that was always there. The fact is, the old meter wasn't build to do so. If it protects you, then it does so by accident. A new meter, build to the newer standard, is supposed to protect you intentionally instead.The newer standard requires a CAT rating and printing of that rating on the instrument. So what? CAT ratings are simple groups, made so that also the not so brightest bulbs in the chandelier have a chance to identify if a meter is fit for a purpose or not. It allows to teach even drunken electricians simple rules "Work on this panel? Your meeter needs to have that CAT rating printed on. *grunt* Got that? *grunt* *grunt*".Argumenting that one did survive putting paper clips into a wall socket, and therefore safety standards aren't needed is extremely dumb. In fact, I would say the electric shock apparently had a negative impact on the brain capacity, at least this would explain the "argument". These days indeed few people die because of electrocution. This is because of safety standards, not because there isn't any danger.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 11, 2012, 01:25:13 pm
content: I don't believe I did say there were no dangers.What I did say was that the dangers were & are manageable.If the meters did not blow up,it is a fairly good indication that the previous standards were quite effective.Certainly,the CAT ratings are an improvement,but they are largely necessary because the miniaturisation of meters has removed some of the incidental protection of the old VOMs like the AVO 8,Simpson,etc,which was largely due to their large size & extremely rugged cases,which prevented handheld use,& allowed large clearances inside the device.An AVO 8,resting on the floor,at nearly a metre away from the operator,if it is cooked,is much less likely to cause injury.It is good practice,in any case,not to handhold a meter when it is being used to read mains.My main point is that we shouldn't scare people on this forum away from the mains with alarmist rhetoric.They are not children!

author: Dieselrunner88
author_rank: Contributor
timestamp: February 12, 2012, 03:31:29 pm
content: There is equipment made to work on mains (CAT II and III) and then there is equipment to work on electronics and automotive (CAT I). use the appropriate tool for the job and stop wondering if you should stick your $5 meter leads in a wall socket.I stuck a steak knife in a wall socket when I was 6 and the result was exiting and unsafe. Learn form my mistake and use the right tool for the job.