Multimeter safety voltages ? - Page 1
Forum section: electronics / testgear

author: wael
author_rank: Contributor
timestamp: June 02, 2018, 03:29:18 pm
content: Hi,I'm kind of confused with multimeter voltages ratings. Each meter(attached) has two different voltages ratings printed on it. Anyone knows why ?Please check the attachment.The grey one is RadioShack 22-811The green one is kyoritsu Kew 1011Best regards,Wael

author: GEOelectronics
author_rank: Regular Contributor
timestamp: June 02, 2018, 03:47:32 pm
content: Some links to help:http://www.ni.com/white-paper/5019/en/and search online:"ABC's of DMM safety" by FlukeGeo>K0FF

author: joeqsmith
author_rank: Super Contributor
timestamp: June 02, 2018, 04:27:04 pm
content: Looks like there are four in the first picture. One appears to be a case insulation rating, one the maximum the inputs to the meter and the other's safety.

author: Fungus
author_rank: Super Contributor
timestamp: June 03, 2018, 10:14:13 am
content: The individual voltages apply to the parts of the meter where they're printed.I see this one as the maximum voltage you should apply to that terminal when you're holding the meter in your hand (ie. YOU are the earth point at the bottom of that indicator)The 600V indicated on that meter is obviously maximum 600V between COM and V.

author: stj
author_rank: Super Contributor
timestamp: June 04, 2018, 10:40:59 am
content: it does not state the maximum voltage when testing current.a common problem, but dangerous.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 04, 2018, 11:56:38 am
content: Quote from: Fungus on June 03, 2018, 10:14:13 amWhat if the meter is hung by a magnetic strap to a grounded panel? Are you then allowed to exceed this, after all you are no longer the earth point? I wonder how they test for this in a lab. Hard to believe any meter would break down through the case at even a KV.

author: Fungus
author_rank: Super Contributor
timestamp: June 04, 2018, 12:03:45 pm
content: Quote from: joeqsmith on June 04, 2018, 11:56:38 amYep, it doesn't make much sense to me.eg. Can you reverse the leads and be safe?

author: stj
author_rank: Super Contributor
timestamp: June 04, 2018, 01:06:47 pm
content: given most people will have a probe in each hand, i think any talk about insulation-breakdown should start with the probes and cable!

author: Neilm
author_rank: Super Contributor
timestamp: June 05, 2018, 06:42:15 pm
content: Quote from: joeqsmith on June 04, 2018, 11:56:38 amClearance is the issue. If the distance through the case join is too low it will breakdown to your hand through the join of the case rather than punching through the plastic.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 05, 2018, 07:03:33 pm
content: Quote from: Neilm on June 05, 2018, 06:42:15 pmHard to believe any meter would break down through the case at even a KV.

author: wael
author_rank: Contributor
timestamp: June 05, 2018, 08:49:12 pm
content: May be they mean the high transient voltage ? I don't know.....

author: joeqsmith
author_rank: Super Contributor
timestamp: June 05, 2018, 11:52:05 pm
content: Quote from: wael on June 05, 2018, 08:49:12 pmThe manual should be clear about what they mean. Page 12, Page 16 6-1.https://www.kew-ltd.co.jp/en/download/pdf/manual/english/1011_IM_92-1824C_E_L.pdf

author: Neilm
author_rank: Super Contributor
timestamp: June 06, 2018, 06:12:47 pm
content: I don't remember what transient is put onto a 300V cat III system - probably about 4kV. Lets say that would need 5mm clearance, so if there is something conductive within 5mm of the outside of the case through the join it could jump to the users hand if the transient happens.Quote from: joeqsmith on June 05, 2018, 11:52:05 pmManuals tend to be written by marketing people who don't know the fine detail.

author: Fungus
author_rank: Super Contributor
timestamp: June 06, 2018, 06:33:32 pm
content: Quote from: Neilm on June 06, 2018, 06:12:47 pmGood guess:

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 12:51:56 am
content: I linked the manual and provided the page numbers. Was clear to me. Still hard to believe any meter would break down through the case at even a KV.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: June 07, 2018, 01:53:46 am
content: Quote from: joeqsmith on June 07, 2018, 12:51:56 amI think it also has to do with the thing not turning into a fire cracker and physically blowing your hand off.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 10:21:22 am
content: Quote from: JustMeHere on June 07, 2018, 01:53:46 amStill hard to believe any meter would break down through the case at even a KV.Why beat a dead horse? I want to make sure that you and others are not reading more into what I posted than what is there.

author: stj
author_rank: Super Contributor
timestamp: June 07, 2018, 10:38:53 am
content: Quote from: JustMeHere on June 07, 2018, 01:53:46 amthat gives me an idea,what would change if you had the meter casing filled with sand???would it kill an arc like a safety fuse does??

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 10:56:31 am
content: Quote from: stj on June 07, 2018, 10:38:53 amOk, well lets assume it uses some new switch technology anyway. Sand and those switches may not play well together. If the traces are so close that is can jump, the sand would not do much to stop it. Maybe they could fill it with oil rather than sand. Or, maybe just design the meter to handle the transients?I vote your post the best post of the day!! Most out of the box thinking I have seen in a while!

author: Fungus
author_rank: Super Contributor
timestamp: June 07, 2018, 01:50:30 pm
content: Quote from: joeqsmith on June 07, 2018, 12:51:56 amThe instructions are clear and match what the graphics on the meter are telling us.But ... it makes no sense. In both cases the CAT rating is higher than the "potential to ground" rating.Can I only measure a 600V DC circuit with this meter if the 'neutral' wire is at -300V DC relative to ground?(in which case it isn't very neutral, it's actually quite hostile)

author: stj
author_rank: Super Contributor
timestamp: June 07, 2018, 02:17:33 pm
content: Quote from: joeqsmith on June 07, 2018, 10:56:31 ami didnt mean any perticular meter - just in general.and obviously seals would be needed to stop it pouring out of the sockets or destroying the switches.maybe the case could have walls in it to seperate the socket area where the high voltage stuff is and just fill that with sand.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 04:41:18 pm
content: Quote from: Fungus on June 07, 2018, 01:50:30 pmI can only assume a lack of stimulant on your part or mine.From page 12: Never make measurement on the circuit in which electrical potential to ground over 300V AC/DC exists.From pate 16: To avoid the danger of getting electrical shock, never make measurement on a circuit over 600V AC/DC. (electrical potential to ground 300V AC/DC)Why do you feel you need -300V DC relative to ground to measure 600V DC?

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 04:48:29 pm
content: Quote from: stj on June 07, 2018, 02:17:33 pmI got the general statement from the get go. If you kept the sand out of the switch, maybe just keep in mind that switches have a lot of copper and in some cases, contacts are very close to one another. Expanding copper can be a fun thing to play with. Could also be deadly. Of course, there are other ways to skin this cat but never hurts to think outside the box.https://youtu.be/xLDok9Sm07Q?list=PLZSS2ajxhiQAk2Q57Obdy-2yVNF-m_huu&t=110

author: Fungus
author_rank: Super Contributor
timestamp: June 07, 2018, 04:54:14 pm
content: Quote from: joeqsmith on June 07, 2018, 04:41:18 pmWhat if I don't know which is the positive and which is the negative wire? (There's a fault somewhere, right?)I might connect the COM probe to the 600V wire without knowing it.

author: joeqsmith
author_rank: Super Contributor
timestamp: June 07, 2018, 11:34:23 pm
content: Quote from: Fungus on June 07, 2018, 04:54:14 pmIf you play with the energy levels I do, it won't matter much but then you wouldn't be posting in a thread about safety. So we can assume you are working in CAT II DC and up. To be honest, I am surprised that playing with this stuff you would not know a positive from a negative wire. Or for that matter, use equipment that was not certified. That said, your interpretation of the manual is the same as mine. Normally, I if have a question about production, I turn to the manufacture. This may be one of those cases. Let me know what they have to say.

author: floobydust
author_rank: Super Contributor
timestamp: June 08, 2018, 12:58:54 am
content: If the entire DMM was floating at say 300V, there is a shock hazard. I'm not talking about the voltagebetweenthe test leads.A multimeter's common-mode voltage rating is dictated by the insulation around pushbuttons and rotary switch, and the battery compartment and housing screws, LCD window - any opening or seam.It's relevant when measuring line-line voltages on a 3-phase power system, or those with a high-leg delta.The DMM will then have a net potential wrt ground.Also, some DMM's crash when there is a lot of common-mode voltage or noise present.A metal foil shield inside a DMM is to help prevent this, as a DMM crash can indicate the wrong voltage or zero, which is a safety hazard.I thought theold 2002Fluke 17x recallwas on this issue:"...recalling 40,000 multimeters after discovering that some of them can take up to 18 seconds to display AC voltages above 500V, possibly leading users to believe that no voltage is present, with potentially hazardous consequences."

author: IanB
author_rank: Super Contributor
timestamp: June 08, 2018, 01:10:25 am
content: Quote from: Fungus on June 07, 2018, 01:50:30 pmTake an ordinary 9 V battery and measure the voltage between the (+) terminal and ground (use the ground pin of a nearby mains receptacle or a bonded water pipe).Now measure the voltage between the (-) terminal and ground.Lastly measure the voltage between the (+) and (-) terminals.Explain what you see.

author: wael
author_rank: Contributor
timestamp: June 08, 2018, 01:15:50 am
content: Well I've to say that this is a very nice explanation from you. I don't know why this haven't crossed my mind. Many thanks !

author: joeqsmith
author_rank: Super Contributor
timestamp: June 08, 2018, 02:38:34 am
content: Just to be clear, I am having some fun with Mr Fungus and suspect that was mutual. He brings up the case where the negative supply is attached to earth. Attaching the meter's common to the negative gives a common mode of 0 volts and we can read the 600V according to the manual (assuming some sort of CAT II or less). If the leads of the meter are swapped, we now have a 600V common mode, exceeding the manuals maximum 300V limit. That was my take all along but I didn't want to let him off the hook.I think if you look at most handheld meters, you will find that the common mode actually follows the CAT rating which is what I suspect Fungus was wanting me to post all along, admitting that the meter was a POS and that they had no clue how to write a manual or mark a meter (which was already pointed out to be the presumed work of their marketing department).So in this case, the 300V meant the 300V CAT III and could have shown a max common mode of 600V for CAT II and less.For others actually trying to follow the mess, ignore my posts.

author: Fungus
author_rank: Super Contributor
timestamp: June 08, 2018, 10:02:16 am
content: Quote from: joeqsmith on June 08, 2018, 02:38:34 amAnd my point was that I don't see how that voltage can be less than the CAT rated voltage (it goes bang if you swap the leads round??)It also can't be greater than the CAT rated voltage, so that means it must beequalto it.I guess that's why Fluke mark their meters like this:Conclusion: Either the markings are wrong/misleading or the meter is completely messed up internally (the voltage can leak through the case to your hand from the COM socket but not via the other one?)

author: Fungus
author_rank: Super Contributor
timestamp: June 08, 2018, 10:09:44 am
content: Quote from: floobydust on June 08, 2018, 12:58:54 amButonlyvia. the COM socket. The other sockets can be connected to 600V, no problem!

author: stj
author_rank: Super Contributor
timestamp: June 08, 2018, 11:10:49 am
content: i read that marking as "relative to ground"so if your metering a line with negative bonded to ground at some point, it can be upto 600vBUT,if your metering a 600v line that has no ground reference there could be several thousand volts difference between the lines and ground.and bad shit could happen!!

author: Neilm
author_rank: Super Contributor
timestamp: June 09, 2018, 05:37:57 pm
content: Quote from: stj on June 08, 2018, 11:10:49 amAll CAT ratings are to ground - it has to do with the transient that can be applied to the mains.One other point - IEC61010 requires testing of all combinations of inputs at the worst case (unless the leads are not compatable). Hence current inputs will have to be tested shorting the terminals with maximum voltage and a very low impedance source.

author: floobydust
author_rank: Super Contributor
timestamp: June 10, 2018, 05:20:25 am
content: Quote from: Fungus on June 08, 2018, 10:09:44 amIf you are measuring current on the high-side of a 300V rail, both sockets (COM, A) are hazardous live.The 61010 test is basically wrapping metal foil around the DMM and doing the voltage tests:"ACCESSIBLE insulating parts of the ENCLOSURE are covered with metal foil everywhere except around TERMINALS."