Voltmeter Safety (Tegam) - Page 1
Forum section: electronics / beginners

author: metrologist
author_rank: Super Contributor
timestamp: July 18, 2017, 11:07:31 am
content: I was reading the other thread that sort of derailed into a discussion about the safety (CAT) rating of meters and wonder how my Tegam model 125 compares in terms of HV safety with the common meters one may have, such as Fluke 87, UT210E, and those particular AN8000 series?There is another version that carries CAT ratings, but mine does not. ?https://www.tegam.com/shop/electrical-safety/125/125voltman-trms-voltmeter-with-continuity-tester/I felt safe using it to probe around house mains, and still do, but puzzled that it carries no formal safety ratings.

author: alm
author_rank: Super Contributor
timestamp: July 18, 2017, 11:15:45 am
content: According to the safety document on their website the Tegam 125 was designed in 1988. Given the reputation of Tegam as a company where obsolete instruments go to die, I imagine it has not been updated since. I believe that 1988 pre-dates IEC 1010 and CAT ratings, so obviously it does not conform to those standards. The same applies to the first generation Fluke 87, for example. This does not necessarily make the meters unsafe, but they do not conform to modern safety standards either.I imagine it would be safer than the AN8000 series, but it is hard to tell how they would compare to modern meters that do conform to the current version of IEC 61010.

author: jeroen79
author_rank: Frequent Contributor
timestamp: July 18, 2017, 05:31:36 pm
content: Open it up and post some good pictures of the inside.

author: metrologist
author_rank: Super Contributor
timestamp: July 18, 2017, 05:36:41 pm
content: That can be done! I had the thing open this morning because I was curious why it was not turning on. Since I do not use it much or poke around line voltage very often, I had removed the battery to avoid those kinds of problems.BTW, when I was a young teenager, I used the popular dual knob Micronta DMM to probe the mains, just to see. I had it in the wrong range or maybe one of the probes in the amp terminal. I survived but lost the meter and the probe tips melted off. Oddly enough, I inherited two more of the same meter, both dead and one with melted probe tips.

author: floobydust
author_rank: Super Contributor
timestamp: July 18, 2017, 07:14:59 pm
content: The Tegam website, manuals etc. mention nothing about product safety approvals.I see it a lot with old US companies, they avoid regulatory approvals because their laws are really loose.Kind of sad for a claimed "safety voltmeter". I can't see a lineman using them, as OHS wants safety certs.It seems to be a low input-resistance voltmeter, that's the safety aspect and 750V max. rating and no over-voltage ratings or tests.The probes have built-in PTC's but again no approvals or ratings.I avoid this kind of gear.

author: metrologist
author_rank: Super Contributor
timestamp: July 19, 2017, 06:46:02 am
content: Took a couple of pics...

author: floobydust
author_rank: Super Contributor
timestamp: July 20, 2017, 04:01:13 am
content: Looks like quite an old design, no MCU just a DVM IC and lots of support hardware, and a TO-99 IC...I think this is the 1992Tegam voltmeter patentfor the product, has more info.Uses PTC thermistors on the input divider for low input impedance and overvoltage tolerance.They advertise this for linesman use which isovervoltage Cat. IV, up to 750VQuick check of 61010 K.7 and those test voltages are extremely high. For basic insulation 12kVpk impulse test and 6.6kVRMS 5 seconds.I don't see this meeting modern safety standards. A fuse might help.

author: sleemanj
author_rank: Super Contributor
timestamp: July 20, 2017, 04:57:29 am
content: Quote from: floobydust on July 20, 2017, 04:01:13 amIt is not a multimeter, it is a voltmeter only, it doesn't have current range so even if it had a fuse a fault that would cause it to blow through the high impedance voltmeter would certainly be rather exciting I expect.