Author Topic: Multimeters that do not appear to meet their safety specs. (updated frequently)  (Read 153595 times)

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Offline Jasper

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How can you make that safe at 1kV? Maybe I'm just too much a noob but the though of 1kV across a 10mOhm shunt makes my hair stand on end.

As far as I can tell it's basically irrelevant -- the Cat rating applies to the voltage jack, not to the amp jacks. It would be *really* frickin' hard to design a meter that could withstand on the 10A/20A fused jack (let alone an unfused version) genuine 1 kV at a fair few kiloAmps short-circuit-current power-distribution-network-grade electricity without breaking at all. Even getting a fuse to blow before any semiconductors or the shunt or the PCB traces do is not all that easy.
 

Offline PedroDaGr8

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How can you make that safe at 1kV? Maybe I'm just too much a noob but the though of 1kV across a 10mOhm shunt makes my hair stand on end.

As far as I can tell it's basically irrelevant -- the Cat rating applies to the voltage jack, not to the amp jacks. It would be *really* frickin' hard to design a meter that could withstand on the 10A/20A fused jack (let alone an unfused version) genuine 1 kV at a fair few kiloAmps short-circuit-current power-distribution-network-grade electricity without breaking at all. Even getting a fuse to blow before any semiconductors or the shunt or the PCB traces do is not all that easy.

Incorrect, CAT applies to all inputs, though it used to be you could have different CAT ratings for each input. From what I understand, it doesn't have to survive per se. The meter has to be able to safely and fully break the current. Meaning no arc over. HRC fuses can break large currents at 1kV. So I'm not surprised that some can. Just not sure how you achieve the safe breaking without any input protection.

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Offline Jasper

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How can you make that safe at 1kV? Maybe I'm just too much a noob but the though of 1kV across a 10mOhm shunt makes my hair stand on end.
As far as I can tell it's basically irrelevant -- the Cat rating applies to the voltage jack, not to the amp jacks. It would be *really* frickin' hard to design a meter that could withstand on the 10A/20A fused jack (let alone an unfused version) genuine 1 kV at a fair few kiloAmps short-circuit-current power-distribution-network-grade electricity without breaking at all. Even getting a fuse to blow before any semiconductors or the shunt or the PCB traces do is not all that easy.
Incorrect, CAT applies to all inputs, though it used to be you could have different CAT ratings for each input. From what I understand, it doesn't have to survive per se. The meter has to be able to safely and fully break the current. Meaning no arc over. HRC fuses can break large currents at 1kV. So I'm not surprised that some can. Just not sure how you achieve the safe breaking without any input protection.

Ah: http://www.gossenmetrawatt.com/english/seiten/newsafetystandardiec61010-1since0.htm

Gossen claims that this has been the case since 2004. Since the meter in question is specced in the 2001 standard, it didn't yet have to conform to that.
 

Offline mimmus78

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Hi everybody, good news for safety.

I have on stock new revision of Brymen multimeters the BM257s and the BM867s. Brymen released the "s" version for all the multimeters series.

Both models now uses fuses rated to 1000V to comply with third edition of EN 61010-1 and 61010-2-30, 61010-2-33, 61010-31 and in the "s" version all multimeters terminals have the same CAT rating.

Tomorrow I will check what is changed "INSIDE" the BM257s and let you know.

Ciao

 

Offline mimmus78

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Here the two photos of the input protection board of the BM257(s) board:

BM257   BM257S   

They made a lot of small changes to the board and used bigger PTC and Varistors. It seems an improvement over the pervious revision.
« Last Edit: March 21, 2014, 08:38:11 am by mimmus78 »
 

Offline Lightages

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I am very glad to see that. Franky............
 

Offline Carrington

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I have on stock new revision of Brymen multimeters the BM257s and the BM867s. Brymen released the "s" version for all the multimeters series.
Hi mimmus78!

What has changed for the 867 series?
Could you take a picture of the new board?

Thanks
Carrington.
« Last Edit: April 19, 2014, 08:24:28 am by Carrington »
My English can be pretty bad, so suggestions are welcome. ;)
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Offline mimmus78

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They (obviously) changed fuses with 1000V rated and a very light modification in resistors configuration of input protection.

They are now using 4 resistors in 2x2 configuration instead of the 3 in the original circuit.

Only thing "I didn't liked" much of old design was this resistor inside heat shrinking tube, maybe it was an afterthought and this last revision just corrected it.

Good notice no other modifications where made in the other parts of PCB (no more insulation slots or traces) and this means old design was very good.

Here attached an image of the PCB.


->>>> ZOOM <<<<-
« Last Edit: April 26, 2014, 07:00:56 am by mimmus78 »
 

Offline Carrington

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@mimmus78: Thank you very much.  :-+

Quote
Old design was very good.
Yes, without a doubt.



I'll never measure over 1000V.
« Last Edit: April 27, 2014, 04:25:09 am by Carrington »
My English can be pretty bad, so suggestions are welcome. ;)
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Offline SeanB

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That is why I added the VDR's into my UT61E. Mine now clamps at 700 odd volts with safety. 2 275V varistors in series in each of the positions on the PCB
 

Offline electron_misfire

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I once bought a digitech QM1323 from Jaycar in Australia.
Supposed Cat III/600v rating but only 250 volt fuses
 

Offline WackyGerman

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Well , I am an owner of the Greenlee DM 830A , the rebadged brother of the Brymen 829 and it has 1000 V HTC fuses inside . It costs 280 € but it has a lifetime warranty . Could also buy the Brymen 829 from Poland for roundabout the half prize but it only has 3 years of warranty and maybe also crappy fuses like all of the 820 series from Brymen . Well it also has the CE self declaration on it but the CE mark is less worth than the paint for the mark itself . It is still possible to get all the unsafe UNI-T and rebadged ones of them in Germany so electricians like me have to watch out not to get one of these shitty multimeter which could blow the ass off while measuring outlet sockets or something like that . For 0 V measurements on sockets and in distributions I prefer to use one of these 2 pole voltage tester for safety reasons ( for this cases I take the Fluke T150 )
 

Offline ResR

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I have even worse multimeter I didn't added before for some reason - Velleman AVM 360. Blowed a fuse and a range resistor when accidentally got 230V to ohm's range. It has 1000VAC/DC measurement range but no way on earth I would connect it to that high voltages. The case is brittle as hell, no corrugated edges to contain the arc over, 5x20 glass fuse. It lights up a white LED with ohms measurement.
 

Offline Puffie40

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Revised: September 27 2013  18h10 UT

Extech EX330   CATIII/600V CATII/1000V  Current ranges have glass fuses rated for 250V with no warning of lower voltage (Submitted by T4P, reviewed by Dave Jones) Additional information and reviews on different Extechs show that Extech EX series are to be avoided in general. The quality control appears to be so bad that parts are coming loose inside some meters from the factory, amongst other problems.

I thought I'd crack open my EX520 (purchaced Dec 2013) to check the fuses and share a picture of the insides.  Both fuses are rated at 1000v  (:phew:), but they still have the caps and jumper wire at the input jacks.

The glass fuse mentioned in the quote makes me wonder if the glass fuses appear because the assembler ran out of proper ones, so they just stuffed a "will fit" in to get it out the door.
« Last Edit: February 09, 2015, 03:00:19 pm by Puffie40 »
 

Offline SNGLinks

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UNI-T UT60A bought in Maplins in the UK
http://www.maplin.co.uk/p/uni-trend-ut60a-autoranging-with-pc-interface-digital-multimeter-n80cb

Marked CAT III 1000V, CAT IV 600V and CE.

Fitted with glass fuses rated at 250V.
 

Offline naughtilus

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Is UL listing just a wank factor?
« Reply #140 on: March 02, 2015, 01:36:48 am »
I've been a long time EEV Blog/forum reader and YT subscriber. As a hobbyist I educated myself thanks to Dave's and several other members here that input protection is very very important.

The job of a multimeter is #1 to be safe for the user depending on application; #2 not to self destruct or damage the measured gear under normal operating circumstances; and #3 give accurate measurements, as the least important one. So I took all the "it must be UL listed" mantra to heart. For my own safety I wanted UL listed DMM as an assurance if it complies with IEC 61010-1 CAT ratings etc.

So I went and checked what is the cheapest DMM that I can get that is also UL listed.

Quote
UNI-TREND GROUP LTD   E226066
9TH FL, ROOM 901      
NANYANG PLAZA      
57 HUNG TO RD      
KWUN TONG KOWLOON, HONG KONG
Digital multimeters, Models UT60A, UT60B, UT60C, UT60D, UT60E.

Models UT70A, UT70B, UT70C, UT70D.

Model 3330.

Model CP7665.

Model CP7677.

Voltage detectors, Models UT12A, UT12B.

Models UT12C, UT 11A, UT11B, UT13A, UT13B.

Probe assembly, Model TL88-1.


Trademark and/or Tradename: "UNI-T"
Source: UL database

Hmmm. Wasn't Uni-T considered poo for safety and valid CAT ratings and no external certification, just slap that CE mark and sell by the boat load? It appears that all previous generation of Uni-T DMMs was UL listed. Go figure!

The UT60E has two glass fuses, one PTC, one spark gap package, no HV slots, cheapest jacks and cheapest leads. It says CAT III 1000V and CAT IV 600 on the unit. It got UL certified.



In my hobby I work with amplifier PSUs, so there is moderate to occasionally high energy to deal with. I got kinda discouraged at taking UL listing as a decision factor for safety. I just looked at teardown photos and picked the Uni-T UT139C. It simply looked it had better input protection although not UL certified and only self rated at 600V CAT III. I considered Extech but to me Uni-T had better QC and therefore better build quality. I bought Fluke TL71 leads to replace the stock Uni-T ones and I think this is as safe I can get for $65.

Is UL listing just a wank factor? I'm a bit confused.   ???
« Last Edit: March 02, 2015, 01:42:43 am by naughtilus »
...or is it?
 

Offline JOE1234

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Regarding the BK Precision 2709B and its 500V rated fuses, here is the reply I received from BK:

"The CAT III 1000V is rated based on the protective capability for the COM and V/Ohm input jacks which is protected up to 1000V. The 2709B meets the CE requirements.

"CE requests that the maximum measurement current must be marked on the meter, for example MAX 400mA, MAX 10A, or MAX 20A/30 sec. on the overlay around the input jacks. In addition, a symbol of exclamation mark (in triangle) is marked on the overlay to inform the user to read the instructions and the maximum rated voltage of Fuses in the manual. In CE regulations, CE does not request that the rated voltage of the fuses must be the same as the voltage of the CAT rating."

If my interpretation is correct, BK appears to be offering a mere logical excuse rather than a substantive technical explanation. I wonder what rating UL would have allowed on the product--Cat II/III 300V?

 

Offline miguelvp

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So I guess my UNI-T UT71B is really CAT III 1000 V
 

Offline Lightages

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BK Precision is WRONG. Simply wrong. If they don't understand the regulations, I would not be buying anything from them.
 

Offline Wytnucls

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The latest IEC safety recommendations IEC61010 3rd edition 2010 are only enforced in Europe under EN61010 published in Oct 2010 and mandatory since October 2013.
In the US, they were adopted later in October 2012 (UL61010) and will only be enforced from January 2018. So, in the US at least, multimeters can still be sold under the old regulations, where fuse voltage rating is not restricted.
 

Offline Lightages

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They refer specifically to CE standards, not US standards.
 

Offline Wytnucls

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They refer specifically to CE standards, not US standards.
In that case, the company should be made aware that EN61010 has changed since they last looked at it.
 

Offline Lightages

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Yes, I agree :)

And to quote the relevant clause:
"101.3.2   Protection by a certified overcurrent protection device
An overcurrent protection device is considered suitable if it is certified by an independent
laboratory to meet all of the following requirements.
a)   The a.c. and d.c.  RATED  voltages of the overcurrent protection device shall be at least as
high as, respectively, the highest a.c. and d.c.  RATED  voltages of any measuring  circuit
TERMINAL  on the equipment."
 

Offline miguelvp

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For what is worth, the UNI-T UT71 series mention that they comply with IEC61010
But their fuses are 250V as well (0.5A, 250V fast type fuse for the mili/micro Amp range & 10A, 250V fast type fuse for the Amp range)
 

Offline Lightages

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There are different revisions of IEC61010 and Uni-T maybe did actually meet an older version.
 


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