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Low R measurement on a DMM

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PushUp:
This topic is too big, to write it down in one sentence, because anyone should have a pat tester: I couldn't believe it myself, how many electrical things in my household are rubbish and does not stand the simple PE test - and here comes another one, which I have used daily so far with my computer, as it runs without a problem: My first DJMixer!

Just as an example: This DJMixer, which is Class 1, does not stand the PE test, thus it is not save to use any longer and needs a check up!

Good to see, that both of my pat testers are showing the same values:

The Metratester 5+ (the black power outlet is only for testing purposes without mains, the white is with mains)





The Secutest Pro gives you two possibilities: The "Red Ring" is for one of several automatic test sequences such as the EN62368 for instance with saved limits, here: less than 100mOhm. When the result is above the limit and therefore not shown in green but red, you have to abort the test and cannot go any further (if you want to pay an extra sum, GMC sells you the ability to bypass this, to go any further). I could change the limit, to bypass this, but does not want to, as it is not save and correct to do so...

However, the "Green Ring" is the manual test of the Secutest Pro, which can be compared with the "Metratester 5+" itself. No measured value is coloured in "green" or "red", but simply "white" and you have to estimate the result on your own or whether you want to test any further...






There are special European Norms for testing Audio-Equipment EN62368 and EN62911 (production line) together with the known EN50678 (after repair) and EN50699 (recurrent tests):






The "Gossen Metrawatt Metratester 5+" is simple to use and has all you need. I was also able to play with a Fluke 6500-2 (therefore I know the differences to the Fluke 6200-2), I owned a "Benning ST 725" (which is and has several clones), which I sold a month ago and finally bought a used "Gossen Metrawatt Secutest Pro" for my private use, as I love testgear...  :-DMM

PS and only as a short note: My "Secutest Pro" has a successor called "Secutest ST Pro", with the newest "European Norms" already included, but as I paid for the update "EN50678/EN50699/EN62368/EN62911" to also use automatic sequences, mine is now identical to the ST-Version, so that I only refer to my unit, as there are too many other things to consider with locked and unlocked Firmware-Features as mentioned above to bypass a negative test for example...


However, the most important things are:

1. different countries may have different limiting values, allthough the test equipment is the same brand and model

2. some pat testers have no automatic test sequence (Metratester 5+) and other units have both possibilities (Secutest Pro)

3. some pat testers can only measure with 500V (Fluke 6200-2), but other units are also able to measure with 250V (Fluke 6500-2, Benning ST 725) or the way you want from 50V to 500V (Secutest Pro), to treat sensitive components with care





4. any pat tester has to measure with at least +200mA (Benning ST 725), but only some units are also able to measure with 10A (Fluke 6200-2, Fluke 6500-2) and some are also able to measure with +200mADC, -200mADC, +/-200mADC, 200mAAC and 10AAC (Secutest Pro)





5. some units have no internal clock (Fluke 6200-2), others have (Benning ST 725) and other units even have a build in database to save and document any measurement for later usage and documentation with time and date and serial number of any equipment and so on... (Fluke 6500-2, Secutest Pro)

6. with an additional piece of software IZYTRON.IQ, you can even build your own personal test sequence the way you like (Secutest Pro)



Cheers!  ;)

PushUp:
As my DJMixer is +30 years old, I was surprised, that the power cord with its poor quality, togteher with a bad earthing point, was the reason for the bad PE resistance test. After solving these issues, I can now show the rest of the EN62368 testing procedure, since the value is now smaller than 100mOhm...

Manual measurement of R PE - showing no limit:




..., before starting the auto test sequence EN62368, so that you know, that it will most likely succeed...


R PE - now with limit:




I PE AC NL & DC NL:




I PE AC LN & DC LN:




Function test:




Summary of the result:





Cheers!  ;)

pope:
Thank you PushUp  :-+

Very informative post.

However, I'm afraid that all the recommended options are a bit out of my budget for the time being....  :-\ 

I keep looking for a decent and more affordable solution though.

2N3055:

--- Quote from: PushUp on April 03, 2023, 06:10:54 pm ---

--- End quote ---

Good post!

PushUp:
Yes, money is always the decisive factor! However, even more important is the wording: Don't save at the wrong end! "In german we say: Nicht am verkehrten Ende sparen!"

My example: As I wanted to save money I bought the cheap ZD-915 desoldering station from a german reseller for about 80 Euro. You cannot expect any build quality for this price, BUT you should at least expect promised material with 0.75mm² copper inside, to ensure safety. I have never ever seen such a bad PE resistance for such a short length of power cord shipped with this package...

With this power cable it is impossible to pass any test and this does prove, that any sticker, which should guarantee safety is bullshit! The cable is marked 0.75mm², but this cannot be the case with 315mOhm:




When something goes wrong, it is always a chain of unhappy circumstances, but when it happens, you would like to be on the safe side!

This power cord is from my Weller Solder Station and has the same length and thickness, but only 72mOhm:




A cheaper possibility to be on the safe side, is to use an Insulation Tester. However, this testgear measures with +300mA (here: 312,1mA) in the low Ohm setting, so that I don't know, if this is still OK, when it comes to a problem or an accident with your audio equipment:




My piece of copper is so thick, that is has a good connection inside the plug and does not play any role as I wiggled around to get a good connection point. Compared to the 315mOhm from above 320mOhm is a good hint, that the values are at least plausible and therefore right:




...and just as a comparison, that it is always better to build your own power cables with 1.5mm² thickness: This testing cable is 6m long, has a switch, a power outlet, 1m long testleads and several wago inside, together with the usual spring connection points and has only 74mOhm:






Cheers!  ;)

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