Polarity test failure on SPD extension leads

[andynmoore]

Evening all,

This has probably been answered somewhere here, but in case it hasn't... I have a Fluke 6500-2 and had trouble testing SPD extension leads as you cannot drop the voltage to 250V using the IEC lead test button. I found a way to set up an auto test sequence to include EB and 250V insulation and disable everything else. All went well for a few tests until I had a load of SPD extension leads fail on the polarity checks!! L and N were definitely connected correctly and firmly. Any ideas what would cause this as there cannot be that many genuine failures and the fail shows in the customer report! Perhaps it's the suppressor in some of the extension leads causing it, although why would some be OK and others not...? Any thoughts would be greatly appreciated.

Thank you.

Andy

 

[James]

surge protection devices have electronics connected between live, neutral and earth.
they will fool most automated test procedures.
Simpley check polarity using an ohm meter or check it visually.
edit the report to show the true facts, not what an automatic test shows.
you are the tester, you are the expert, dont be led in to the trap of believing something that you have confirmed to be wrong.

 

[andynmoore]

surge protection devices have electronics connected between live, neutral and earth.
they will fool most automated test procedures.
Simpley check polarity using an ohm meter or check it visually.
edit the report to show the true facts, not what an automatic test shows.
you are the tester, you are the expert, dont be led in to the trap of believing something that you have confirmed to be wrong.

Thanks very much James. As you mentioned, I did a visual check on all the plug tops so I know they are correct. And wise words too, it's very easy to believe there MUST be something wrong, when in fact, you just have to step back sometimes and analyse logically!

Annoyingly on the Fluke DMS reporting software, you can change the pass status to 'yes' manually prior to generating the report, but it stills shows 'no' on the report itself next to 'Cable L-N'.

 

[James]

note, if you are using a visual check to confirm polarity, you must check both ends of the cable!!

I have never seen a cable change colour (without some obvious termination) down its length but i have seen it connected wrong at the appliance before.

 

[andynmoore]

note, if you are using a visual check to confirm polarity, you must check both ends of the cable!!

I have never seen a cable change colour (without some obvious termination) down its length but i have seen it connected wrong at the appliance before.

Yes, indeed. I noticed the extension leads I tested that failed still had small stickers over the screws on the back so indicated they hadn't been opened.

That sounds almost as bad as a coiled up and zip tied earth cable I found in the side of a washing machine... I spent way too much time trying to get an earth connection and was so heavily invested I had to open it up :-D

 

[Lucien Nunes]

The problem is the voltage at which the test instrument is carrying out the polarity test. A unit that does it at ELV won't trigger the surge protection and will return a correct result for polarity. One that uses a higher voltage can cause the MOVs to conduct enough to get confused. As it happens our three different models of tester here are all OK with surge protection but one of my colleagues has to do polarity checks with a multimeter as his is not.

 

[andynmoore]

The problem is the voltage at which the test instrument is carrying out the polarity test. A unit that does it at ELV won't trigger the surge protection and will return a correct result for polarity. One that uses a higher voltage can cause the MOVs to conduct enough to get confused. As it happens our three different models of tester here are all OK with surge protection but one of my colleagues has to do polarity checks with a multimeter as his is not.

Thanks Lucien. I set up a new autotest code to include earth bond and a 250v insulation test, but some SPD leads test out fine whilst others are still an issue. No particular brand or anything. It's very odd.