Which measurement is actually failing are there actual readings you can report ?

I'd expect a tester checking an  extension lead to be doing 3 distinct tests
1) resistance of copper conductors - should be low, sub ohms
2) resistance of insulation - should be high, megohms  and
3) polarity/ cross-over checks - and that should be 'no crossovers'/

Which test is actually failing may be a clue.

Mike.

Nothing that complex.  A simple Pat test using the power cord button option. (4th button on bottom) 

Older tester: passes.  New tester and both units fail.  Wondered if anyone else had seen this? 

Do the 'Earth continuity'/'Insulation resistance'/'Polarity' lights not indicate which test failed?

   - Andy.

It has to be that complex - what do you imagine it is doing on your behalf? When a part is failed how to you know what fault to repair ?

Here is the manual for that model

Which of the tests in that manual are you running ?

Mike.

Does the new model show a pass if you simply test the as-supplied IEC lead  (rather than one from an appliance) using the power cord test option ?

If so, I would suggest  it could be a faulty product or batch?

If not,  you could also ask the manufacturer if they have made any changes to the pass/fail criteria with the newer model (changes do sometimes happen to products).

Scratch that, I found a manual for an older model, and the fail thresholds are apparently the same:

If it helps, using those thresholds, the theoretical maximum lead lengths that result (for the different csa from 0.5 sq mm to 1.5 sq mm) are:

The lead lengths (10 m, 25 m, 40 m) appear to be roughly based on 1.25 sq mm csa cable.

Hi Everyone,

thank you for taking the time to reply and make suggestions. Exactly why I popped the question on here.

Its the polarity test that is failing on the new model compared to the old model and we have been talking to technical support at  the suppliers too. They are scratching their heads.

We have tried lots of leads from "kettle" leads to extension leads. pass on old model, fail on new model. 

Intrigued. 

Juts to add that we have checked plug tops, sockets, fuses etc.   Still fail on new kit and not on old model. 

Gerard O'Neill said:

Its the polarity test that is failing on the new model compared to the old model and we have been talking to technical support at  the suppliers too. They are scratching their heads.

Yes, that sounds odd - particularly if you have checked the connections yourself with a multimeter, and it checks out on the old tester, it really does seem like a question for the manufacturer.

I wonder whether they have a production line with someone making an error with internal wiring swapping L and N connections? It has been known in the past (and on many appliances, it doesn't matter).

'Polarity' in this sense means the tester thinks that L and N are reversed.

To prove this you could rewire one plug to make a lead where L and N are actually crossed (so connect Blue to the fuse, Brown to the neutral pin) and see if the recalcitrant tester passes it.

Once you have verified this, then put it back properly soonest of course !

If that deliberately reversed lead was a 'pass' that would be the smoking gun that the tester has an internal wiring error.

At which point you present your evidence to the makers and demand they give your money back and if  it looks like more than one affected unit, also issue a product warning or maybe a recall.

Trading standards (via Citizens Advice Bureaux these days) should be interested, but would probably not consider it very serious.

Mike.

If that did prove to be the cause.... it should lead to some very serious internal questions for the manufacturer about their own end-of-line testing!

Yes, of course human error can & does/occur... but there should be sufficiently vigorous testing in place to ensure that such errors are detected & don't leave the factory.