Surge Protected Extension Lead Insulation Test

[Andy Wilson]

I have just conducted a 500v insulation test on a surge protected 230v extension lead expecting it to fail but it passed.
Can this result be correct?

[Grizzly]

Hmmm, I'd be careful on this one.
I'm presuming that the lead passed the earth bond OK, and that a polarity test followed, to validate the IR result.
Did it pass the IR test with >9.99 MΩ (or whatever your tester uses to show IR off-the-scale), or was it a figure somewhere between that and the pass limit?
If it was the former, I think I'd be suspicious of either a wiring fault, or if a polarity test proved has the wiring, then that the surge protection MOVs had failed.
If it was the latter, and a polarity test proved OK, I'd say you've just tested on of those few surge protected leads that do pass at 500V.
No guarantee it will do the same next time, though!

[Andy Wilson]

Thanks Grizzly for your reply.
I have just retested the lead and the results are shown below
Earth bond = 0.06 ohm
IR = >300 M ohm (off the scale)
Polarity = Pass
When volts are put on to the lead the "protected" LED is lit.
So I assume, from what you have told me, that the lead is one of those few that will pass a 500V test.

[Grizzly]

So I assume, from what you have told me, that the lead is one of those few that will pass a 500V test.

No, your results would indicate my 'former' example, that the surge protection may have failed, although the 'protected' LED is a mystery. Might need investigation as to how it is connected.
If a fully-working surge protected lead did pass IR at 500V, I wouldn't expect an off-the-scale result.

[Andy Wilson]

I have now tested an identical lead and the results are shown below

Earth bond = 0.05 ohm
IR @ 500V = 0.36 M ohm
Polarity = Pass

I then conducted two more insulation tests with a seperate insulation tester

IR @ 500V = 0.38 M ohm
IR @ 250V = 2.81 M ohm

Does this mean that I should pass this lead, using the result from the 250v test and fail the original lead ?

[Grizzly]

Those results are consistant with what I would expect, so it would look as if there may be something dodgy about the original lead.

[Andy Wilson]

Thanks for all your help Grizzly,
I can now go to sleep at night happy and contented.