Surge modules containg MOV and GDT in series...how to test the MOV for leakage currnt

Hi,
On our offline product, we have Surge modules containing MOVs to Earth from mains input live and neutral.
The MOVs to earth have a series 500V GDT so that the MOVs don’t get blown when we do the to_Earth insulation test.
We want to test to see if the MOVs in the surge modules are high in leakage current after being installed for years…ie to see if they’ve been quenching transients.
We therefore intend to buy a 1Kv, 3mA power supply, and will put the 1kV from live to earth connections of the surge module with a series 1 MegOhm resistor and see what current flows in the 1 MegOhm. (We could break open the surge modules and remove the MOVs and test them but that would take some time to break open the modules.

Do you think this is a good way for us to test the MOVs?

This sounds like a standard 'Megger' leakage test that you should be doing on your products as standard.
Don't you have an insulation tester already that can do that?

Brian.

thanks, yes we do that test, and thats why we need the GDT in series with the MOV to earth....otherwise it would blow when we do the insulation test.
Problem is, now we want to test the mov's leakage current, but must get the GDT into conduction first.

Does BS/EN 60355 cover your product?
ISTR the lowest voltage test in that is 1kv if the product runs on >150v.

Still a little confused: what 'blows' if the current is limited to say 1mA?

I seem to remember this topic was discussed so time ago and the conclusion was that performance of a series GDT and MOV is just about as unpredictable as possible to define accurately. Use one or the other but both together is asking for problems. It may work OK but getting accurate and repeatable tests would be very difficult. It is the series element that should absorb surges, the clamp after it is to make it do its work if the voltage is too high.

Brian.