Is it me or is testing a Surge Protection Device like testing a cartridge fuse?

I know there are testers which have SPD tests as one of their functions, which appear to be a ramp insulation test, steadily increasing the insulation test current until the SPD operates and displaying the result.

How many times could this test be carried out before the SPD fails permanently?

I cannot ever imagine the IET recommending carrying out potentially destructive testing, which is what SPD testing appears to be to me, which makes some functions on new testers unnecessary?

Sparkingchip said:

Is it me or is testing a Surge Protection Device like testing a cartridge fuse?

Sort of - they will only be rated for a certain number of guaranteed "events" at different voltage levels.

Sparkingchip said:

I cannot ever imagine the IET recommending carrying out potentially destructive testing, which is what SPD testing appears to be to me, which makes some functions on new testers unnecessary?

It's one of the reasons most industry practice now recommends limiting the number of tripping-tests of RCDs to 2 (i.e. 0.5x, no trip and 1x, 0 and 180 degrees) when carrying out initial and periodic verification according to BS 7671. RCDs only have a certain number of anticipated operations.

Sparkingchip said:

Is it me or is testing a Surge Protection Device like testing a cartridge fuse?

Sort of - they will only be rated for a certain number of guaranteed "events" at different voltage levels.

Sparkingchip said:

I cannot ever imagine the IET recommending carrying out potentially destructive testing, which is what SPD testing appears to be to me, which makes some functions on new testers unnecessary?

It's one of the reasons most industry practice now recommends limiting the number of tripping-tests of RCDs to 2 (i.e. 0.5x, no trip and 1x, 0 and 180 degrees) when carrying out initial and periodic verification according to BS 7671. RCDs only have a certain number of anticipated operations.

gkenyon said:

Sparkingchip said:

Is it me or is testing a Surge Protection Device like testing a cartridge fuse?

Sort of - they will only be rated for a certain number of guaranteed "events" at different voltage levels.

Which connects with my question, how do I know that my SPD is still working? I think the answer here is that the green flag is still showing. Do we trust it or not?

Much as you can test a fuse by measuring its resistance with a low current and not operate it (**) or indeed a high curretn for a short enough time not to warm up the fusewire, with the right equipment, you can test an SPD by by sweeping the I/V characteristic, but vary fast so there is no significance dissipation, so no internal heating and no migration of material, and so the device does not have its life shortened  by the test.

Indeed you can use changes in the turn on voltage and the rate of rise of current collected by this method, to measure how degraded a device has become by an event, if you have before and after curves for the same device. This allows you to see how well it is performing, and to  exchange the device before it fails catastrophically.

There a very few situations outside a laboratory test facility, where such an approach  is economically justifiable.

Mike.

PS

** for what it is worth, detonators for electrically operated explosives also pass a very low current round the firing loop, to indicate that the bridge wire/fusewire is intact before firing- this is very important in demolition, and other situations where explosive must be fired with close timing and/or in the right order to bring things down safely in the right direction and misfires must be avoided.

For such things a  'no fire' upper safe current, and and 'all-fire' lower limit firing current are a key part of the spec so the safety loop checks and the firing circuit are both reliable..