Class II With no metal

[Calmore]

All,

I recently attended a "course" and the instructor told us that when testing the Class II insulation test on an appliance with no metalwork, to hold the probe against an arbitrary part of the plastic enclosure and do the test like that.

To me, this seems like a pointless exercise. The chances of placing the probe over a part of the case that is failing invisibly seems remote. (If the case were cracked, you'd see it during inspection.)

I can fully understand probing any and all pieces of metal and screws (If present) but can't see why probing a random point on the plastic case would be a satisfactory test. It wouldn't be repeatable in any event but can't see what it hopes to achieve.

Thoughts..?

[Patnik]

Your instructor is talking rubbish and I'm surprised no one picked him up in the class for spouting such nonsense.

Some older PAT manuals referred to the practice of wrapping the whole plastic appliance in conductive foil or similar and applying the probe to this but I doubt this led to many faults being picked up unless there was visible 'tracking' on the outside of the case which is very rare .

If there is really no exposed metal work and even the earth pin is plastic then there is little point in doing insulation or leakage tests though I suspect many of us let the tester go through it's procedures anyway. The important exposed metal work some people seem to ignore on chargers and PSUs is the DC output connector and that is the proper place to stick your probe with these items.

Nik

[Calmore]

Thanks Patnik. I suppose I was starting to doubt my own sanity! (You know when someone says something and you think "that isn't right" but they say it with such conviction and everyone else in the room sits there, nods enthusiastically and writes it down...?)

Have always treated the output connector as 'exposed metalwork'.