Hi Ian,
Yes I gathered that the dot was being used as a means of identifying where the earth was to be measured and that it was probably a means of speeding up tests and avoiding confusion - depends what you're used to I suppose. I got the impression that if there's no dot, i.e. no earth, then the operator would test to class 2, irrespective.
However there's still the issue of whether the item can be identified as class 2 with a functional earth (no dot) or if it's class 1 with no accessible earth (i.e. no dot). In either case an earth leakage measurement needs to be performed and this is usually not achieved in a class 2 test, probe or no probe, unless it's selected as part of the test (or the safety analyser detects the conductive earth pin on a class 2 device - this indicates that a functional earth is likely to be present).
Admittedly most class 2 devices don't have a functional earth, i.e. conductive earth-pin, but it's frequent enough for most analysers to allow for this. By introducing a dot then the point I was making was it could cause more confusion than the markings that should already be on the IUT.
I would of cause suggest that the earth clip is moved to another part of the earthed chassis for earth leakage current tests, incuding patient leakage.
Earth leakage is usually measured via the earth-pin to ground via the safety analyser, not the probe (that's used for insulation resistance/enclosure leakage/earth continuity checks), neither is patient leakage current measured via this probe.
Another point I was trying to make is that I think the earth leakage measurement, whether it's functional or protective is quite an important one that may be missed if a class 2 test is performed on a class 1 device, as you indicated in your post previously.
Saying that even if excessive earth leakage has been missed on a class 1 device during acceptance checks for example, (because it's not got accessible earthed parts, thus it's tested to class 2), I suppose if there's no accessible earth on it then under SFC (earth O/C) it's unlikely that this will present excessive enclosure leakage on the device enclosure.
But it might inject excessive earth leakage into a medical system that's interconected via common mains distribution, under NC, eh?
We see new equipment coming into the workshop on a fairly regular basis where there's a failure to keep earth leakage and associated enclosure leakage within limits (or very little safety margin) - especially as part of more complex systems including IT that can have extras fitted by the operators.
We use the evidence from safety tests to justify to manufacturers that they should provide seperating transformers or replace components within systems that may compromise safety.
We can only do this by applying the correct tests to medical devices to establish a baseline for subsequent testing irrespective of whether they're going to install seperation, add a higher specification component, or alter the system in some way.
