Ged,
Section A1.10 of 60601-1:1990;
If you look at the rationale for deciding whether part of a device is applied parts or enclosure then you will see what you are saying is inconsistent with the method of approaching testing of devices - I think you are confusing mechanical definitions of applied parts with electrical ones actually.
APPLIED PART:
"Applied part if the connection is essential for the normal use of the equipment, etc, etc....."
ENCLOSURE:
"Enclosure if contact is incidental to the functioning of the equipment, etc, etc......"
Considering a bed I know of no contact with users or patient that is essential for the bed’s normal operation, so I define the bed as enclosure. Non-earthed enclosure is tested for enclosure leakage, earthed items are tested separately for bond and earth-leakage. Patient leakage does not even come into it.
Just an aside: The mattress is actually an applied part in the mechanical sense isn't it? - Type B I think.
For Class1B I would test earth-bond, see what’s conductive and earthed and then any other accessible conductive parts are considered as enclosure. Then test for enclosure leakage of these non-earthed parts rather than testing for patient leakage via non-existent electrical applied parts. For class2 the accessible conductive parts should be tested for enclosure leakage as required.
In the standards the rationale actually states the procedure for assessing which are the applied parts in section A1.10. A Class 1B bed would not have applied parts according to the standard.
Just because you can measure patient leakage on a tester connected to what you think are "applied parts" does not mean that you're measuring patient leakage currents - it is more likely enclosure leakage as defined in the standard.
If you're measuring leakage via earthed parts you're only likely to see significant leakage under single fault conditions i.e. earth O/C (unless you have poor earth bond on Class1 equipment). Your description of testing class1 equipment is incomplete without testing under single fault conditions and testing enclosure leakage of non-earthed conductive parts. Hope you can see what I'm getting at.
There appear to be no maximum limits given for type B patient leakage with mains on applied part – is it, in fact, a valid test if you've got type B applied parts? Maybe your tester applies the patient leakage test inappropriately for 1B/2B devices? How do you apply the mains on applied part voltage on Class1B/2B applied parts if the applied part is actually earthed? The test must fail every time, in this case.
Sorry to harp on about it but I’m interested to hear your views and get a better understanding.
