I think, i.e. generally it's accepted, that the objective of testing the earth on Class 1 electrical medical devices (or any class 1 device for that matter) is to test for earth continuity and adequate cross-sectional area, as indicated by earth resistance, but not necessarily to destruction. For type-testing to BS EN 60601-1 (general safety standard for electrical medical equipment) 1.5x the device load current or up to 25A ac, maximum, at 6Vac maximum, is used to measure this. Unfortunately at 25A it is possible to damage earth connections if the test-current is applied, to a DUT that is intended to be type-tested at a lower current, for too long.
So there's type testing and routine testing, such as scheduled maintenance or after repairs, to consider. My view is that routine testing requires lower earth-bond test current than type-testing, generally speaking. In my experience, since class 1 devices with load currents of less than 7A are common and I've not had that many problems over the years using testers producing 25A test current, then a time-limited 10A earth-bond test in the right hands is probably not going to cause many problems during routine testing of most Class 1 devices, including those with functional earths. A compromise.
Cable ratings have a big part to play in this, i.e. the cross-sectional area of 0.75mm^2 mains cable is rated at 6A continuous and 1.0mm^2 cable is rated at 10A continuous, for example. However a large number of devices are connected using 10A rated IEC320 detachable mains leads these days. Anyhow the earth-bond test current is usually time-limited. We could avoid the potential for damage due to internal heating (I^2.R) by using a pocket multimeter to test earth-bond but whilst this tests for earth continuity and may indicate a low resistance that's within specified limits, it may not detect that 20 strands out of a 24 strand 24/0.2 earth cable had failed, for example.
Subsequently, under fault condition, the 4 remaining strands could fuse before the mains fuse ruptures under fault conditions, or break the next time the cable is flexed (or in the period between testing), rendering the Class 1 protection useless. Personally speaking I'd rather have a dodgy protective earth bond fail during testing at 10A, when I'm on hand to observe it whilst testing, than eventually have it fail when flexed in use....
In my opinion lower earth-bond test current means, potentially, a less effective test for cross-sectional area and potentially a less sensitive voltage measurement dervied from earth resistance x test current. The benefits of lower current may be a reduced error due to changes in voltage across the single-wire type of test circuit, as its connection resistance or test current fluctuates, reduced size and weight of safety tester due to lower power component requirements but potentially this means lower sensitivity to changes in resistance if simple measuring circuits are used.
Ideally a 4-wire earth-bond resistance measurement should be used to overcome errors due to changes in the resistance of the measurement circuit connections or changes in earth bond current. Thus giving an accurate measurement that is not influenced by the resistance of connections in the tester or due to fluctuations in earth bond current. At lower test currrents we need to measure resistance more accurately and be resolve smaller changes in test voltage in the IUT due to change in earth resistance/current.
Then we only measure the voltage across the earth-bond due to the current passing through the protective earth, not the voltage across the resistance in the tester connections if the tester is not nulled, when there are changes in test lead resistance or test conditions. We then avoid this business of having to null the resistance in the test connections every time we switch on the tester or change the earth test connection.
We need to pass current through the protective earth circuit at relatively low-voltage and current to test its integrity (earth continuity and cross-sectional area) without damaging the protective or functional earth when tested routinely. 1A is suggested in DB9801 (MHRA guidelines for acceptance testing of medical devices) so that there is least likelihood of damaging devices on acceptance/commissioning. For routine testing in Austria and Germany I believe 200mA may be the standard earth-bond test current for medical devices (DIN VDE 0751).
When currents approaching 25A pass through the protective earth circuit in Class 1 equipment and the resulting voltage is limited to 6Vac then internal electronics shouldn't be affected. However some devices with functional earths may have sensitive components in series or voltage-sensitive components (diodes, resistances, "zero-Ohm" links or fusible links) connected between the functional earth(s) and "parallel" protective earths so it may be possible to effectively "short together" and fuse any parallel functional and protective earths internally as high test currents divide in these circuit paths.
