Class III equipment is defined as that in which protection against electric shock relies on the fact that no voltages higher than safety extra low voltage (SELV) are present. SELV is defined in turn in the relevant standard as a voltage not exceeding 25V ac or 60V dc.
In practice such equipment is either battery operated or supplied by a SELV transformer.
If battery operated equipment is capable of being operated when connected to the mains (for example, for battery charging) then it must be safety tested as either Class I or Class II equipment. Similarly, equipment powered from a SELV transformer should be tested in conjunction with the transformer as Class I or Class II equipment as appropriate.
It is interesting to note that the current IEC standard relating to the safety of medical electrical equipment does not recognise Class III equipment since limitation of voltage is not deemed sufficient to ensure safety of the patient.
Seems reasonable to me.
In other words, if the complete equipment (
ie, together with any power supply or charger) includes a mains power plug, then it (the whole thing) should be tested for electrical safety.
In practice, I doubt that your students will ever encounter Class III equipment in any hospital or clinical environment. But if they do, then my advice to them would be to remove it!
