Marcel –
Don’t shoot the messenger! I didn’t redefine anything – the definition of the term Applied Part comes from the 60601 Standard, from which the term itself originates. Whether or not it seems logical to you, or me, the quote I gave above suggests, to me at least, that the Standard would consider the bed frame an Applied Part.
I replied to Mark’s posting merely to agree that hospital beds (or any other electrical device in the Patient Environment) should be safety tested to medical device standards. On the way I queried RL’s interpretation of Type and got sucked into this debate; (Class 1 or 2 is the device; Type B, BF or CF is its Applied Part/s). In practical terms, for PM testing of in-service hospital beds , the debate whether the bed frame is an Enclosure or Applied Part is somewhat academic – the same leakage current limits apply (as RL observed). For some medical devices the distinction between Enclosure and Applied Part is more important however, which is why I queried RL’s definitions. That aside, Mark’s original question (as I understood it) was whether, when testing beds, to apply medical device leakage current limits or the usually higher limits programmed into basic PAT testers used for testing ‘normal’ electrical devices. I agreed with Mark that the former should apply to hospital beds – and in fact to any device (TV, fan, PlayStation, ventilator, bed, etc.) placed in the Patient Environment. This would apply to the headphones in your example, which should meet the electrical safety requirements for medical devices, rather than the safety requirements for the headphones you use with your hifi in your front room at home. One of the reasons that stricter leakage current limits are applied to medical (patient-applied) devices is because an ill patient may be less able to respond evasively to electrical shock than someone fit, well and unconstrained – this consideration applies whether the leakage current shock comes from radio headphones or an oximeter probe. It makes no sense to say that it is unsafe for leakage current from a probe attached to an earlobe to exceed 0.5mA, then to permit 1.4mA from a set of headphones placed upon the same ears. The bottom-line is that any electrical device in contact or contactable with the patient (or even with someone touching the patient) should meet the safety standards required of medical devices (see 60601-1-1). Having said that, this principle is routinely violated in hospital environments – which was Mark’s original concern.
(I agree with you that for in-service PM safety testing, most faults can be identified by good inspection without use of a tester device. However for Acceptance Testing the reverse is often the case. Also with regard to your example of a Class 2, no Applied Parts test – you could probably achieve a ‘pass’ without even plugging the device into your tester).
