Perhaps I can throw a little light on some of these issues.
First, the latest definition of a Medical Electrical System (from IEC60601-1:2005) is a “combination, as specified by its MANUFACTURER, of items of equipment, at least one of which is ME (medical electrical) EQUIPMENT to be inter-connected by FUNCTIONAL CONNECTION or by use of a MULTIPLE-SOCKET OUTLET”. (Sorry about all the capitals – they use them in the standards where a word or phrase has a definition in the same standard). Incidentally, by definition, if you have assembled the system, that makes you the MANUFACTURER! So there you go – that makes most “stack systems” ME Systems, so no need to differentiate for the purposes of electrical safety testing.
Second, what is this “new electrical safety testing regime that has been agreed”? The only one I know of is the new International Standard agreed by the International Electrotechnical Commission (IEC) and published last month. This is IEC 62353 – “Medical electrical equipment – Recurrent test and test after repair of medical electrical equipment”. I think the UK members of the working group voted against it, but its out anyway. See
www.iec.ch/searchpub for details. Unlike IEC 60601-1 that is intended for “type testing” only, IEC 62353 is intended for routine testing of equipment in service that has been manufactured to comply to IEC 60601. I asked the MHRA what their line on it was going to be and, basically, they don’t have one at present.
However, IEC 62353 does have a line on testing Medical Electrical Systems. Under “General requirements” that apply to tests before putting into service, recurrent tests and tests after repair, it states that “Each individual equipment of an ME SYSTEM which has its own connection to SUPPLY MAINS, or which can be disconnected/connected from SUPPLY MAINS without the use of a tool, shall be tested individually. Additionally the ME SYSTEM as a whole shall be tested to avoid a situation where aging of individual equipment can result in unacceptable values.” So, its saying do both! The standard gives values for leakage currents that are common to both individual items of medical electrical equipment and to medical electrical systems. A particular value for protective earth resistance of medical electrical systems distinct from that for single items of medical electrical equipment is specified.
And, just in case you were wondering, yes the new standard is covered on Eastwood Park’s Safety Testing of Medical Electrical Equipment course and on other courses where the general topic is addressed.
