Hi All, thanks for the replies. A few things are now a lot clearer.
I was concerned with some the comments stating that connection of the secondary 'low' output to earth (to create a grounded neutral), meant that the transformer was no longer an isolating transformer.
My understanding (and interpretation of EN 61558) is that isolation (or separation) transformers are so called because of the galvanic isolation between the primary and secondary windings, and that this is irrespective of output earth bonding.
The company I work for supply standard Isolation Transformers (for the UK) with the output tied to earth (unless the customer specifically requests a 'floating' output). This is because many IT (computer IT - not earthing IT) applications require a neutral line which is at zero potential (wrt earth).
I know that for an IT Isolated Power System (IPS), the isolation transformer must be ungrounded as clearly stated in BS7671 and referenced in IEC 60364-7-710 Annex to MEIGaN.
And (thanks to Nick et al), I now appreciate that grounding the secondary 'low' output, means that an isolation transformer is no longer suitable for Medical applications. And I believe (my understanding is getting stretched now!) that this is because the Earth Leakage Current must be kept to a minimum for patient protection.
But I still can't find it written in the 60601 standard that the output from a isolating supply transformer must be floating (that would make my life so much easier!!).
BTW - has anybody experienced any problems attaching PCs etc to an ungrounded Medical Isolating Transformer?
Thanks again for all your comments.
