How would it not comply? Surely if it is labelled accordingly it would be ok?
I was just thinking, I wouldn't need to link the neutral to the supply neutral, I could just disconnect the neutrals from the main neutral bar and put them into to their own isolated neutral bar that only goes via the UPS.
The earth I would still connect to the main bar though.
This is a more sensible Idea, but ideally Shankys separate board idea is the way I would do it with the UPS primary supplied from a way in your existing board , with totally separate N and E bars for the UPS supplied circuits
Depending on the UPS they run in at least two different modes, some of the better ones have three modes.
Mode 1 is just in bypass while everything is healthy, Line + Neutral (*leaving the E for the moment)
Mode 2 in UPS mode, when the primary supply has failed, depending on how the UPS is configured, this output can be totally isolated from the incoming supply (both L + N), now to the E, * depending on the type of UPS if it is of the totally isolated type it can switch the out going CPC onto one side of the now fully floating side (ie. the designated out going N) making a pseudo TNC-S (CNE link) system on the output side only, this is to maintain the protective measure of ADS.
As you can see during power failure if you joined the incoming N (main side N) to the out going N (and like wise incoming and out going CPCs) you would be creating a N-E short on the outgoing side of your now dead main DB, and also still be partially connected to the grid which is against regulations when using a backup supply.
Mode 3, some computer type UPS have a so called "brown out" mode or "power clean up mode", this mode is less clear cut, and not all makers will divulge fully how they implement this mode being a "propriety" technology aka selling point, types with this facilities are less suitable for what you have in mind.