Isolation transformer before RPC - to centre-tap secondary or not?

I'm updating my RPC a little, rewinding the auto-transformer as an isolating transformer, intention being to increase safety by de-referencing it from local earth (transformer is a large oil-cooled welding transformer with a dual-voltage 240/415v primary winding).
I'm in the UK so one leg of the 240v is at neutral = earth potential, using an autotransformer I have a 415v-to-earth/neutral output and once rewound as an isolating transformer the 415v output will be "floating" with no earth reference.

What's puzzling me is whether adding a centre-tap to the 415v secondary has any purpose, there will be a safety earth carried through to the 3-phase side, but I'm fairly sure that the centre-tap would not be even close to a neutral point as generated in the RPC - that would have to come from a motor star point?

The machinery I have doesn't use the neutral, e.g. control transformers are 415v primary across two phases (avoiding the generated leg).

The RPC currently has a single *delta wound* 7.5 HP idler, next phase (no pun intended) will be the addition of a second idler,4 HP *star* wound - this COULD provide a neutral at lower current IF I needed one for e.g. 240v control transformers but I'm certain this wouldn't be at the same potential as the transformer centre-tap and may not even be at the desired neutral potential...

RPC output is equipped properly with 3-phase magnetic breakers and residual current disconnect (earth-leakage trip) with alarm lamps and howler as safety is a priority which is why I'm going to an isolating transformer (less, theoretically no, current on a phase-earth human load )

So... while I'm winding it, add a centre-tap or not? Add it but leave disconnected for now?

Dave H. (the other one)

I doubt that a 208V center tap would prove useful to you, it would here, as that is a common voltage.

But you might consider a 240V tap, if you ever needed an isolated source for testing something. A couple voltage adjusting taps at one end might be another consideration.

SAF Ω