In answer to my original question, I conclude the PAS may be by powerful electric motor, on rack or steering column, controlled by ECU using data from ABS and steering wheel position. I wonder how powerful - what size fuse and cables?
The fuse is usually large - 40A or even 60A. What it actually pulls (max) is probably nowhere near that, as we all know the fuse is there to protect the wiring only.
I looked at Astra-H PAS details. 2 types fitted, depending on engine. On lighter engines, its the same TRW electro-hydraulic fitted to some later Astra-G models. No integration with other systems. On heavier engines, its a ZF system, and sits on the HS CAN, and obviously chats away to all the other systems, enabling further enhancements and features.
Obviously, TRW is now part of the ZF Group, just to confuse everyone
The docs I had to hand only didn't cover the refresh, or Astra-J/K, so didn't see any info on the pure electric stuff.
Marginally more complex as the Astra G dumb passive system only hung around for a few years (in fact there were three evolutions fitted to the G!).
It then evolved such that it had diag capability and also took in speed info etc, its this type that was fitted to many H's.
All the systems will stop operation when Vbatt is below a certain value so if the alternator is goosed, battery very low etc then you get no PAS.
Generally the column mounted setups are only on smaller lighter cars and the heavier ones have rack mounted