That set plan is a new one to me, thanks!
Since this was the first appearance of the Engine Room set it's fascinating to see how it was originally envisioned:
The entrance foyer was wider and seemed to have made use of the curved wall section (from Pike's cabin in
The Cage) which popped up here and there during Season One. Of course, this would have made it impossible to fit into the corridor set without a bit of clever editing, which sounds strangely familiar...
The big boxy "energiser" units are in the centre of the room and the vertical power conduit (which Evilkirk damages with his phaser) is much larger than the one in the final episode.
I think the design was attempting to reflect the description in the script, with engineering as a maze of sorts, with plenty of spaces for an intruder to hide in. The gorgeous forced-perspective tube structure would have been vastly more obscured however, which may be why the design was revised.