Well Tony , I don't think the 16th would have been of much assistance in getting that the right way up . TBH .Only ever worked at one place that wanted electricians to have, I think the 16that that time. That was due to one of the lads installing a section of busbar chamber back to front.
This has reminded myself of an instance years ago with a BBC . We ran a sub main from a switch room to a new Nurse's Home at a hospital . I was a young sparks then , I phoned the office for them to arrange a shutdown so I could drill & fit a sw/fuse to the BBC .... drill the busbars and connect tails to them .
Supervisor makes a rare visit to site , tells me its difficult to get it shut down . He then tells me to drill the 2" hole & mount the switch . Then ....are you listening .... disconnect the earth wire from the metal bodied drill & drill the bus bars live !!!!! I'd already made my mind up that he was crazy so asked how would I bolt the cable lugs on and get two spanners in there without frying myself .
He said ..... are you listening ..... you'll be fine just don't touch earth !!! I'm still here as you may have noticed . I spoke to the hospital Clerk of Works and sorted it properly.