I was sent some old books by an attorney friend. A couple are the 1921 NEC and Croft's American Electrician's Handbook. A few samples of contents arer listed.
The NEC for 1921 lists #12 @ 20A. for rubber insulation, 25A. for VC, & 30A. for “other insulations.” That is for AC. For DC #12 is listed @ 30A. for single conductor cable, 25A. for 2C, 23A. for 3C, and 19A. for 4C.
The copy of American Electrician’s Handbook is fantastic! It even has a chart as to how many lamps of a given wattage may be placed on circuits, ie: a 20A circuit may have 44 100W lamps on a 3 wire circuit.
In the estimating section it uses a labor rate of $7.00 per day!
Labor cost for ½” conduit is $0.05 per foot, ceiling outlet $0.15, wall outlet $0.20, S.P. switch $0.25 each and 28 per day.
I'll spend a little time reading and try to post a few interesting items.