Paul-- Slightly related...the 5+volt several-hundred-amp power supplies on PDPs made sort of a welder, and over here they were rated 208V 3ø.
Ok, here is one of a million possibilities. An early mention of 480Y and 208Y was published in Donald Beeman's 1955 Industrial Power Systems Handbook. I worked in a plant built in 1957 that was Textbook Beeman...almost scary.
I first came across 480Y in small-town baseball field lighting. A state architect had called for Y-service to power about a ¼ megawatt of quartz-halogen lamps that was being built by the local one-man shop, and the janitor who could drive a tractor to set 60-foot wood poles and feed wire to the electrician on the other end. The little irrigation-district utility was flabbergasted when they hooked the “H-frame” bank up in delta, and floored by the 277V ø-ø readings, coupled with the fact that the transformers had only two [not 4] secondary bushings/spades/eyebolt connections, and they still had to sag a fourth lead to the switchboard. I’m sure that the utility’s meterman was foaming at the mouth wondering how in the heck his CTs and meter was ever going to work with this terrible new system. All they had ever done was ∆-∆ for a million irrigation pumps and a few “giant” plants. Wye service started showing up in school plans from the state architect’s office, probably because that was their cookie-cutter/boilerplate way that had worked so far and little rural utilities had to get in line with these “really weird” 120 and 277V “wye” transformer configurations. I think some linemen wanted to get a preacher to absolve this evil thing crammed down their throats by stupid guys in some distant office building.
My guess is that the delta-secondary transformers was so well entranced because of the influx of dual-secondary/split transformers and motors. Every region seems to have a little different take on it. With solidly-grounded 480Y, it was not yet realized that the arcing burndown potential of a sustained arc at roughly the 150-250V level could be sustained until, in some cases, large-city office-building basement switchboards many sections wide could burn until there was no “fuel” left. It took introduction of reliable, field-testable Ground Fault protection in ’71 for 480∆ to drop out of favor, even though Beeman had been warning of its perils since 1955.
As for Canada, there was probably an similar evolution from 600V∆ to 600Y/346V (or 347V?) It seems like they use a fair amount of 208Y/120 like the southland. 600∆-208Y/120V “dry-types” up north—480∆-208Y/120V “dry-types” in the south. A lot of discharge-lighting ballasts are available in 277V and 347V.
For anal retentives:
600/1.73205 = 346.41 ≈ 346
600/1.73000 = 346.82 ≈ 347
