ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades History of Mains Voltages

More about Norway: If we look really long back the arc lamps around 1920 used DC around 80V, Some houses got 100-120V DC from private generators/batteries. Then we got AC mainly 220V, some areas had 127 for lightning usually 50 Hz but I have heard about a small area with 45Hz, and Svalbard had 25Hz. The trams used 500V DC, later mainly 750V. Trains use 18kV at 16.6667Hz

Its interesting history for sure, the 60hz part i'd say came later,
I think NYC was Edison teritory 100-110V DC, last DC grid shutdown in 2007 there.
Southern California was 110V 50hz until ~1948 (they had to rebuild clocks for free) some parts of SF had 110V DC also.
and Ohio - Pennsylvania - Philadelphia were Westinghouse / Stanley-Tesla 230/115 5 wire two phase at 25 or 60 hz, with a 4kv 3-wire two phase primary some of that exists to this day.
I have read about a old 550V two-phase 3-wire system used in Pittsfield MA that was in use until the possibly the late 1990's.
I believe there are trains on the east coast that still use the 12.5kv 25 hz system, there is no more utility DC, 50hz or 25hz in the west coast of the US that I know of other than HV DC lines from Oregon to LA.
By the 1920's i'd say three phase was standard most places, but it might have been 240/120 hi-leg delta. Later 208/120 wye.
Mexico has converted from 208/120 to 220/127 over the last few decades.

Center tapped delta (Hi Leg) usually seems to be in smaller light industry places and the PoCo does it to save a transformer. 3P wye needs 3 but they can do center tapped "Delta:" actually called "Delta Vee" with 2 transformers. Typically one will be a larger size. If you see this, it is Delta V and the B phase is 208v. A to C is 240 with a center tap.