...........(note above that there was a mistake in a portion of my second post)
I wouldn't call it a mistake, Pierre. I just think your keyboard doesn't know what your brain does. PEBOAK error (Problem Exists Between Operator And Keyboard). :grin:
To expound on this confusion, using a white wire (technically called
grounded today, but back then it was called the
identified conductor) in single-pole, 3-way and 4-way switch loops was and is still permitted.
Starting in the 1937 NEC, it was expressly stated that using a white wire in switch loops did not require re-identification as a 'hot' wire, but this exception only applied to switch loops. Using a white as a constant hot wire, such as 10-2 feeding an electric water heater, has always required re-identification at all access points in the circuit (panel, at the heater, any LBs or junction boxes, etc.).
Language was also present that required the white to be used to bring power to the switches, and disallowed it from being used to take the switch leg back to the light.
In 1999, the language changed to require re-identification of the white when used in switch loops.
This concludes todays history lesson.