That is how it used to be in North America, prior to about 1950. There was a transition from knob-in-tube wiring to two conductor, then fairly quickly to three conductor where one conductor is the safety ground.
That is how it used to be in North America, prior to about 1950. There was a transition from knob-in-tube wiring to two conductor, then fairly quickly to three conductor where one conductor is the safety ground.