Why are both wires white and black hot at the outlet, light switch and even at light in the ceiling. I replaced the outlets and switches and lights

Question

Why are both wires white and black hot at the outlet, and light switch and even at the light in the ceiling

Answer 1

In the case of a light switch, it is normal if the switch is setup as follows:

[elec ]B=========#==============+
[panel]W--------+ +X---------X+ |        
                | |           | |   
                (~)           [-]
               light         switch

The white wire is carrying power back to the light, and convention dictates there should be a piece of black tape (X) around the white wire to indicate it is a live return.

It's important that the switch must go against the live lead not the neutral.

-- Minor edit to diagram. The wire from the panel usually ends in the ceiling. A new wire runs to the switch, black to black with a nut, and white (switched hot) back to the fixture. # indicates this nut.

Answer 2

In all reality, there is no official distinction of what color wire is for what. However, common convention says the black = hot/powered/charged/incoming, white = neutral/return, green = ground/earth, and red = switched.

When it comes to 3/4 way switches, it's not uncommon to see 2 blacks, 2 whites, or each color as hot. Same for switched outlets or outlets running in parallel. If an inexperienced homeowner did any kind of rework, could also explain it.