It is because the nec standard.
If this is a home wiring question and the wires are black and white then black is Hot and white is Neutral. If you also have a red wire, it is the other hot wire, and either the black or the red wire to the white one would be 120 volts, and red to black would be 240 volts.
Assuming the wires are the correct gauge for application and breaker you use black and white wires as hot. Put red electrical tape on each end of white wire and connect red and black to the breaker output and bare wire to ground lug in panel. At receptacle connect black and red to hot contacts and bare wire to ground lug.
Load (or hot wire, usually black or red), Neutral, (white), and ground,(green) wire.
On a 3 wire dryer cord there is no green wire. The white wire coming from the outlet is connected to ground or the green screw. The black and red wires are the hot wires.
You will have to run new electrical wire or a single ground wire back to the panel (though the former is highly recommended). A GFCI outlet will cut off the circuit if it senses voltage leaking to ground. If there is no ground wire, it will not function.
In an electrical circuit, both the black and white wires can be considered hot depending on the wiring configuration.
hot wires are black, white wires are ground
The difference between white and black wires in electrical circuits is that white wires are typically used as neutral wires, while black wires are usually used as hot wires. Neutral wires carry current back to the power source, while hot wires carry current from the power source to the device being powered.
If this is a home wiring question and the wires are black and white then black is Hot and white is Neutral. If you also have a red wire, it is the other hot wire, and either the black or the red wire to the white one would be 120 volts, and red to black would be 240 volts.
The standard color code for home wiring is black for hot wires and white for neutral wires.
The standard color coding for electrical wires in a circuit is red for live or hot wires, black for neutral wires, and white for ground wires.
The different colors of wires used in electrical installations have specific meanings. Red wires are typically used for hot wires, white wires for neutral wires, green wires for ground wires, and black wires for hot wires as well.
The standard color codes for house wiring are black for hot wires and white for neutral wires.
In electrical circuits, white wires are typically used as neutral wires, green wires are used as ground wires, and black wires are commonly used as hot wires.
Common wire colors found in old house wiring include black, white, and red. Black wires are typically used for hot wires, white wires for neutral wires, and red wires for secondary hot wires or switch legs.
The standard color coding for electrical wires is green for ground, black for hot, and white for neutral.
In a typical household wiring system, the standard color coding for electrical wires is white for neutral wires and black for hot wires.