Sounds like it is a 220-240 Volt hot water heater. The black and red are connected to the 220 volts supply and the white is connected to Neutral. At the breaker panel red and black connect to the 2-pole 220 volt breaker and white goes to the neutral bus bar.
If both wires are black then the one with the writing is the neutral wire. If the two wires are black and white then the white one is the neutral.
It is because the nec standard.
If both wires are black, the one that connects to your white wire is the one that should have little writing on it. Black to the plain black wire, white to the wire with writing.
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.
In the heater you will have two wires. You should then have 2 supply wires from the panel, and 2 wires from the thermostat. The neutral (white) supply wire should go to one of the wires on the heater. The hot (black) supply wire should connect to one wire from the thermostat. The other wire from the thermostat will connect to the other wire from the heater.
Connect to two wires you have to the the spade connectors and forget the ground connector. The spade connector wires should be black and white. Black to gold and white to silver. If the wires coming from the heater happen to be red and white, then red goes to black. You could buy a simple lamp cord which has only tow wires.
4 wires, the black ones are the O2 heater (on the sensor side), the white and green are the O2 sensor itself
An electric baseboard heater usually requires a dedicated 240-volt circuit with a double-pole thermostat. The wiring involves connecting the heater to the power supply by matching the colors of the wires (black to black, white to white, and green/bare to ground). It's important to follow the manufacturer's instructions and all applicable electrical codes when installing the heater.
In house wiring, the standard color code for identifying black wires is black, and for white wires is white.
the water heater operates at high power compared to the lights and so the water heater requires a larger current. The wires supplying current to the water heater are thicker so that the wires have a low resistance. This reduces the risk of the wires overheating.
The color of the wires in the electrical circuit are green, black, and white.
The black wires are the heater wires, the white wire is the signal wire and the green is the ground wire.
BLACK WIRES=HEATER CIRCUIT WHITE WIRE=SENSOR GROUND BLUE WIRE=SENSOR PLUS VOLVOKAHUNA.COM
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.
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 correct order for connecting the red, black, and white wires in an electrical circuit is typically red to black to white.