The procedure for wiring an electric baseboard heater varies according to the capacity of the heater, whether the heater is a 240- or 120-volt model. Generally, it involves connecting the heater to the power breaker, followed by connecting a thermostat to both the breaker and heater.
Shut off the electrical power supply to the baseboard circuit at the main electrical panel, and run a non-metallic sheathed wire from the panel to the location of installation. If the baseboard heater has no built-in junction box, cut in the junction box to allow for feeding in.
To wire a 240-volt baseboard heater, connect the two insulated wires of the heater to a two-pole 20-amp circuit breaker, and connect the bare copper wire to the ground buss. To indicate that the white wire is live, wrap it with a black or red tape before attaching it to the breaker. Next, attach a thermostat by connecting the two top wires of the thermostat to the two breaker hot leads, and connect the two bottom thermostat wires to the heater. Then, attach the bare ground wire to the ground screw.
For a 120-volt baseboard heater, connect the black wire of the heater to a 20-amp breaker, and attach the white and ground wires to the neutral buss and ground buss respectively. Finally, switch on the power, and test the heater.