What minimum size THW branch circuit conductors are required for a 240-volt, 4-kilowatt electric baseboard heater?

To determine the minimum size THW branch circuit conductors required for a 240-volt, 4-kilowatt electric baseboard heater, we must first calculate the current (in amperes) that the heater will draw. The power formula used is:

Power (P) = Voltage (V) x Current (I).

Rearranging this gives us:

Current (I) = Power (P) / Voltage (V).

In this scenario, the heater consumes 4 kilowatts (which is equal to 4000 watts) at 240 volts. Plugging in these values results in:

I = 4000 W / 240 V = 16.67 A.

According to the National Electrical Code (NEC), conductors must be sized based on the current-carrying capacity (ampacity) for safe operation. For most applications, it is a standard practice to use a conductor size that supports a 125% application.

Calculating 125% of 16.67 A gives us:

16.67 A x 1.25 = 20.84 A.

Now we can refer to the NEC ampacity charts for THW conductors, which indicate that a 10 AWG conductor can safely handle