The wattage output of series resistance heating cables depends on the total circuit length and:

• A. Voltage
• B. Current
• C. Resistance
• D. Ambient temperature

Answer: (A)

When a resistive heating cable operates, the heat produced is the electrical power dissipated in the cable, given by P = V^2 / R. The total resistance in a series heating cable adds up along its length, so R_total is proportional to the circuit length. This means that, for a fixed supply voltage, increasing the length (and thus R_total) lowers the wattage output, while increasing the voltage raises the wattage output as V^2. So the wattage is determined by the supply voltage and the total circuit length (through resistance). Ambient temperature can affect resistance slightly, but it is not the primary factor setting the wattage. Current is not an independent factor here, since it is determined by V and R (I = V / R).