The resistor alloy heating element used in power-limiting heating cables has a:

• A. Negative Temperature Coefficient
• B. Positive Temperature Coefficient
• C. Zero Temperature Coefficient
• D. Exponential Temperature Coefficient

Answer: (B)

The heating element in power-limiting cables relies on a material that increases its resistance as it gets hotter. This positive temperature coefficient means that as the element warms, its resistance rises, which reduces the current and automatically lowers the power it dissipates as heat. In a simple view, with a given supply, increasing R reduces P (since P = V^2 / R), so the element self-regulates its temperature and prevents overheating.

If the resistance lowered with temperature (negative temperature coefficient), more current would flow as it got hotter, causing more heat and potential runaway. If the resistance stayed the same regardless of temperature (zero coefficient), there would be no automatic limit on heating. Exponential temperature coefficient isn’t the standard behavior used to describe these elements. Thus the positive temperature coefficient is the characteristic that enables safe, self-limiting operation.