Doubling the load on a resistive connection is expected to increase the temperature rise by about how much?

• A. 2X
• B. 3X
• C. 4X
• D. 5X

Answer: (B)

When a resistive connection carries current, heat is produced according to I^2R. If you double the load (increase current), the power dissipated tends to go up a lot—in theory, doubling the current makes the heat generation rise fourfold because the I^2 term grows with the square of the current. However, how hot the connection actually gets depends on how efficiently it can shed that heat to the surroundings. As temperature rises, cooling mechanisms (conduction to the support, convection to air, and even radiation) play a larger role, so the temperature rise does not scale perfectly with the fourfold increase in heat. In practice, the commonly used rule of thumb in electrical thermography is that doubling the load tends to produce about a threefold increase in temperature rise. This is a useful approximation for estimating heating and for identifying abnormal hotspots, though the exact factor can vary with contact resistance, materials, ambient conditions, and airflow.