Which three factors affect power losses in cables due to conductor resistance heating?

Which three factors affect power losses in cables due to conductor resistance heating?

• A. Cable length; Conductor cross sectional area; The load current connected to the cable
• B. Cable color; Insulation thickness; Ambient temperature
• C. Installation method; Shield material; Cable age
• D. Conductor material; Ground resistance; Ambient humidity

Answer: (A)

The main idea is resistive heating in a conductor follows I^2R losses, so heat generated depends on how much current flows and how much resistance the conductor has. The three factors that directly set that resistance are the cable length (more length means more resistance), the conductor’s cross-sectional area (larger area lowers resistance), and the load current (more current increases losses) — and together they give P = I^2R with R = ρL/A, so P = I^2 ρL/A. That’s why longer cables heat more, bigger cross-sections heat less, and higher current heats more, often quite a bit because the current enters the square term. Other listed factors don’t directly determine conductor resistance heating: things like color, insulation thickness, or age can affect insulation, mechanical aspects, or heat dissipation, but they don’t change the fundamental I^2R loss governed by length, area, and current.

The main idea is resistive heating in a conductor follows I^2R losses, so heat generated depends on how much current flows and how much resistance the conductor has. The three factors that directly set that resistance are the cable length (more length means more resistance), the conductor’s cross-sectional area (larger area lowers resistance), and the load current (more current increases losses) — and together they give P = I^2R with R = ρL/A, so P = I^2 ρL/A. That’s why longer cables heat more, bigger cross-sections heat less, and higher current heats more, often quite a bit because the current enters the square term.

Other listed factors don’t directly determine conductor resistance heating: things like color, insulation thickness, or age can affect insulation, mechanical aspects, or heat dissipation, but they don’t change the fundamental I^2R loss governed by length, area, and current.