Which statement best describes Ohm's law and how it is used to size conductors?

• A. P = V × I; used to measure power factor.
• B. V = I × R; used to calculate current for a given load and to check conductor ampacity and voltage drop.
• C. R = V / I; used to set breaker trip curves.
• D. I = V × R; used to compute impedance

Answer: (B)

Ohm’s law shows how voltage, current, and resistance relate: V = I × R. To size conductors you use that relationship to find the current drawn by the load (I = V / R) and then ensure the conductor can carry that current safely (ampacity) while also keeping voltage drop along the run within limits. The current determines how much heat the conductor will generate, and the resistance of the conductor over the run determines how much voltage is lost as electricity flows. So using V = I × R to calculate the current for a given load and to check both ampacity and voltage drop is the practical way to size conductors.