How do you calculate voltage drop in a conductor?

How do you calculate voltage drop in a conductor?

• A. V_drop = P × R of the conductor.
• B. V_drop = I ÷ R of the conductor.
• C. V_drop = V × I for the conductor.
• D. V_drop = I × R of the conductor; compare to allowable drop per specs.

Answer: (D)

Voltage drop comes from the resistance the current has to push through. The relationship is V = I × R, so the drop along a conductor is simply the current times that conductor’s resistance. To calculate it, find the resistance of the length under load (R = ρL/A or use the known resistance per length for the gauge, adjusted for temperature), multiply by the actual current, and you get the voltage drop in volts. Then compare that value to the allowable drop in the specs or code. If it’s too large, you’d use a conductor with lower resistance (larger cross-section or shorter run) or otherwise reduce the drop. Why the other approaches aren’t right: multiplying P by R mixes power with resistance and doesn’t yield voltage; dividing current by resistance gives current divided by resistance, not a voltage; multiplying voltage by current gives power, not drop.

Voltage drop comes from the resistance the current has to push through. The relationship is V = I × R, so the drop along a conductor is simply the current times that conductor’s resistance. To calculate it, find the resistance of the length under load (R = ρL/A or use the known resistance per length for the gauge, adjusted for temperature), multiply by the actual current, and you get the voltage drop in volts. Then compare that value to the allowable drop in the specs or code. If it’s too large, you’d use a conductor with lower resistance (larger cross-section or shorter run) or otherwise reduce the drop.

Why the other approaches aren’t right: multiplying P by R mixes power with resistance and doesn’t yield voltage; dividing current by resistance gives current divided by resistance, not a voltage; multiplying voltage by current gives power, not drop.