ASA Electrical System Practice Test 2025 – Complete Exam Prep Guide

To determine the voltage drop in a No. 18 copper wire carrying 12.5 amperes over a distance of 50 feet, it is essential to apply Ohm's Law and the formula for voltage drop in a conductor.

The resistance of No. 18 copper wire is approximately 6.385 ohms per 1,000 feet. Since the wire length is 50 feet, we first need to calculate the resistance for this specific length. The resistance for 50 feet can be calculated as:

Resistance (R) = (Length in feet / 1,000) x Resistance per 1,000 feet

R = (50 / 1,000) x 6.385 ohms = 0.31925 ohms.

Once we have the resistance, we can use Ohm's Law to calculate the voltage drop. The voltage drop (V_drop) can be expressed as:

V_drop = Current (I) x Resistance (R)

V_drop = 12.5 amperes x 0.31925 ohms = 3.99 volts.

This value can be rounded to approximately 4 volts. Thus, when looking at the choices provided, the selection of 4V as the answer