Electrical Inspection, Testing and Certification Practice Exam

To find the value of R1 + R2, one should utilize the formula that relates Zs (service impedance), Ze (earth electrode impedance), and the resistances of the circuit (R1 and R2). According to the principles of electrical testing and safety, the overall service impedance Zs is equal to the sum of the earth fault loop impedance Ze and the combined resistances of R1 and R2.

The formula can be expressed as:

Zs = Ze + (R1 + R2)

Given that Zs is 2 ohms and Ze is 1.5 ohms, we can rearrange the equation to solve for R1 + R2:

R1 + R2 = Zs - Ze

R1 + R2 = 2 ohms - 1.5 ohms

R1 + R2 = 0.5 ohms

This calculation clearly shows that the total resistance R1 + R2 equals 0.5 ohms, which corresponds to the first choice listed. This answer reflects the key understanding of how service impedance is calculated in electrical systems, emphasizing the interaction between the various resistances involved.