Electrical Inspection, Testing and Certification Practice Exam

What happens to the insulation resistance reading when a number of circuits are added during an IR test?

1. The reading will increase

2. The reading will remain constant

3. The reading will decrease

4. The reading will fluctuate

The correct answer is: The reading will decrease

When conducting an insulation resistance test, adding circuits typically leads to a decrease in the insulation resistance reading. This is because each additional circuit introduces its own resistance and potential leakage paths. In ideal circumstances, insulation resistance is measured in ohms and reflects how much current can leak through the insulation of conductors. When multiple circuits are involved, the overall surface area of insulation being tested increases, and because they may be interconnected or closer together, the risk of capacitance and leakage increases. As a result, the total insulating resistance decreases, yielding a lower reading on the test instrument. Understanding that a decrease in the insulation resistance reading indicates either compromised insulation or a higher potential for leakage paths provides critical insight for electrical inspectors. This decrease serves as an important cue that further investigation or remediation is needed to ensure system safety and reliability.