If fault loop impedance Zs is higher than the maximum allowable for a protective device rating, what is a likely consequence?

• A. The protective device may not trip quickly enough on a fault.
• B. There will be no effect.
• C. The circuit will trip faster.
• D. The insulation will automatically become thicker.

Answer: (A)

When fault loop impedance is higher than what a protective device can handle, the fault current becomes smaller. Protective devices are designed to trip when the current exceeds a certain level within a specified time. If the impedance is too high, the actual fault current may stay below the device’s trip threshold, so the device may not operate quickly enough to clear the fault. This increases the risk of continued energization, overheating, or damage.

The other options don’t fit because a higher Zs does have an effect (it reduces fault current), it doesn’t make the circuit trip faster, and it doesn’t cause insulation to automatically thicken.