What is the maximum time-delay permitted for ground-fault protection to operate on faults of 3,000 A or more?

What is the maximum time-delay permitted for ground-fault protection to operate on faults of 3,000 A or more?

• A. 1 second
• B. 0.5 second
• C. 2 seconds
• D. 3 seconds

Answer: (A)

The key idea is how quickly ground-fault protection must trip when the fault current is very large. For ground-fault protection of equipment, if a fault current of 3,000 A or more occurs, the protection must operate within one second. This keeps the fault cleared quickly enough to limit damage and reduce arc energy, while still allowing the protective device to react reliably. Therefore, the maximum time-delay permitted is one second. Times longer than that would fail to meet the requirement, while shorter times are possible but do not change the maximum allowed.

The key idea is how quickly ground-fault protection must trip when the fault current is very large. For ground-fault protection of equipment, if a fault current of 3,000 A or more occurs, the protection must operate within one second. This keeps the fault cleared quickly enough to limit damage and reduce arc energy, while still allowing the protective device to react reliably. Therefore, the maximum time-delay permitted is one second. Times longer than that would fail to meet the requirement, while shorter times are possible but do not change the maximum allowed.