The NFPA 70E informational note to Table 130.7(C)(15)(a) lists the typical fault clearing time for insulated case circuit breakers as 'none of the above'.

The NFPA 70E informational note to Table 130.7(C)(15)(a) lists the typical fault clearing time for insulated case circuit breakers as 'none of the above'.

• A. 1 s
• B. 0.5 s
• C. 2 s
• D. None of the above

Answer: (D)

Fault clearing time for protective devices can strongly influence the arc flash energy you’re exposed to, but for insulated-case circuit breakers there isn’t a single, fixed value that applies to all devices. These breakers rely on both thermal and magnetic trip elements, and the exact time to interrupt a fault depends on the specific breaker design, the fault current level, and how the protection scheme is coordinated. Because of that variability, there isn’t a universal number like 1 second, 0.5 second, or 2 seconds that represents all insulated-case breakers. The informational note is signaling that you should not apply a fixed time to ICCBs; instead, you should use the device’s time-current data or manufacturer information to determine the actual clearing time for a given fault scenario. This is important when estimating incident energy and selecting PPE, since the clearing time directly affects the energy released during the arc.

Fault clearing time for protective devices can strongly influence the arc flash energy you’re exposed to, but for insulated-case circuit breakers there isn’t a single, fixed value that applies to all devices. These breakers rely on both thermal and magnetic trip elements, and the exact time to interrupt a fault depends on the specific breaker design, the fault current level, and how the protection scheme is coordinated. Because of that variability, there isn’t a universal number like 1 second, 0.5 second, or 2 seconds that represents all insulated-case breakers. The informational note is signaling that you should not apply a fixed time to ICCBs; instead, you should use the device’s time-current data or manufacturer information to determine the actual clearing time for a given fault scenario. This is important when estimating incident energy and selecting PPE, since the clearing time directly affects the energy released during the arc.