In many cases, the incident energy exposures at equipment of existing fusible systems can be reduced by upgrading which fuses to Class RK1 fuses?

• A. Class RK1 fuses
• B. Class H fuses
• C. Class K5 fuses
• D. Class RK5 fuses

Answer: (A)

Incident energy from an arc flash is largely determined by how long the fault current is allowed to flow before the protective device clears it. Upgrading to Class RK1 fuses reduces that energy exposure because RK1 fuses are built for fast fault clearance in low‑voltage equipment and typically interrupt faults quicker than older or alternative fuse types. That faster clearing shortens the arc duration, which is the main factor driving incident energy. In existing fusible systems, this improves the overall protection by ensuring faults are interrupted promptly and more reliably, reducing the amount of energy released during the fault. The other fuse options listed do not provide the same combination of fast clearing and appropriate coordination for this purpose, so they won’t reduce incident energy as effectively.