SM Power Fuses, Outdoor Distribution

Fault Interruption

Fast, positive fault interruption is achieved in SM Refill Units through high-speed elongation of the arc in the solid-material-lined bore, and by the efficient deionizing action of gases generated through thermal reaction of the solid material due to the heat of the confined arc.

Here’s How it Works

1. Overcurrent melts the silver fusible element. The strain wire severs, initiating arcing.
2. Both main and auxiliary arcing rods are drawn upward by spring-and-cable assembly in the holder. After approximately 1/8-inch travel, lower section of the auxiliary arcing rod engages auxiliary contact, momentarily shorting out the arc.
3. For low-magnitude faults, arcing is reinitiated in small-diameter auxiliary bore when the tip of the auxiliary arcing rod travels about one inch (and clears auxiliary contact).
   
   For moderate-to-high-faults, auxiliary arcing rod — momentarily providing the only path for the fault current — quickly melts at reduced section and separates from the one-inch long arcing tip. Any arcing in the auxiliary bore can't persist, and quickly transfers to main arcing rod in the main bore.
4. For low-magnitude faults, large-diameter section of auxiliary bore delays arc extinction until a sufficient gap is attained to preclude reignition in the main bore.
   
   For moderate-to-high faults, arc is lengthened as the main rod is drawn upward into the main bore. The large circumference of main bore provides greater surface exposure of the arc-extinguishing medium to the heating effects of the arc, thereby enhancing generation of arc-quenching deionizing gases.
5. For low-magnitude faults, after auxiliary arcing rod has traveled about one-half stroke, sufficient deionization has occurred to extinguish the arc.
   
   For moderate-to-high faults, after main arcing rod has traveled about one-half stroke, sufficient deionization had occurred to extinguish the arc.