TR125R – GOULD 125A 600V CLASS RK5 TIME DELAY FUSE

Both classes share the same physical dimensions and fit Class RK rejection holders, but Class RK1 fuses (like the Bussmann LPN-RK or Littelfuse FLNR) have tighter current-limiting performance. The TR125R is RK5, which provides a broader time-delay and is commonly used for motor branch-circuit protection. You can upgrade from RK5 to RK1 in the same holder for improved current limiting, but you cannot install an RK1 fuse in a holder designed exclusively for RK5 — the rejection feature prevents it. Always verify your holder's class rating before substituting.

The Gould TR series was transitioned when Gould's fuse division became Ferraz Shawmut (now Mersen). The TR125R may be available as new-old-stock or through specialty distributors like Northern Breaker Group. Direct cross-references include the Ferraz Shawmut TR125R (same series), the Bussmann FRN-R-125 (Class RK5, time delay), and the Littelfuse FLNR125 — all are 125A, 600V, Class RK5 time-delay fuses. Contact us and we'll check current stock availability.

Electric motors draw a significant inrush current — typically 6 to 8 times their full-load amperage — during startup. A standard fast-acting fuse would blow under this temporary surge. The TR125R's time-delay feature allows it to withstand these brief inrush currents without nuisance tripping, while still providing fast, reliable protection against sustained overloads and short circuits. This makes Class RK5 time-delay fuses the preferred choice for motor branch-circuit and feeder protection per Canadian Electrical Code (CEC) requirements.