​A4J125 – GOULD 125A 600V FAST ACTING FUSE

The A4J125 uses the Class J rejection-style form factor, so it requires a dedicated Class J fuse holder or fusible disconnect rated for at least 125A and 600V. Class J holders from Bussmann (J series), Littelfuse, and Mersen are all compatible. Standard Class H or K holders will not accept Class J fuses due to the rejection feature — this is by design to prevent under-rated fuse substitution.

The Gould A4J series was transitioned to Mersen (formerly Ferraz Shawmut) following corporate consolidation. The current production equivalent is the Mersen AJT125 (time-delay) or AJBF125 (fast-acting) depending on your application. Northern Breaker Group specialises in obsolete and hard-to-find fuses — contact us and we can source legacy Gould stock or confirm the best current-production cross-reference for your needs.

The 200kA interrupting rating (IR) means the A4J125 can safely clear a fault current of up to 200,000 amperes without rupturing or causing a hazard. This is one of the highest available IR ratings for Class J fuses and makes the A4J125 suitable for use close to the service entrance or in industrial panels with high available fault current. Always verify that your fuse's IR meets or exceeds the available fault current at the point of installation — a fuse with an insufficient IR rating is a serious safety hazard.