A4J300 – GOULD 300A 600V FAST ACTING FUSE

The A4J300 is a Class J fuse and requires a Class J fuse holder or fused disconnect rated for at least 300A and 600V. Class J holders use a specific knife-blade configuration that prevents incorrect installation of lower-class fuses, so ensure your holder is explicitly rated for Class J.

The A4J300 is a fast-acting (non-time-delay) Class J fuse. It responds very quickly to both overloads and short circuits, making it ideal for protecting equipment that has no high inrush current on start-up — such as capacitors, transformers, and sensitive electronic or semiconductor equipment. For motors or other loads with high inrush, a time-delay Class J fuse (such as the AJT or LPJ series) is typically recommended instead. If you're unsure which type suits your application, our specialists are happy to help.

Gould's fuse product line was acquired by Ferraz Shawmut, which is now operating as Mersen. The A4J series has direct modern equivalents — the Mersen AJT300 (time-delay) and AJ300 (fast-acting) are the primary successors, and Bussmann's LPJ-300SP is a common cross-reference. Northern Breaker Group specialises in obsolete and hard-to-find electrical components; contact us for current stock of the original Gould A4J300 or a confirmed equivalent for your application.