Industrial Electronic Fuses - Current Limiting Class J

Edison JDL Class J fuses are among the most current limiting time-delay fuses available. Their small physical size and high performance characteristics make Class J fuses ideal for any space-limited application.

Current ratings up to 600 amps on class J current limiting fuses!

A Current-Limiting Fuse meets the following three conditions:

1. Interrupts all available overcurrents within its interrupt rating.
2. Within its current limiting range, limits the clearing time at rated voltage to an interval equal to, or less than, the first major or symmetrical current loop duration.
3. Limits peak let-through current to a value less than the available peak current.

See our catalog to refer to the fuse selection guide, which includes a general summary of the specifications included for each fuse type.

This selection guide does not include the many variables that can exist for specific situations such as local codes, unusual temperature, or other operating conditions.

When selecting fuses, be sure to comply with any applicable PUBLIC SAFETY standards that apply to Overcurrent Protection Devices (OPD).

Dual Element Time-Delay Class J Fuses Overview

Fuse Construction and Operation

The typical fuse consists of an element which is surrounded by a filler and enclosed by the fuse body. The element is welded or soldered to the fuse contacts (blades or ferrules).

The element is a calibrated conductor. Its configuration, mass and the materials employed are selected to achieve the desired electrical and thermal characteristics. The element provides the current path through the fuse. It generates heat at a rate dependent on its resistance and the load current.

The heat generated by the element is absorbed by the filler and passed through the fuse body to the surrounding air. The filler material, such as quartz sand, provides effective heat transfer and allows for the small element cross-section typical in modern fuses. The effective heat transfer allows the fuse to carry harmless overloads. The small element cross section melts quickly under short-circuit conditions. The filler also aids fuse performance by absorbing arc energy when the fuse clears an overload or short circuit.

When a sustained overload occurs, the element will generate heat at a faster rate than the heat can be passed to the filler. If the overload persists, the element will reach its melting point and open. Increasing the applied current will heat the element faster and cause the fuse to open sooner. Thus, fuses have an inverse time current characteristic: that is, the greater the overcurrent, the less time required for the fuse to open the circuit.

This characteristic is desirable because it parallels the characteristics of conductors, motors, transformers, and other electrical apparatus. These components can carry low-level overloads for relatively long periods without damage. However, under high-current conditions, damage can occur quickly. Because of its inverse time current characteristic, a properly applied fuse can provide effective protection over a broad current range, from low-level overloads to high-level short circuits.