Bayonet Fuse

The current sensing Bayonet fuse link is used to protect distribution apparatus from damaging currents and to protect distribution systems from failed apparatus. They are used on single-phase conventional and self-protected distribution transformers and other apparatus rated through 500 kVA, and on three-phase equipment through 1500 kVA.

A bayonet fuse is ideal for use in a two-fuse protection scheme with a current-limiting backup fuse. In this arrangement, secondary faults and overload currents are cleared by the bayonet fuse, and high level faults are cleared by the current-limiting fuse. The two fuses are connected in series, and are coordinated so that the current-limiting fuse operates only upon internal equipment failure. If the bayonet fuse will not be used in series with a current-limiting fuse, an isolation link is required.

Bayonet fuses are comparable in cost to internal cartridge fuses but have the advantages of being field-replaceable. They can easily be coordinated with upstream devices.


  • Silver plated brass contacts provide reliable positive current interchange
  • Teflon tube provides track-free bore to withstand full-rated voltage after fuse operation
  • Corrosion-resistant element provides reliable fuse operation


  • Bayonet fuse assemblies
  • Power transformers
  • Distribution equipment


  • Bayonet Fuse Links - Three types of fuse elements are available; a Fault Sensing fuse, Dual Sensing fuse, and Dual Element. The Fault Sensing fuse is sensitive to current only and offers protection to the primary circuit from transformer faults. The Dual Sensing fuse is sensitive to both current and oil temperature, thus providing both secondary protection and transformer protection. The Dual Element combines the two.
  • Isolation Link - All transformers equipped with a bayonet fuse should also be equipped with an isolation link, as a safety feature. The isolation link is connected in series with the fuse and its purpose is to minimize the possibility of an operator closing in on a fault that is beyond the rated interrupting capability of the fuse element. Proper coordination between the isolation link and the fuse element is required.


  • Cooper Power Systems
  • Ermco

Data Sheet:

  • Data Sheet 6: Bayonet Fuse