High speed fuses

Examples of equipment that may contain semiconductors are soft starters, power converters, adjustable frequency drives, voltage converters, UPS systems, power supplies and solid state relays.

High speed fuses are manufactured in different types depending on the electrical properties, the installation method and local standards. Common types are cylindrical fuses, square body fuses and BS88 fuses.

Fuse selection

The following information are required to choose the right fuse to protect semiconductor devices:

• Rated voltage of the fuse (Un) must be equal or larger than the nominal voltage of the circuit
• Max current (I) in the circuit during normal conditions
• The energy (I²t) cleared by the fuse during a short circuit must be less or equal to the withstand energy of the semiconductor
• The breaking capacity of the fuse must be higher than the prospective circuit short circuit current
• The fuse max permissible load current must be greater than max current during normal operation
• Current/voltage peaks, cyclic loads, temporary overloads etc. do also affect the fuse selection

Power losses

High speed fuses generate higher power losses compared to fuses for cable, line and motor protection. This must be taken into consideration when the fuses are installed in fuseholders or in fuse disconnect switches.

Operating class aR, gR and gS

Traditionally high speed fuses have only been used for short circuit protection, another device in the circuit protects against overload. Fuses only intended for short circuit protection are called operating class aR. Recent technological developments have made it possible to combine both short circuit protection and overload protection into the same fuse, class gR.

Operating class gR and gS offer additional protection compared to class aR. Class gR/gS fuses can often direct replace class aR fuses, however a class gR/gS fuse shall never be replaced by a class aR.

DC applications

We offer a wide range of fuses especially designed for DC applications. To be able to choose correct fuse the time constant (L/R) in ms is also vital.

We help you to select the proper fuse for your application, contact us!