Electrical Fuses

Fuses are circuit elements that protect devices and users by interrupting the circuit during overcurrent conditions. These components prevent damage to sensitive or expensive components in the circuit by opening the circuit when overcurrent occurs.

Operating Principles

Fuses are designed according to different principles to protect circuits against overcurrent. In fuses operating on the melting wire principle, a wire connected in series with the circuit heats up and reaches its melting point under overcurrent conditions, thereby melting and breaking the circuit. The alloy used in this type of wire determines the fuse’s sensitivity. PTC (Positive Temperature Coefficient) fuses increase their resistance when current rises, thereby interrupting the circuit; when they cool down, they return to a conductive state and restore the circuit. Due to these properties, they are reusable and widely preferred in electronic circuits.

Electronic control fuses monitor current using electronic circuits and automatically interrupt the circuit during overcurrent conditions, making them suitable for sensitive applications. Bimetallic circuit breakers operate based on the differential thermal expansion of two different metals. This difference in expansion mechanically opens and closes the circuit, and such breakers are commonly used in household applications.

History and Development

The fundamental principle of the fuse was developed at the end of the 19th century. As electrical systems became widespread, the need for protective devices increased, and fuses became standard in both residential and industrial applications. With advancing technology, fuse types diversified and were classified according to time-current characteristics, sensitivity, and physical dimensions.

Types of Fuses and Applications

Fuse types are classified according to their operating principles and application areas:

• Tube Glass Fuses: These fuses operate on the melting wire principle and provide fast response, making them commonly used in sensitive electronic devices.
• Blade-Type Fuses: Preferred in automotive applications due to their robust construction and vibration-resistant blade contacts.
• Bolt-on Fuses: Capable of safely interrupting high current levels, these are used in industrial panels due to their performance characteristics.
• NH Fuses: Widely used in industrial facilities, generator outputs, and main distribution panels due to their high breaking capacity based on the melting wire principle. Their metal handle design enables easy and safe insertion and removal.

Standards and Installation Rules

Fuse systems are defined by international standards such as IEC 60269, UL 248, and IEEE 242. These standards specify time-current curves, physical dimensions, performance tolerances, and safety criteria for fuses. According to IEC 60269, “gG” fuses are intended for general use and provide protection against both short circuits and overcurrent. “aM” fuses are used exclusively for short-circuit protection in motor circuits.

Several important considerations must be observed during fuse installation. First, fuse elements must be used within the voltage and current ranges specified in the manufacturer’s catalog. Improper tightening torque can cause loose connections and failures due to excessive thermal stress. Particularly with NH-type fuses, it is critical that the contact surfaces of the fuse disconnectors remain free of oxidation to ensure proper conductivity. Fuses used in conjunction with surge arresters must be selected in accordance with the pairing guidelines specified by the manufacturer. The type of surge arrester (Type 1 or Type 2) directly influences the appropriate fuse selection.