FUSE

 

Fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial device; once a fuse has operated it is an open circuit, it must be replaced or rewired, depending on the type.

Fuses have been used as essential safety devices from the early days of electrical engineering. Today there are thousands of different fuse designs that have specific current and voltage ratings, breaking capacity, and response times, depending on the application. The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Wiring regulations usually define a maximum fuse current rating for particular circuits. Short circuits, overloading, mismatched loads, or device failure are the prime or some of the reasons for fuse operation.

A fuse is an automatic means of removing power from a faulty system; often abbreviated to ADS (Automatic Disconnection of Supply). Circuit breakers can be used as an alternative to fuses, but have significantly different characteristics.

fuses may have significantly different properties, identified by their markings. Fuse markings will generally convey the following information, either explicitly as text, or else implicit with the approval agency marking for a particular type:

• Current rating of the fuse.
• Voltage rating of the fuse.
• Time-current characteristic; i.e. fuse speed.
• Approvals by national and international standards agencies.
• Manufacturer/part number/series.
• Interrupting rating (Breaking capacity)

Maximum threshold ratio for various types of fuses:

Fuse Class	Ratio
CLASS RK5	65
CLASS RK1	30
CLASS J	30
CLASS CC	30
CLASS L	30 (601-1200 Amps)
CLASS L	35(1201-2000 Amps)
CLASS L	40 (2001-4000 Amps)