A fuse is really a kind of over current protection device. Made up of a metal wire or strip, it can melt when too much current flows, to interrupt the circuit to which it is connected. In the case of overload the device fails to prevent excessive current so that further damage can be prevented. Fuses limit threat to human life and property damage.
Wiring regulations lay down specifications for maximum current rating for circuits. Automotive fuses are used to protect the wiring and electrical equipment for vehicles. They get rated for circuits that may not be higher than 24 volts direct current but others may be of types rated for 42-volt electrical systems.
Blade fuses have a plastic body with two prongs that fit into sockets that are commonly used in vehicles. Every one of them is printed with a numerical ampere rating. They come in four different physical dimensions, these being low-profile mini (APS), mini (APM / ATM), regular (APR / ATC / ATO) and maxi (APX) heavy-duty.
The APS fuse is also called micro since the term means smaller than mini. Regular blade types are better known as standard fuses and they were developed in 1976 for low-voltages use in motor vehicles. Mini fuses were introduced in the 1990s. Blade type fuses get mounted on blocks, in-line holders or even clips.
Well known manufacturers of automotive fuses include Bosch making torpedo or ATS types. Used mostly in old automobiles, their physical dimension is 6×25 mm with conical ends. Bosch types use same color coding for the rated current and DIN standard is 72581/1 with size of the fuse at 6×25 mm.
Lucas type fuses are also used in old or assembled automobiles and their length is either 1 inch or 1.25 inch with conical ends. They use same color coding for the rated current. Lucas types have three ratings – continuous current they are designed to carry, instantaneous current at which they will go off and continuous current at which they will also melt.
Modern vehicles having electrical systems protected by glass cartridges are rated 32 volts with current ratings from 4 amperes to 30 amperes. Their dimensions and characteristics are standard J554. All of them are 1/4 inch diameter and length varies according to their ratings. A 4 Amp is 5/8 inch, 20 Amp is 1 1/4 inches and 30 amp is 1 7/16 inches.
The Limiter fuse with metal strips on a lock plate is for currents over 40 amperes. Used in close proximity to starter battery boxes, they are used in electric vehicles like forklift trucks. While blown fuses in cars would not signal a major problem in most cases, but if they are blowing a lot it could be an indication of a problem with the electrical system. This does signify you need to check out vehicle maintenance.