Everything you wanted to know about automotive fuses

A fuse is really a kind of overcurrent protection device. Composed of a metal wire or strip, it can melt when too much current flows, interrupting the circuit to which it is connected. In case of overload, the device does not prevent excessive current to avoid further damage. Fuses limit the threat to human life and property damage.

Wiring regulations establish specifications for the maximum current rating for circuits. Automotive fuses are used to protect wiring and electrical equipment in vehicles. They are rated for circuits that cannot exceed 24 volts DC, 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 commonly used in vehicles. Each of them is printed with a numerical amp rating. They come in four different physical dimensions, which are mini low profile (APS), mini (APM / ATM), regular (APR / ATC / ATO), and maxi (APX) heavy duty.

The APS fuse is also called a micro, as the term means smaller than mini. The regular blade types are better known as standard fuses and were developed in 1976 for low voltage use in motor vehicles. Mini fuses were introduced in the 1990s. Blade-type fuses mount in blocks, in-line holders, or even clips.

Well known manufacturers of automotive fuses include Bosch which makes torpedoes or ATS types. Mainly used in vintage cars, its physical dimension is 6x25mm with tapered ends. Bosch types use the same color code for rated current and the DIN standard is 72581/1 with a 6x25mm fuse size.

Lucas type fuses are also used in old or assembled cars and their length is 1 inch or 1.25 inches with tapered ends. They use the same color coding for the rated current. Lucas types have three classifications: direct current that they are designed to carry, instantaneous current at which they will turn off, and direct current at which they will also melt.

Modern vehicles that have electrical systems protected by glass cartridges are rated at 32 volts with current ratings from 4 amps to 30 amps. Its dimensions and characteristics are standard J554. They all have a diameter of 1/4-inch and the length varies depending on their qualifications. A 4 amp is 5/8 inches, 20 amps is 1 1/4 inches, and 30 amps is 1 7/16 inches.

The limiting fuse with metal strips on a lock plate is for currents greater than 40 amps. Used in close proximity to starter battery boxes, they are used in electric vehicles such as forklifts. While blown fuses in cars won’t indicate a major problem in most cases, if they blow badly, it could be an indication of a problem with the electrical system. This means that you should check the maintenance of the vehicle.