Automotive fuses are a class of fuses used to protect the wiring and electrical equipment for vehicles. They are generally rated for circuits no higher than 32 volts direct current, but some types are rated for 42-volt electrical systems. They are occasionally used in non-automotive electrical products.
Blade fuses (also called spade or plug-in fuses), with a plastic body and two prongs that fit into sockets, are mostly used in automobiles.
Each fuse is printed with the rated current in amperes on the top.
These types of fuses come in six different physical dimensions:
- LP-mini (APS), also known as low-profile mini.Unofficially, the “low-profile mini” fuse is sometimes incorrectly called “Micro” since the term means smaller than mini, but recently fuses using the Micro name have been released.
- Mini (APM / ATM). The mini fuses were developed in the 1990s.
- Regular (APR / ATC / ATO / ATS) blade-type fuses, also known as standard, were developed in 1976 as ATO by Littelfuse for low voltage use in motor vehicles. Bussmann makes the ATC that also complies with the same ISO 8820-3 and SAE J1284 standards.
- Maxi (APX), heavy-duty.
Blade type fuses can be mounted in:
- Fuse blocks (made of porcelain, slate, or other refractory material). Fuseblocks offer a method of mounting several fuses together or large fuses separately .
- In-line fuse holders, with two standards: IEC-publication 257 1968 Amendment no. 2 to this publication dated January 1989 and UL-standard no. 512. They help to save space. An inline fuse is often seen in add-on electrical accessories, where the manufacturer does not know the electrical current limit of the circuit you are going to patch into. This offers sufficient protection for that individual accessory, without regard to any other devices that might share the same circuit.
- Dual slot fuse holders let you turn one fuse slot into two (in some way, similar to a power strip, but for fuses).
- Or fuse clips. Fuseclips can be inserted into a printed circuit board.
|Blade Size||Blade Group||Dimensions L × W × H||Common Ratings (Maximum Current)|
|Micro2||APT, ATR||9.1 × 3.8 × 15.3 mm||5, 7.5, 10, 15, 20, 25, 30|
|Micro3||ATL||14.4 × 4.2 × 18.1 mm||5, 7.5, 10, 15|
|LP-Mini||APS, ATT||10.9 × 3.81 × 8.73 mm||2, 3, 4, 5, 7.5, 10, 15, 20, 25, 30|
|Mini||APM, ATM||10.9 × 3.6 × 16.3 mm||2, 3, 4, 5, 7.5, 10, 15, 20, 25, 30|
|Regular||APR, ATC, ATO, ATS||19.1 × 5.1 × 18.5 mm||0.5, 1, 2, 3, 4, 5, 7.5, 10, 15, 20, 25, 30, 35, 40|
|Maxi||APX||29.2 × 8.5 × 34.3 mm||20, 25, 30, 35, 40, 50, 60, 70, 80, 100, 120|
Where space permits, a miniature circuit breaker is sometimes used to replace a blade-type fuse in the same fuse holder.
Blade fuses use a common coloring scheme for the Micro2, Micro3, low-profile (LP) Mini, Mini, and regular size fuses, and a partial color similarity with the maxi size fuses. The following table shows the commonly available fuses for each size group.
Regular fuses (ATO) rated 0.5 A, 35 A and 40 A are not mentioned in the DIN standards, but are available in some products from Littelfuse, among others.
Bosch type fuses (also known as continental, torpedo, European, or GBC type fuses) are used in old (often European) automobiles. The physical dimension of this type of fuse is 6×25 mm with conical ends. Bosch type fuses usually use the same color-coding for the rated current. The DIN standard is 72581/1.
Lucas type fuses are used in old British-made or assembled automobiles. The physical length of the Lucas ceramic type of fuse is either 1 inch or 1.25 inch, with conical ends. Lucas Glass tube fuses have straight ends. Lucas type fuses usually use the same color-coding for the rated current. Lucas fuses have three ratings; the continuous current they are designed to carry, the instantaneous current at which they will fuse, and the continuous current at which they will also fuse. The figure found on Lucas fuses is the continuous fusing current which is twice the continuous ampere rating that the system should be using; this can be a source of confusion when replacing Lucas fuses with non Lucas fuses. The Lucas 1/4″ diameter glass tube fuse have a different length as compared to the standard US item. The Lucas 1/4″ diameter glass tube fuse is 1 and 5/32″ [≈29.4 mm] long, while the US standard 1/4″ glass tube fuse is 1 and 1/4″ [≈32.0 mm] long. However many Lucas fuse holders permit the longer U.S. version to be installed easily.
|Color||Continuous ampere (=rated current)||Instantaneous fusing ampere||Continuous fusing ampere|
|Red on Yellow||2.5||6||5|
|Red on Green||5||12||10|
|Green on Black||5||12||10|
|Red on Brown||6||14||12|
|Purple on Yellow||25||60||50|
|Yellow on Red||30||75||60|
Glass tube type
North-American built automobiles up to at least 1986 had electrical systems protected by cylindrical glass cartridge fuses rated 32 volts DC and current ratings from 4 amperes to 30 amperes. These are known as “SFE” fuses, as they were designed by the Society of Fuse Engineers to prevent the insertion of a grossly inadequate or unsafe fuse into the vehicle’s fuse panel.
These SFE fuses all have a 1⁄4 inch diameter, and the length varies according to the rating of the fuse.
- A 4 A SFE 4 fuse is 5⁄8 inch long (the same dimension as an AGA fuse of any rating),
- a 6 A SFE 6 fuse is 3⁄4 inch long,
- a 7.5 A SFE 7.5 fuse is 7⁄8 inch long (same as an AGW fuse of any rating),
- a 9 A SFE 9 fuse is 7⁄8 inch long (same as an AGW fuse of any rating),
- a 14 A SFE 14 fuse is 11⁄16 inch long,
- a 20 A SFE 20 fuse is 11⁄4 inch long (same as an AGC fuse of any rating), and
- a 30 A SFE 30 fuse is 17⁄16 inches long.
There are a number of lookalike fuses which can easily be confused with these. In general this type of fuse will have an “AG” label of some kind, which originally stood for “Automobile Glass”. There are at least seven different sizes of fuses with a 1/4 inch diameter. The fuses listed are the most common for the size, which is always a fast-acting fuse:
- 1AG size, type AGA, 1 A to 30 A, 1/4 inch (6.3mm) diameter by 5⁄8 inch (15.9mm) long
- 2AG size, type AGB, 0.177″ (4.5mm) diameter by 0.588″ (14.9mm) long (frequently replaced with 5mm diameter by 15mm long international size fuse (aka 5 x 15mm – now more readily available)
- 3AG size, type AGC, 0.125 A to 50 A, 1/4 inch diameter (6.3mm) by 11⁄4 inch (31.8mm) long
- 4AG size, type AGS, 9⁄32 inch (7.1mm) diameter by 11⁄4 inch (31.8mm) long
- 5AG size, type AGU, 1 A to 60 A, 13⁄32 inch (10.3mm) diameter by 11⁄2 inch (38.1mm) long. Also called “Midget fuses.”
- 7AG size, type AGW, 1 A to 30 A, 1/4 inch diameter (6.3mm) by 7⁄8 inch (22.2mm) long
- 8AG size, type AGX, 1 A to 30 A, 1/4 inch (6.3mm) diameter by 1 inch (25.4mm) long
- 9AG size, type AGY, 50 A, 1/4 inch (6.3mm) diameter by 17⁄16 inch (36.5mm) long
- UK size, type UK, 35 A to 50 A, 1/4 inch (6.3mm) diameter by 11⁄4 inch (31.8mm) long
These and other fuses are still being manufactured for many applications, including for AC circuits and DC uses. Some are time delayed, slow reacting, or have leads for terminals used in circuits without a fuse holder. Many of the fuse dimensions and characteristics are published by the Society of Automotive Engineers as Standard SAE J 554.
Limiter fuses consist of a metal strip from a lock plate,[clarification needed] for currents over 40 amperes. Frequently, these are used in close proximity to starter battery fuse boxes. They are used also in electric vehicles, e.g., in forklift trucks. Because strip fuses require the use of tools for replacement they are therefore legally considered non-serviceable components for end-users.