Fuse (electrical)
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In electronics and electrical engineering a fuse (short for fusible link) is a type of overcurrent protection device. Its typical component is a metal wire or strip (element) that melts when too much current flows, which interrupts (disconnects) the circuit in which it is connected. Circuit or device failure is often a reason for excessive current. A fuse blows (interrupts excessive current) so that further damage (ie. fire) is prevented. A fuse typically is not intended to protect from the initial cause of overcurrent.
Overcurrent protection devices are an essential part of appliances and of power distribution systems to limit both threats to human life and damage. For example, too much current for too long may cause a wire to overheat, be damaged, or even start a fire. Wiring regulations often define a maximum fuse current rating. Fuses are selected to allow passage of normal current and of excessive current for short periods. And to interrupt what is called a short circuit, overload condition, or fault current.
A fuse was patented by Thomas Edison in 1890 [1] as part of his successful electric distribution system. Edison writes, "The passage of an abnormal electric current fuses the safety-catch and breaks the circuit, as will be understood."
[edit] Characteristic parameters
Rated current IN A maximum current that the fuse can continuously conduct without interruption to the circuit, or harmful effects on its surroundings. A fuse is derated 25% when selected. For example a 10 amp fuse is typically used for loads of up to 7.5 amps.
Speed The speed at which a fuse blows depends on how much current flows through it and the material of which the fuse is made.
Fuses are often characterized as "fast-blow", "slow-blow" or "time-delay", according to time required to respond to an overcurrent condition. Fuse selection depends on the load's characteristics. Details provided in I2t charts in manufacturer datasheets.
Semiconductor devices may use a fast or ultrafast fuse since circuit board conductors may have little capacity to withstand the resulting overcurrent after a semiconductor fails. Fuses applied on motor circuits may have a time-delay characteristic, since the initial current surge during startup soon decreases and is harmless to wiring and the motor and protect the circuit.
The I2t value A measure of energy required to blow the fuse element relates actual current to time that a fuse actually blows (clears or disconnects). For example, 1.5 amps through a one amp fuse may take 45 seconds. Same fuse may blow after 3 amps for 2 seconds or 6 amps for 100 milliseconds. That same 1 amp fuse might conduct 2 amps for 2 seconds and remain conductive.
These characteristics vary for each fuse family. Ballpark numbers suggests a standard fuse may require twice its rated current to open in one second. A fast-blow fuse may require twice its rated current to blow in 0.1 seconds. And a slow-blow fuse may require twice its rated current for tens of seconds to blow. Unique I2t parameters are provided by charts in manufacturer datasheets for each fuse family.
Voltage drop A voltage drop across the fuse is usually provided by its manufacturer. Resistance may change when a fuse becomes hot due to energy dissipation while conducting higher currents. This resulting voltage drop should be taken into account particularly when using a fuse in low-voltage applications. Voltage drop often is not significant in more traditional wire type fuses. But can be significant in other technologies such as resettable fuse (PPTC) type fuses.
Breaking capacity The breaking capacity is a maximum current that can safely be interrupted by the fuse. Generally this should be higher than the prospective short circuit current. Miniature fuses may have an interrupting rating only 10 times their rated current. Some fuses are designated High Rupture Capacity (HRC) and are usually filled with sand or a similar material. Fuses for small low-voltage (ie residential) wiring systems are commonly rated to interrupt 10 000 amperes. Fuses for larger power systems must have higher interrupting ratings, with some low-voltage current-limiting HRC fuses rated for 300,000 amperes. Fuses for high-voltage equipment, up to 115 000 volts, are rated by the total apparent power (megavolt-amperes, MVA) of the fault level on the circuit.
Rated voltage Voltage rating of the fuse must be greater than or equal to what would become the open circuit voltage. For example, a glass tube fuse rated at 32 volts (a 0.25" inch diameter by 1.25" inch fuse typically found in older automobiles) would not reliably interrupt current from a voltage source of 120 or 230 V. Fuses carrying a 250 V rating may be safely used in a 125 V circuit. If a 32 V fuse attempts to interrupt the 120 or 230 V source, an arc may result. Plasma inside that glass tube fuse may continue to conduct current until current eventually so diminishes that plasma reverts to an insulating gas. Rated voltage should be larger than the maximum voltage source it would have to disconnect. This requirement applies to every type of fuse.
Rated voltage remains same for any one fuse even when similar fuses are connected in series. Connecting fuses in series does not increase a resulting rated voltage.
Medium-voltage fuses rated for a few thousand volts are never used on low voltage circuits, due to their expense and because they cannot properly clear the circuit when operating at very low voltages.
Temperature Rerating Ambient temperature will change a fuse's operational parameters. A fuse rated for 1 amp at 25°C may conduct up to 10% or 20% more current at -40°C and may open at 80% of its rated value at 100°C. Of course, operating values will vary with each fuse family and are provided in manufacturer datasheets.
[edit] Markings
Most fuses are marked on the body or end caps with markings that indicate their ratings. Surface mount technology "chip type" fuses feature few or no markings, making identification very difficult.
When replacing a fuse, it is important to interpret these markings correctly as fuses that may look the same could be designed for very different applications. Fuse markings[2] will generally convey the following information;
- Ampere rating of the fuse
- Voltage rating of the fuse
- Time-current characteristic ie. element speed
- Approvals
- Manufacturer / Part Number / Series
- Breaking capacity
[edit] Approvals
The majority of fuse manufacturers build products that comply with a set of guidelines and standards, based upon the application of the fuse. These requirements are devised by many different Government agencies and certification authorities. Once a fuse has been tested and proven to meet the required standard, it may then carry the approval marking of the certifying agency.
[edit] UK domestic fuses and their markings
There are generally two sizes of modern domestic fuse found in the UK. The first is the standard plug top fuse which is ¼" inch diameter by 1" long (Ø 6.3 x 25.4 mm). The second is a smaller fuse which is generally found inside modern electrical equipment and is 20 mm long and 5 mm in diameter.
The performance of both types of fuse is governed by the characteristic parameters (mentioned above), which can be identified from the markings on the side of the fuse.
Speed The first marked parameter is the speed with which the fuse blows. The fastest blowing fuses are designated "FF" (or flipping fast!), these are designed for the most sensitive electrical equipment where even a short exposure to an overload current could be very damaging. Next on the scale are normal fast blow fuses designated simply "F", these are the most general purpose fuses and are very widely used in applications where the ultra fast blow speed of "FF" fuses is not required. The next type of blow speed is the time delay fuse (also known as anti-surge, or slow-blow), designated "T". Time delay fuses are designed to allow a current which is above the rated value of the fuse to flow for a short period of time without the fuse blowing. These types of fuse are used on equipment which draw a large initial current for a few milliseconds after they have been switched on.
Rated current The second marked parameter is the rated current of the fuse. This is simply the maximum current that will be allowed to flow through the fuse before it blows. This will be written in either Amps (A) or milliamps (mA) on the side of the fuse.
Breaking capacity The third marked parameter is the breaking capacity, or the potential maximum current the fuse can withstand without shattering. There are two types of fuse in this case, High Blow Current (HBC) and Low Blow Current (LBC). HBC fuses (sometimes known as HRC or High Rupture Current) are generally defined as being able to withstand more than 10 times their rated current without shattering. They typically have a ceramic body and are filled with sand. UK plug fuses are HBC fuses. HBC fuses are designated "H". LBC fuses on the other hand are designed for situations where the maximum fault current is likely to be less than 10 times the rated fuse current. They typically have a glass body in which the fuse wire can clearly be seen, making it very easy to see if the fuse has blown. LBC fuses are designated "L".
Rated voltage The fourth marked parameter is the rated voltage of the fuse. In the UK domestic fuse, this will generally be 240/250V.
These attributes are marked on the side of the fuse, in the order presented here. So for example a fuse which has "F500mAL250V" written on the side is a fast blow fuse rated to 500 milliamps and is an LBC fuse designed for circuits with a smaller maximum fault current and running at 250 Volts, and a fuse with "T5AH250V" written on the side is a time delay fuse rated to 5 Amps and is HBC and rated to 250 Volts.
[edit] Packages
Fuses come in a vast array of sizes & styles to cater for the immense number of applications in which they are used. While many are manufactured in standardised package layouts to make them easily interchangeable, a large number of new styles are released into the marketplace every year. Fuse bodies may be made of ceramic, glass, plastic, fiberglass, Molded Mica Laminates, or molded compressed fibre depending on application and voltage class.
Cartridge (ferrule) fuses have a cylindrical body terminated with metal end caps. Some cartridge fuses are manufactured with end caps of different sizes to prevent accidental insertion of the wrong fuse rating in a holder. An example of such a fuse range is the 'bottle fuse', which in appearance resembles the shape of a bottle.
Fuses designed for soldering to a printed circuit board have radial or axial wire leads. Surface mount fuses have solder pads instead of leads.
Fuses used in circuits rated 200-600 volts and between about 10 and several thousand amperes, as used for industrial applications such as protection of electric motors, commonly have metal blades located on each end of the fuse. Fuses may be held by a spring loaded clip or the blades may be held by screws. Blade type fuses often require the use of a special purpose extractor tool to remove them from the fuse holder.
Semi-enclosed fuses are fuse wire carriers in which the fusible wire itself can be replaced. These are used in consumer units in some parts of the world, but are becoming less common.
[edit] Materials
While glass fuses have the advantage of a fuse element visible for inspection purposes, they have a low breaking capacity which generally restricts them to applications of 15 A or less at 250 VAC. Ceramic fuses have the advantage of a higher breaking capacity facilitating their use in higher voltage/ampere circuits. Filling a fuse body with sand provides additional protection against arcing in an overcurrent situation.
[edit] Dimensions
Cartridge fuses are generally measured as the overall length and diameter of the fuse. Due to the large variety of cartridge fuses available, fuse identification relies on accurate measurements as fuses can differ by only a few millimeters between types. 'Bottle style' cartridge fuses also require the measurement of the cap diameter as this varies between ampere ratings.
Other fuse packages can require a variety of measurements such as;
- Body (width x height x depth)
- Blade or tag (width x height x depth)
- Overall length of the fuse (when the fuse features blades or tags)
- Overall width of the fuse (when the fuse features 2 bodies)
- Width of the mounting holes (when the fuse features tags)
- Distance between blades (when radially configured)
- Fixing centre (when the fuse features tags - see below)
Fuses fitted with tags require the fixing centre measurement. This measurement is the distance between the tag mounting holes on either end of the fuse as measured from the centre of each mounting hole.
[edit] Special features
Glass cartridge and plug fuses allow direct inspection of the fusible element. Other fuses have other indication methods including:
- Indicating pin or striker pin: extends out of the fuse cap when the element is blown.
- Indicating disc: a coloured disc (flush mounted in the end cap of the fuse) falls out when the element is blown.
- Element window: a small window built into the fuse body to provide visual indication of a blown element.
- External trip indicator: similar function to striker pin, but can be externally attached (using clips) to a compatible fuse.
- Some fuses allow a special purpose microswitch or relay unit to be fixed to the fuse body. When the fuse element blows, the indicating pin extends to activate the micro switch or relay which in turn triggers an event.
[edit] Standard designs
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[edit] D Type fuses for residential and commercial installations
D-type (Diazed) fuse cartidges have a bottle-shaped ceramic body with metal end caps, and are fitted in screw-in fuse holders. They are available 5 different body sizes, with ratings from 2A up to 200A (see table).
D0-type (Neozed) fuses are similar, but have a more compact, cylindrical body. They are available in 3 different sizes with ratings from 2A up to 100A (see table).
The fuse cartridges can be replaced by unskilled personnel, if the rated current and voltage does not exceed 63 A / 400 V AC. And are therefore suitable for use in residential installations. In some jurisdictions, replacement of the fuse cartridge by unskilled personnel is allowed only for fuses up to a certain maximum rating.
The smaller end cap (the "top" of the bottle, but usually called the "foot contact") has a diameter that varies with the fuse rating: higher ratings have wider end caps. The fixed part of the fuse holder contains a (usually color coded) gauge ring, which will accept end caps up to a certain diameter. It is therefore not possible to fit a fuse of a higher rating than allowed for by the gauge ring. The size of the gauge ring is determined by the current rating of the circuit to be protected. Gauge rings can be changed only by authorized personnel.
The larger end cap (the "bottom" of the bottle) has at its center a small spring loaded button retained by a thin wire, which serves as a "fuse blown" indicator. When the fuse blows, the wire breaks and the indicator button is ejected by the spring. A missing or displaced indicator thus pinpoints a blown fuse. The removeable part of the fuse holder has a small window to allow inspection of the indicator without removal of the fuse and to prevent fire risk of any hot metal parts. The indicator button usually has a colored dot indicating the fuse rating (see table).
D- and D0-type fuses are currently used for protection of low voltage (up to 500V AC) circuits in residential and commercial installations, and occasionally for the protection of electric motors. The most common operating class is gG (general purpose, formerly gL), but other classes are available. A gG class fuse will typically blow within 2-5 seconds at 5 times rated current, and within 0.1-0.2 seconds at 10 times rated current.
| 2 A | 4 A | 6 A | 10 A | 13 A | 16 A | 20 A | 25 A |
|---|---|---|---|---|---|---|---|
| Pink | Brown | Green | Red | Black | Grey | Blue | Yellow |
| 32 A | 35 A | 40 A | 50 A | 63 A | 80 A | 100 A | |
| Black | Black | Black | White | Copper | Silver | Red |
Only Diazed data processing (D-system size 5)
| 125 A | 160 A | 200 A |
|---|---|---|
| Yellow | Copper | Blue |
As rule of thumb for fuses in the "gG" operating class (in older times the "gL" standard). A 5-times overload of the designed current shall cause the fuse to break the circuit within 5 seconds. A 10-times overload of the designed current shall cause the fuse to break the circuit within 0.2 seconds. Screw-fuses are manufactured in two different designs:
[edit] D-system (DIAZED)
Fuses of the DIAZED design (Diametrically abgestuftes (graded) z weiteiliges (two-part) Edison gewinde (Edison-thread), from there DiazEd) is actually divided into five sizes. The designation of a size consists of the letter D and a Roman number. There are special types with increased separation distances for voltages up to 750 V; due to their application they are of a substantially longer design and easily differentiated from the standard types.
One danger with the DiaZed type fuses is that you must put the fuse inside the screw thread-holder before inserting them together into the socket. Inserting just the fuse may lead to a dangerous electric shock. This applies to the NEOZED type of fuses as well.
| Size | Designated current | Thread* |
|---|---|---|
| D I | 2 A, 4 A, 6 A, 10 A, 16 A | E 16 |
| D II | 2 A, 4 A, 6 A, 10 A, 13 A, 16 A, 20 A, 25 A | E 27 |
| D III | 35 A, 40 A, 50 A, 63 A | E 33 |
| D IV | 80 A, 100 A | E 44 |
| D V | 125 A, 160 A, 200 A | E 57 |
- E stands for Edison-thread. The sizes D IV and D V are rarely used. D III and D IV are nowadays only used in junction boxes in older houses.
[edit] D0-System (NEOZED)
Fuses of the D0 system (speak D zero) or NEOZED is a smaller implementation than the DIAZED fuses and warms itself up with nominal load more strongly, since the heat discharge is more unfavorable due to the smaller surface. Thus damage and burns on the fuse block can occour. NEOZED fuses are divided into three sizes. The designation of a size builds itself out D0 up and a further Arabic numeral:
| Size | Rated current | Gewinde |
|---|---|---|
| D01 | 2 A, 4 A, 6 A, 10 A, 13 A, 16 A | E 14 |
| D02 | 20 A, 25 A, 32 A, 35 A, 40 A, 50 A, 63 A | E 18 |
| D03 | 80 A, 100 A | M 30 × 2 |
The design D03 is used very rarely, because with these high calculation stream NH-fuses proved as more reliable.
D-fuses can switch off independently of their rated current flow of several thousand ampere. In the better and better removed nets with lower internal resistance their identification and cut-off currents are not sufficient often, then in the following the descriptive NH-fuses must be used.
D-fuses have usually with overload and also in the case of short-circuit higher down times than Line protection switch with magnetic short-circuit cause. The latter should not only be preferred from there with house installations due to the repeated usefulness to the fuses. Both for Diazed, as well as for Neozed-fuses there is a base for screwing assembly, for DIN rail assembly and for bus bar assembly (rider bases). For Neozeds-fuse there is additionally fuse load disconnecting switch. Those are fuse bases with integrated load disconnecting switch. Before each change of a protection the base must have the electrical power switched off by a flap present before the fuses. This voltage and the working reliability and security for the user increases load-free changes, since this can come in no case with live construction units into contact. With new versions of these load disconnecting switches the Fuse-cartridge are no longer screwed, but are contacted by spring action.
[edit] NH-fuses
Niederspannungs (low-voltage) Hochleistungs (high speed) fuses, shortly NH-fuses, and is well known under the names measurer protection, sword protection and tank protection (Messersicherung, Schwertsicherung and Panzersicherung). The distinctive characteristics in contrast to the screw type fuses is the clearly larger construction volume as well as the massive contacts at the ends. They can therefore conduct a larger current flow and break it. Usually it's referred to as a high-power fuse that permit a safe switching off of currents within the range of 1.25 kA. NH-fuses are far common in industrial plants, than in public mains electricity applications, e.g. in electrical substations and electrical distribution board, or in house junction box in buildings as a security measurement. It's required to use the TAB 2007 (Technical connection terms) when calculating customer installations TAB 2007 (.pdf 590 KB in German) (technical conditions for connecting electric network users) one separating equipment per counter. Quote:
Separating equipment is a mechanism for separating of the client installation from the distribution network, which also by a customer electro-technical layman can be operated (e.g. Selective main line switch).
This demand is fulfilled by circuit breakers or Neozed load disconnection switch, however not by NH-fuses. They are not used anymore as a protection counter measurement in new installations. NH-fuses also have an activation indicator, which indicates a defective fuse. Depending upon the application a front side indicator is implemented or a center knowing alarm unit, from which the assigned protection is visible from the front. Nearly all manufacturers also offers NH-fuses with 2 activation indicators on (combined activation indicators). There are NH-fuses for different operating classes], e.g. gG, to, gs, gR, acre, gTr, gB. NH-fuses are manufactured in different sizes for different current rating ranges. Size 0 is no longer permitted in new installations.
| Size | Calculation stream | Sword length (approx.) |
|---|---|---|
| 00/000 | 6 - 160 A | 78 mm |
| 0 | 6 - 160 A | 125 mm |
| 1 | 80 - 250 A | 135 mm |
| 2 | 125 - 400 A | 150 mm |
| 3 | 315 - 630 A | 150 mm |
| 4 | 500 - 1000 A | 200 mm |
| 4a | 500 - 1250 A | 200 mm |
[edit] Replacement
NH-Fuse-cartridges are equipped with latches for handling, which can be implemented live or without voltage (isolated). In order to use or pull out of this the fuse-cartridge single-pole in a fuse base, a fuse plug-on grasp is necessary. Powered NH-Fuse-cartridge may only be replaced with suitable protection equipment by an electrical specialist. The protection equipment covers at least a Austeckgriff?? with leather tulip and a helmet with face protection. If necessary an isolation protection mat and isolating gloves may be necessary. Inappropriate pulling of a NH-Fuse-cartridge under load can cause an electric arc, which may cause serious and fatal injuries without protection equipment. So called NH-disconnecting switches facilitate the safety of cartridge replacement. They have a lift-up lid, which takes up the grasp latches and which safety stop grasp replaces. NH-disconnecting switch gives it e.g. in these designs:
- A three-pole switching execution, with all three fuse elements of the three-phase alternating current branch horizontal lines up in a folding employment to be accommodated
- A single-pole switching execution, which consists individual flap in corroding arranged one above the other of three for the three phases. It is very much common in modern transformer stations.
[edit] Rear spar fuses
High voltage high power fuses, shortly HH-fuses, independent protective switching devices are used in medium voltage to 36 kV. In some countries fuses for up to 100 kV is used. They are used in power supply networks and for distribution uses, in order to limit the effects of transfer (short-circuits). Most frequent application is in transformer electric circuits, further uses is in current circles and condenser banks. If it comes to a short-circuit, (or) inside the protection the present fuse wire melts and thereby interrupts the flow. Usually these type of fuses are equipped with an impact pin. This contains a small propellant, which is ignited by an additional thin wire in the protection. He?? withdraws then suddenly from the face one of the contact contacts of the protection. The impact pin affects e.g. the release mechanics of an off-load switch, which switches then the incorrect electric circuit off three pole. High-power fuse means that these fuses can switch off several kA. Some manufacturers have examined fuses for up to 63 kA cut-off current.
A typical Type spectrum is:
- 3 to 7.2 kV with rated currents to 500 A
- 6 to 12 kV with rated currents to 355 A
- 10 to 24 kV with rated currents to 200 A
- 20 to 36 kV with rated currents to 100 A
For the protection of medium voltage transformers and lines are used with larger rated currents network protection of devices.
The dimensions are specified in DIN 43625, therefore world-wide also of the „DIN Fuse“ one speaks. International Electrotechnical Commission (IEC) 60282-1 and/or the German translation Verband der Elektrotechnik (VDE) 0670 part of 4 is the relevant standards, in which the electrical parameters and the type test are described. The interaction of off-load switches and fuses is regular in the IEC 62271-105 (VDE 0671-Teil corresponds to 105). For the allocation of protection and transformer in Germany the VDE 0670 part of 402 is valid.
In other countries, like North American area, fuses are also used in the high voltage range to over 100 kV. Exhibit which however only in electric circuits system-dependently comparatively small short-circuit stream. The advantage is compared with high voltage switches the smaller price. Short-circuits are separated in the high voltage range for power supply due to the momentary achievements high with short-circuit stream by actively steered circuit breaker. With use of fuses it would come during release by the evaporation like an explosion of the lock-wire and the arc to damages in the environment of the protection.
[edit] Miniature and Micro fuses for electronic circuit protection (G-fuses)
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Miniature and micro sized fuses are available with either glass or ceramic hollow tube envelopes with metal end caps at each end.
A fusible link is contained inside the hollow tube and attached between the metal end caps. The tube is filled with either air, or in case of ceramic envelope fuses - with quartz sand. Miniature fuses are available in different lengths and diameters. In Europe the dimensions are 5 mm diameter × 20 mm length, and in USA ¼" × 1 ¼" inch, which corresponds to approximately Ø 6.3 × 32 mm which can also be labeled 6 x 30 mm.
Miniature fuses are most commonly used to protect electronic equipment and sometimes that equipments connection to the electrical power system.
[edit] Marking
On the metal caps is stamped the rated current, the maximum voltage and speed of action, fast or slow. A colour code is sometimes used on micro-fuses.
| Type | Speed of action (German) | Speed of action (English) |
|---|---|---|
| FF | super+speedily | very fast acting |
| F | speedily | fast acting |
| M | central slowly-acting | short time delay |
| T | slowly-acting | medium time delay |
| TT | super+slowly-acting | long time delay |
Characteristics for electronic equipment protection fuses are rated current, rated voltage, speed of action and breaking capacity. The speed of action, fast acting, medium acting or slow blow, differentiates how quickly the fusible length opens. With 10 times the rated current flowing through the fuse the action time may be:
- Fast Acting fuses open in less than 20 ms
- Middle Acting fuses open in less than 50 - 90 ms
- Slow-blow action fuses open in less than 100 - 300 ms
G-fuses are available in ratings of 32 mA - 20 A current.
The voltage and current ratings as well as the action time of USA fuses (Ø 6.3 × 32 mm) differs from European 5 x 20 mm types, and are therefore not interchangeable even if the rating is the same.
[edit] English fuses in compliance with BS 1362
In Great Britain house installations cylindrical fuses with a diameter of ¼" and a length of 1" inch (Ø 6.3 × 25.4 mm) in compliance with BS 1362 are common. The specification calls for sand-filled fuses with ceramic body and metallic contacts at the ends with a 5.5 mm length.
In the BS 1362 standard the release characteristic is only specified for fuses with 3 A (red marking) or 13 A (with-brown marking). Example:
- 3 A fuses
- 0.02 - 80 s with 9 A
- < 0=""> mini putting protection (mini fuse) Standard putting protection (standard fuse) maxi fuse]]
In 1976 a design was developed for flat-stick-fuses standardization but only for safe low-voltages, mainly for use in motor vehicles EN, is used according to DIN 72581/3C. Contrary to the ATS fuses this design has a certification from Underwriters Laboratories (UL). A common label name is ATO - Fuse, (A utomotive Technology Organization); this is a registered registered trademark of the Littelfuse Incorporation , the Plaines, in Illinois, USA. Their sizes and designation:
- Flat mini putting protection (low profiles mini fuse)
- Mini-Put-fuse (mini fuse)
- Standard-Stick fuse (fuse)
- Maxi fuse usual remarks are the standard flat protection and the mini flat protection. The calculation amperage of standard and mini flattening hitting a corner fuses is marked by the color of its plastic body.
| 1 A | 2 A | 3 A | 4 A | 5 A | 7.5 A | 10 A | 15 A | 20 A | 25 A | 30 A | (35 A) | 40 A |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Black | Grey | Violet | Pink | Light brown | Brown | Red | Blue | Yellow | Clearly | Green | Cyan | Orange |
[edit] Strip fuses
Besides there is also strip fuses in the form of a metal strip from a lock plate for high currents over 40 ampere. Frequently these are in direct proximity to starter battery fuse boxes. They are used also in electric vehicles, e.g. in forklift trucks. Strip fuses requires the use of tools for replacement and is therefore considered legal among a layman non-serviceable components.
[edit] Automotive fuses
Automotive fuses protect the wiring and electrical equipment for vehicles. They are generally rated for circuits no higher than 24 volts direct current, but there exists brands of mini[3] and maxi[4] fuses that are modified to be able to work in the 42 volt environment.
[edit] Blade type
Plug-in fuses (also called blade or spade fuses), with a plastic body and two prongs that fit into sockets, are mostly used in automobiles. These types of fuses come in four different physical dimensions: mini (or minifuse or ATM), low-profile mini, ATO (or ATC) and maxi (or maxifuse).
| Type | Dimensions L x W x H | Ampere ratings |
|---|---|---|
| Mini | 10.9 x 3.6 x 16.3 mm | 2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A |
| Low-Profile Mini | 10.9 x 3.81 x 8.73 mm | 2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A |
| ATO | 19.1 x 5.1 x 18.5 mm | 1A, 2A, 3A, 4A, 5A, 7.5A, 10A, 15A, 20A, 25A, 30A, 35A, 40A |
| Maxi | 29.2 x 8.5 x 34.3 mm | 20A, 30A, 40A, 50A, 60A, 70A, 80A, 100A |
It is possible to replace[5] an ATO-type plug-in fuse with a circuit breaker that has been designed to fit in the socket of an ATO-sized fuse holder. These circuit protectors are more expensive than a regular fuse.
[edit] Color-coding
Blade fuses use a color-coding standard. [6] The Mini (ATM) and ATO style fuses use the same color-coding system, while the larger maxi fuses use a different system, with only some colors representing the same current ratings.
Mini, Low-Profile Mini, and ATO Color-coding:
| Color | Current (A) |
|---|---|
| black* | 1 |
| grey | 2 |
| violet | 3 |
| pink | 4 |
| orange/tan | 5 |
| brown | 7.5 |
| red | 10 |
| aqua/blue | 15 |
| yellow | 20 |
| clear/natural | 25 |
| green | 30 |
| blue green* | 35 |
| amber* | 40 |
* = available in ATO fuses only
Maxi Color-coding:
| Color | Current (A) |
|---|---|
| yellow | 20 |
| grey | 25 |
| green | 30 |
| brown | 35 |
| orange | 40 |
| red | 50 |
| blue/aqua | 60 |
| tan | 70 |
| clear/natural | 80 |
| purple | 100 |
[edit] Bosch type
Bosch type fuses (also known as torpedo type fuses) are used in old (often European) automobiles. The physical dimension of this type of fuse is 6x25 mm with conical ends. Bosch type fuses usually use the same color coding for the rated current. The DIN standard is 72581/1. The size of the fuse is: 6x25 mm.
| Color | Ampere |
|---|---|
| yellow | 5A |
| white | 8A |
| red | 16A |
| blue | 25A |
| grey | 40A |
[edit] Lucas type
Lucas type fuses are used in old British made or assembled automobiles. The physical length of this type of fuse is either 1" or 1.25" with conical 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 amp rating that the system should be using; this can be a source of confusion when replacing Lucas fuses with non Lucas fuses.
| Color | Continuous amps | Instantaneous fusing amps | Continuous fusing amps |
|---|---|---|---|
| Blue | 1.5A | 3.5A | 3A |
| Yellow | 2.25A | 5A | 4.5A |
| Red on Yellow | 2.5A | 6A | 5A |
| Green | 3A | 7A | 6A |
| Nut Brown | 4A | 10A | 8A |
| Red on Green | 5A | 12A | 10A |
| Green on Black | 5A | 12A | 10A |
| Red on Brown | 6A | 14A | 12A |
| Light Brown | 7.5A | 18A | 15A |
| Pink | 12.5A | 30A | 25A |
| White | 17.5A | 40A | 35A |
| Purple on Yellow | 25A | 60A | 50A |
| Yellow on Red | 30A | 75A | 60A |
[edit] High voltage fuses
Fuses are used on power systems up to 115,000 volts AC. High-voltage fuses are used to protect instrument transformers used for electricity metering, or for small power transformers where the expense of a circuit breaker is not warranted. For example, in distribution systems, a power fuse may be used to protect a transformer serving 1-3 houses. A circuit breaker at 115 kV may cost up to five times as much as a set of power fuses, so the resulting saving can be tens of thousands of dollars. Pole-mounted distribution transformers are nearly always protected by a fusible cutout, which can have the fuse element replaced using live-line maintenance tools.
Large power fuses use fusible elements made of silver, copper or tin to provide stable and predictable performance. High voltage expulsion fuses surround the fusible link with gas-evolving substances, such as boric acid. When the fuse blows, heat from the arc causes the boric acid to evolve large volumes of gases. The associated high pressure (often greater than 100 atmospheres) and cooling gases rapidly extinguish (quench) the resulting arc. The hot gases are then explosively expelled out of the end(s) of the fuse. Other special High Rupturing Capacity (HRC) fuses surround one or more parallel connected fusible links with an energy absorbing material, typically silicon dioxide sand. When the fusible link blows, the sand absorbs energy from the arc, rapidly quenching it, creating an artificial fulgurite in the process.
[edit] Fuses compared with circuit breakers
Fuses have the advantages of often being less costly and simpler than a circuit breaker for similar ratings. The blown fuse must be replaced with a new device which is less convenient than simply resetting a breaker and therefore likely to discourage people from ignoring faults. On the other hand, replacing a fuse without isolating the circuit first (most building wiring designs do not provide individual isolation switches for each fuse) can be dangerous in itself, particularly if the fault is a short circuit.
High rupturing capacity fuses can be rated to safely interrupt up to 300,000 amperes at 600 V AC. Special current-limiting fuses are applied ahead of some molded-case breakers to protect the breakers in low-voltage power circuits with high short-circuit levels.
"Current-limiting" fuses operate so quickly that they limit the total "let-through" energy that passes into the circuit, helping to protect downstream equipment from damage. These fuses clear the fault in less than one cycle of the AC power frequency. Circuit breakers cannot offer similar rapid protection.
Some types of circuit breakers must be maintained on a regular basis to ensure their mechanical operation during an interruption. This is not the case with fuses, in which no mechanical operation is required for the fuse to operate under fault conditions.
In a multi-phase power circuit, if only one fuse opens, the remaining phases will have higher than normal currents, and unbalanced voltages, with possible damage to motors. Fuses only sense overcurrent, or to a degree, over-temperature, and cannot usually be used independently with protective relaying to provide more advanced protective functions, for example, ground fault detection.
Some manufacturers of medium-voltage distribution fuses combine the overcurrent protection characteristics of the fusible element with the flexibility of relay protection by adding a pyrotechnic device to the fuse operated by external protection relays.
[edit] Fuse Boxes
 MEM rewirable fuse box |
 MEM rewirable fuse holders (30A & 15A) |
 Wylex fuse box |
 fuse wire as sold to UK consumers |
In the UK, older electrical consumer units (also called fuse boxes) are fitted either with semi-enclosed (rewirable) fuses (BS 3036) or cartridge fuses (BS 1361). (Fuse wire is commonly supplied to consumers as short lengths of 5A-, 15A- and 30A-rated wire wound on a piece of cardboard.) Modern consumer units usually contain miniature circuit breakers (MCBs) instead of fuses, though cartridge fuses are sometimes still used, as MCBs are rather prone to nuisance tripping.
Renewable fuses (rewirable or cartridge) allow user replacement, but this can be hazardous as it is easy to put a higher-rated or double fuse element (link or wire) into the holder (“overfusing”), or simply fitting it with copper wire or even a totally different type of conducting object (hairpins, paper clips, nails etc.) to the existing carrier. Such tampering will not be visible without full inspection of the fuse. Fuse wire was never used in North America for this reason, although renewable fuses continue to be made for distribution boards.
The fuse boxes pictured in this section are (right) a MEM consumer unit with four rewirable fuse holders (two 30A & two 15A) installed c.1957 (cover removed); a “Wylex standard” unit with eight rewirable fuse holders.
The “Wylex standard” consumer unit was very popular in the United Kingdom until the wiring regulations started demanding Residual-Current Devices (RCDs) for sockets that could feasibly supply equipment outside the equipotential zone. The design does not allow for fitting of RCDs or RCBOs. Some Wylex standard models were made with an RCD instead of the main switch, but (for consumer units supplying the entire installation) this is no longer compliant with the wiring regulations as alarm systems should not be RCD-protected. There are two styles of fuse base that can be screwed into these units — one designed for rewirable fusewire carriers and one designed for cartridge fuse carriers. Over the years MCBs have been made for both styles of base. In both cases, higher rated carriers had wider pins, so a carrier couldn't be changed for a higher rated one without also changing the base. Cartridge fuse carriers are also now available for DIN-rail enclosures.[7]
In North America, fuses were used in buildings wired before 1960. These "Edison Base" type fuses, would screw into a fuse socket similar to Edison-base incandescent lamps. Ratings were 5, 10, 15, 20, 25, and 30 amperes. To prevent installation of fuses with an excessive current rating, later fuse boxes included rejection features in the fuseholder socket. Some installations use resettable miniature thermal circuit breakers which screw into that fuse socket.
One form of fuse box abuse was to put a penny in the socket, which defeated overcurrent protection and resulted in a dangerous condition.
In the 1950s, fuses in new residential or industrial construction for branch circuit protection were superseded by low voltage circuit breakers.
[edit] British plug fuse
The BS 1363 13 A plug has a BS 1362 cartridge fuse inside. This allows the use of 30 A/32 A (30 A was the original size; 32 A is the closest European harmonised size) socket circuits safely. In order to keep cable sizes manageable these are usually wired in ring mains. It also provides better protection for small appliances with thin flex as a variety of fuse ratings (1 A, 2 A, 3 A, 5 A, 7 A, 10 A 13 A with 3, 5 and 13 being the most common) are available and a suitable fuse should be fitted to allow the normal operating current while protecting the appliance and its cord as well as possible. With some loads it is normal to use a slightly higher rated fuse than the normal operating current. For example on 500 W halogen floodlights it is normal to use a 5 A fuse even though a 3 A would carry the normal operating current. This is because halogen lights draw a significant surge of current at switch on as their cold resistance is far lower than their resistance at operating temperature.
In most other wiring practices the wires in a flexible cord are considered to be protected by the branch circuit overcurrent device, usually rated at around 15 amperes, so a plug-mounted fuse is not used. Small electronic apparatus often includes a fuseholder on or in the equipment, to protect internal components only.
The rating on a BS1362 fuse specifies the maximum current the fuse can pass 'indefinitely' under standard conditions. The fuse will pass higher currents than the rated value for significant periods, depending on how high the overload is. Fuse manufacturers publish tables or graphs of fuse characteristics to allow electrical system designers to specify the correct fuse for the conditions under which it will be expected to operate. One example is the table published by Cooper-Bussmann for their BS1362 fuses[8]. In this table it can be seen that the fuse is specified to be able to carry its rated current for a minimum of 1,000 hours; 1.6 times its rated current for a minimum of 30 minutes; and 1.9 times its rated current for a maximum of 30 minutes. Thus, this BS1362 13A fuse is only rated to break its circuit after carrying 24.7 Amps for 30 minutes.
[edit] Coordination of fuses in series
Where several fuses are connected in series at the various levels of a power distribution system, it is desirable to blow (clear) only the fuse (or other overcurrent device) electrically closest to the fault. This process is called "coordination" and may require the time-current characteristics of two fuses to be plotted on a common current basis. Fuses are selected so that the minor, branch, fuse disconnects its circuit well before the supplying, major, fuse starts to melt. In this way, only the faulty circuit is interrupted with minimal disturbance to other circuits fed by a common supplying fuse.
Where the fuses in a system are of similar types, simple rule-of-thumb ratios between ratings of the fuse closest to the load and the next fuse towards the source can be used.
[edit] Other fuse types
[edit] Resettable fuses
- main article:Resettable fuse
So-called "self-resetting" fuses use a thermoplastic conductive element known as a Polymeric Positive Temperature Coefficient (or PPTC) thermistor that impedes the circuit during an overcurrent condition (by increasing device resistance). The PPTC thermistor is self-resetting in that when current is removed, the device will cool and revert back to low resistance. These devices are often used in aerospace/nuclear applications where replacement is difficult, or on a computer motherboard so that a shorted mouse or keyboard does not cause motherboard damage.
[edit] Thermal fuses
A "thermal fuse" is often found in consumer equipment such as coffee makers or hair dryers or transformers powering small consumer electronics devices. They contain a fusible, temperature-sensitive alloy which holds a spring contact mechanism normally closed. When the surrounding temperature gets too high, the alloy melts and allows the spring contact mechanism to break the circuit. The device can be used to prevent a fire in a hair dryer for example, by cutting off the power supply to the heater elements when the air flow is interrupted (e.g. the blower motor stops or the air intake becomes accidentally blocked). Thermal fuses are a 'one shot', non-resettable device which must be replaced once they have been activated (blown).
[edit] See also
[edit] Notes
- ^ http://edison.rutgers.edu/patents/00438305.PDF - US Patent Office number 438305 "Fuse Block"
- ^ http://www.thefusewarehouse.com/pages/product_markings.htm
- ^ https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/623e2b00-75a4-11dc-b309-005056c00008.pdf Elfa.se: datasheet of mini type fuse
- ^ https://www1.elfa.se/data1/wwwroot/webroot/Z_DATA/7fac31f0-75a4-11dc-b309-005056c00008.pdf Elfa.se: datasheet of maxi type fuse
- ^ ELFA - Electronics supplier of Northern Europe
- ^ Electrical System: Fuses & Circuit Breakers
- ^ "Fuse Carrier Hager" (html). Hager Group website > Products. Hager Group. http://www.hager.com.sg/menu/product/protection-connection/fuse-carrier/800-2343.htm. Retrieved on 2009-02-03.
- ^ "British Plug Top Fuse TDC180". http://www.bussmann.com/library/bifs/2042.PDF. Retrieved on 2007-11-28.
[edit] References
- IEC 60269-1 - Low-voltage fuses - Part 1: General requirements
- IEC 60269-2 - Low-voltage fuses - Part 2: Supplementary requirements for fuses for use by authorized persons (fuses mainly for industrial application) - Examples of standardized systems of fuses A to I
- IEC 60269-3 - Low-voltage fuses - Part 3: Supplementary requirements for fuses for use by unskilled persons (fuses mainly for household and similar applications) - Examples of standardized systems of fuses A to F
- IEC 60269-4 - Low-voltage fuses - Part 4: Supplementary requirements for fuse-links for the protection of semiconductor devices
[edit] External links
 |
Wikimedia Commons has media related to: Fuses |
- [1] Len Lundy, "The fuse-selection checklist: a quick update" EDN Magazine 26 Sept 1996 p121
- [2] Information on circuit protection, surface mount fuses, axial lead & cartridge fuses, blade terminal & special mount fuses, fuseholders, fuse blocks & clips and military fuses and fuseholders
- [3] for the Bussmann manual of fuse selection
- Fuses vs MCBs
- [4] Technical information on circuit protection, fuses, fuse holders, clips, blocks & accessories
