Fuse Terminology

Ampere Rating
The current carrying capacity of a fuse. When a fuse is subjected to a current above its ampere rating, it will open the circuit after a predetermined period of time.

Ambient Temperature
The temperature of the air immediately surrounding the fuse and is not to be confused with 'room temperature'. The fuse ambient temperature is appreciably higher in many cases, because it is enclosed (as in a panel mount fuseholder) or mounted near other heat producing components, such as resistors, transformers, etc.

American Wire Gauge (AWG)
The American Wire Gauge (AWG) chart was created to classify cables with a single, solid, round conductor. The AWG of a stranded wire is determined by the total cross-sectional area (mm²) of the conductor. Because there are also small gaps between the strands, a stranded wire will always have a slightly larger overall diameter than a solid wire with the same AWG number. Increasing AWG numbers give decreasing wire diameters ie. AWG #12 is a thinner wire than AWG #10.

Anti-Surge Fuse (See Slow Acting Fuse)

Bus / Bussed / Bussing
The process of joining multiple poles or circuits to a single connection point ie. cable, stud or terminal. This can reduce wiring and termination of each individual pole. A bus can be used to provide a single power or ground connection to multiple circuits. We sell a range of bussed fuse holders that utilise an internal bus to distribute power from a single input to each fuse circuit in the holder.

Breaking Capacity(See interrupting rating)

Cartridge Fuse
A fuse consisting of a current responsive element inside a fuse tube with terminals at both ends.

Circuit Breakers
A thermal circuit breaker is designed to protect a circuit from overload, but can be reset once the fault is rectified. Learn more about these devices in our circuit breaker editorial.

Clearing Time
The total time between the beginning of the overcurrent and the final opening of the circuit at rated voltage by an overcurrent protective device. Clearing time is the total of the melting time and the arcing time.

Current Limitation
A fuse operation relating to short circuits only. When a fuse operates in its current limiting range, it will clear a short circuit in less than 1/2 cycle. Also, it will limit the instantaneous peak let-thru current to a value substantially less than that obtainable in the same circuit if that fuse was replaced with a solid conductor of equal impedance.

Derating
In 25 deg.C ambient temperatures, it is recommended that fuses operate at no more than 75% of the nominal current rating established using the controlled set of test conditions. Contact us for more information.

Dual Element Fuse
Fuse with a special design that utilizes two individual elements in series inside the fuse tube. One element, the spring actuated trigger assembly, operates on overloads up to 5-6 times the fuse current rating. The other element, the short circuit section operates on short circuits up to their interrupting rating.

Fast Acting Fuse
A fuse which opens on overload and short circuits very quickly. This type of fuse is not designed to withstand temporary overload currents associated with some electrical loads.

Fast Blow Fuse (See Fast Acting Fuse)

Fuse Characteristics
The characteristics of a fuse design refers to how rapidly the fuse responds to various current overloads. Fuse characteristics can be classified into three general categories: very fast acting, fast acting, or slo-blo. The distinguishing feature of slo-blo fuses is that these fuses have additional thermal inertia designed to tolerate normal initial or start-up overload pulses.

Ignition Protected
An electrical device that has been certified Ignition Protected is suitable for use in marine engine compartments and fuel tank spaces. There are generally two test standards accepted by the Marine Industry – SAE J1171, External Ignition Protection of Marine Electrical Devices and UL1500, Ignition- Protection Test for Marine Products. The requirements and test procedures for the two standards are similar. Essentially, three test results will allow a device to be certified IGNITION-PROTECTED.
1. The device or component is constructed so that a defined flammable hydrocarbon mixture surrounding the device will not ignite if a normal electrical arc, spark or heat source ignites the mixture inside the device.
2. Under the conditions of item 1, the device or component has insufficient energy to ignite the mixture inside the device.
3. Under the conditions of item 1, the source of ignition is hermetically sealed from the surrounding mixture. An Ignition- Protected device is not necessarily Explosion-Proof. Explosion-Proof devices are as applied to U.S. Coast Guard inspected vessels or as defined by the National Electric Code.

Interrupting Rating (Breaking Capacity)
Also known as the breaking capacity or short circuit rating is the maximum approved current which the fuse can safely interrupt at rated voltage. During a fault or short circuit condition, a fuse may receive an instantaneous overload current many times greater than its normal operating current. Safe operation requires that the fuse remain intact (No explosion or body rupture) and clear the circuit.
LBC = Low Breaking Capacity
HRC =High Breaking Capacity
EBC = Enhanced Breaking Capacity

Fuse
An overcurrent protective device with a fusible link that operates and opens the circuit in an overcurrent condition.

High Speed Fuses
Fuses with no intentional time delay in the overload range and designed to open as quickly as possible in the short circuit range. These fuses are often used to protect solid state devices.

Ohm
The unit of measure for electric resistance. One Ohm is the amount of resistance that will allow one Ampere to flow under a pressure of one Volt.

Ohm's Law
The relationship between voltage, current, and resistance, expressed by the equation E = IR, where E is the voltage in Volts, I is the current in Amperes, and R is the resistance in Ohms.

Overcurrent
A condition which exists in an electrical circuit when the normal load current is exceeded. Overcurrents take on two separate characteristics -overloads and short circuits.

Overload
Can be classified as an overcurrent which exceeds the normal full load current of a circuit. Also characteristic of this type of overcurrent is that it does not leave the normal current carrying path of the circuit - that is, it flows from the source, through the conductors, through the load, back through the conductors, to the source again.

Peak Let-Thru Current, Ip
The instantaneous value of peak current let thru by a current limiting fuse, when it operates in its current limiting range.

Resettable Fuses / PTC´s
You will find detailed information regarding these devices in our this datasheet.

Resistive Load
An electrical load which is characteristic of not having any significant inrush current. When a resistive load is energized, the current rises instantly to its steady state value, without first rising to a higher value.

R.M.S. Current
The R.M.S. (root mean square) value of any periodic current is equal to the value of a direct current which, flowing through a resistance, produces the same heating effect in the resistance as the periodic current does.

Semiconductor Fuses
Fuses used to protect solid state devices. See "High Speed Fuses".

Short Circuit
Can be classified as an overcurrent which exceeds the normal full load current of a circuit by a factor many times (tens, hundreds or thousands) greater. Also characteristic of this type of overcurrent is that it leaves the normal current carrying path of the circuit, taking a "short cut" around the load and back to the source.

Slow Acting Fuse
A fuse with a built-in delay that allows temporary and harmless inrush currents to pass without opening, but is designed to open on sustained overloads and short circuits.

Slow Blow Fuse (See Slow Acting Fuse)

Super Rapid Fuse (See High Speed Fuses)

Thermal Fuse / Thermal Cutoff´s
You will find detailed information regarding these devices in our this datasheet.

Voltage Rating
The maximum open circuit voltage in which a fuse can be used, yet safely interrupt an overcurrent. Exceeding the voltage rating of a fuse impairs its ability to clear an overload or short circuit safely.

Ultra Rapid Fuse (See High Speed Fuses)

Very Fast Acting Fuse (See High Speed Fuses)

Wire Gauge
This is a measurement of how large a wire is, either in diameter (solid wires) or cross sectional copper area (stranded wires). The cross sectional area is represented as mm² and typcially excludes the outer insulation. Wire gauge is useful to determine the amount of electric current a wire can safely carry, as well as its electrical resistance.