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Glossary

Agency Approvals - PTCs are recognized under the Component Program of Underwriters Laboratories to UL Thermistor Standard 1434. The devices have also been certified under the CSA Component Acceptance Program. Approvals for fuses include recognition under the Component Program of Underwriters Laboratories and the CSA Component Acceptance Program.

Ambient Temperature - Refers to 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.

Amorphous - Without crystallization in the ultimate texture of a solid substance. Used to describe the material structure in the tripped state of a Multifuse® device.

Ampere - The SI unit of measure for electrical current. The unit of electrical current or rate of flow of electrons. 1 ampere = 1 coulomb of charge/second.

Carbon Black - A conductive material used in Multifuse® devices to provide a path for current flow under normal operating conditions.

Conductive Plastic - A plastic material, such as a polymer, containing conductive particles, such as carbon black, that provide a path for current flow.

Current - The flow of electric charge that transports energy from one place to another. Measured in amperes, where one ampere is the flow of 6.25 x10^18 electrons (or protons) per second.

Current, Hold (Ihold ) - The maximum current a Multifuse® device can pass without interruption.

Current, Maximum (IMAX ) - The maximum fault current a Multifuse® device can withstand without damage at the rated voltage.

Current Rating - The nominal amperage value marked on the fuse. It is established by the manufacturer as a value of current which the fuse can be loaded to, based on a controlled set of test conditions (see Rerating).

Current, Trip (I trip ) - The minimum current that will switch a device from the low resistance to the high resistance state.

Date Code - A number used to let the manufacturer know the date the part was fabricated as well as the plant location.

Derating - Fuses are essentially temperature-sensitive devices. Even small variations from the controlled test conditions can greatly affect the predicted life of a fuse when it is loaded to its nominal value, usually expressed as 100% of rating. The fuse temperature generated by the current passing through the fuse increases or decreases with ambient temperature change.

Electrode - A device or material that emits or controls the flow of electricity. Nickel and Copper elements are used in Multifuse® devices to aid even distribution of current across the surface of the device.

Fault Current - The peak current that flows through a device or wire during a short circuit or arc back.

Flux - A material used to promote the joining of metals in soldering. Rosin is widely used in soldering electronic parts.

Form Factor - The package that holds the chemical make-up of polymer and carbon. PPTCs are packaged in the following forms; radial, axial, surface mount chips, disks, and washers.

Fuse - A current limiting device used for protection of equipment as well as personnel. Typically a wire or chemical compound which breaks a circuit when the current exceeds a rated value.

Fuse Resistance - The resistance of a fuse is usually an insignificant part of the total circuit resistance. Since the resistance of fractional amperage fuses can be several ohms, this fact should be considered when using them in low-voltage circuits. Most fuses are manufactured from materials which have positive temperature coefficients, and therefore, it is common to refer to cold resistance and hot resistance (voltage drop at rated current), with actual operation being somewhere in between. The factory should be consulted if this parameter is critical to the design analysis. Resistance data on all of our fuses is available on request.

Hysteresis - The period between the actual beginning of the signaling of the device to trip and the actual tripping of the device.

Interrupting Rating - Also known as breaking capacity or short circuit rating, the interrupting 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.

Leakage Current - An undesirable small value of stray current that flows through a device after the device has changed state to a high resistance mode.

Let through Current - The amount of current though a circuit after a device is signaled to trip and the device is at full operation limiting current.

Maximum Fault Current - The Interrupting Rating of a fuse must meet or exceed the Maximum Fault Current of the circuit.

Ohm - The SI unit of measure for electrical resistance. 1 ohm = 1 Volt/1 ampere.

Ohm's Law - The current in a circuit varies in direct proportion to the potential difference or emf and in inverse proportion to resistance. Current = Voltage/Resistance. A potential difference of 1 volt across a resistance of 1 ohm produces a current of 1 ampere.

Overload Current Condition - The current level for which protection is required. Fault conditions may be specified, either in terms of current or, in terms of both current and maximum time the fault can be tolerated before damage occurs. Time-current curves should be consulted to try to match the fuse characteristic to the circuit needs, while keeping in mind that the curves are based on average data.

Polymer - A synthetic plastic material consisting of large molecules made up of a linked series of repeated simple monomers. The insulating medium used in Multifuse® devices which maintains the carbon chains in suspension during overcurrent while permitting the carbon chains to form during normal operation.

Polymeric Positive Temperature Coefficient (PPTC) - A characteristic of Multifuse® devices that describes a large increase in resistance as the device reaches its trip temperature.

Power - The ratio of energy per time. Power is measure in Watts, and Joules. Power = Current x Voltage. Where 1 amp x 1 volt = 1 watt.

Power Dissipation (Pd ) - Power dissipated from the device while in the tripped state.

Power Surge - A sudden series of pulses or spikes in the voltage or current of a circuit. The circuit is usually protected against power surges.

Pulses - The general term "pulses" is used in this context to describe the broad category of wave shapes referred to as "surge currents," "start-up currents," "inrush currents," and "transients," Electrical pulse conditions can vary considerably from one application to another. Different fuse constructions may not all react the same to a given pulse condition. Electrical pulses produce thermal cycling and possible mechanical fatigue that could affect the life of the fuse. The start-up pulse should be defined and then compared to the time-current curve and l2t rating for the fuse. Nominal melting l2t is a measure of the energy required to melt the fusing element and is pressed as "Ampere Squared Seconds" (A2 Sec.).

Resistance - A property of conductors which - - depending on their material, dimensions, and temperature - - determines the current produced by a given difference of potential.

Resistance, Initial (R Min - R Max ) - The resistance range of the Multifuse® devices, as received from the factory.

Resistance, Post Trip (R 1max ) - The maximum post-trip resistance one hour after a Multifuse® device has been tripped and power has been removed.

Resistance, Post Reflow (R 1max ) - The maximum resistance one hour after a Multifuse® surface mount device has been reflow soldered.

Trip Cycle Life - A test used to determine the number of trip cycles (at V Max & I Max ) a Multifuse® device will sustain without failure.

Trip Endurance - A test used to determine the duration of time a Multifuse® device will sustain its maximum rated voltage in the tripped state without failure.

Vibration - A test used to evaluate the physical effects, if any, and constructional integrity of a Multifuse® device when subjected to vibration. The room temperature resistance is measured before and after conditioning.

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