FUSE TERMINOLOGY - Cooper Industries

1 1 fuse TERMINOLOGYA mbient Temperature*The temperature of the air surrounding the TimeThe amount of time that passes from the instant the fuse ele-ment or link has melted until the overcurrent is interrupted CurrentRefer to ALTERNATING CURRENT. A-C current is asymmetricalwhen the loops about a zero axis are unequal (offset). This con-dition is usually associated with the first five or less cycles offault current flow in a circuit that has inductive reactance. Allpower distribution systems have a variable amount of *The part of the fuse which encloses the fuse elements and sup-ports the contacts.

2 Also referred to as cartridge, tube or FaultThis refers to a zero impedance fault considered at locations ina power system where the maximum value of available fault cur-rent is specially designed narrow portion of a fuse link that heatsfastest under overcurrent conditions to open fuse *A fuse consisting of a current responsive element inside a fusebody with contacts on both Size*The range of voltage and ampere ratings assigned to a cartridgeof specific dimensions and I2t (Ampere Squared Seconds)*The measure of heat energy developed as a result of currentflow between the time that current begins to flow and until thefuse clears the circuit.

3 I2 stands for the square of the effectivelet-through current and t stands for the time of current flow inseconds. The term I2t also applies during the melting or arcingportions of the clearing time and is referred to as melting or arc-ing I2t respectively. Clearing I2t is the sum of melting I2t and arc-ing TimeThis is the total opening time of a fuse from the occurrence of anovercurrent until the fuse stops current flow. This is the sum oflink melting and arcing *The external metallic parts of the fuse used to complete the cir-cuit. Also referred to as ferrules, caps, blades or LimitationA fuse provides current limitation when the link melts undershort-circuit conditions to interrupt the current flow before thepeak of the first one-half cycle of prospective current and thecurrent flow is stopped within one-half fuse *A fuse that meets the following three conditions: 1) interrupts allavailable overcurrents within its interrupting rating; 2) within itscurrent-limiting range, limits the clearing time at rated voltage toan interval equal to, or less than, the first major or symmetricalcurrent loop duration.

4 And 3) limits peak let-through current to avalue less than the available peak Range*A range of available currents from the threshold current to theinterrupting current rating of a Rating*The A-C or D-C ampere rating which the fuse is capable of car-rying continuously under specified refers to intentional delay designed into the overloadrange operation of a fuse and is meaningless except as definedby a fuse manufacturer. Other words used to indicate delay butnot UL defined may be Time-Lag , Delay Type , Element FuseThe words Dual Element and Time-Delay appear on thelabels of Class R fuses to indicate that the fuse has UL defineddelay in the overload operation range of a minimum of 10 sec-onds at 500% of the fuse amperes rating.

5 A Dual Element fusehas separate overload and short-circuit elements and is consid-ered a true time-delay fuse design as opposed to other typesof construction to obtain Current (Ie) Effective and RMS both refer to the heating effect value of anA-C current equivalent to a steady flow of a D-C current. Effective let-through amperes (Ie) refers to the heating effectvalue of the current allowed to flow during the clearing of a short-circuit AlloyThis is an alloy of lead, tin and other metals that, by metallurgi-cal definition, changes from a solid directly to a liquid when itsmelting point is reached.

6 This alloy is used in EDISON Class Rfuses for dependable overload element FuseThis is a fuse with no intentional time-delay designed into theoverload range. Sometimes referred to as a single elementfuse or non-delay fuse .Fault CurrentShort-circuit current that flows partially or entirely outside theintended normal load current path of a circuit or may be from hundreds to many thousands of cylindrical brass, bronze or copper mounting terminals offuses with amps ratings up to 60 amperes. The cylindrical termi-nals at each end of a fuse fit into fuse *A material used to fill a section or sections of a fuse which aidsin arc *A protective device which opens by the melting of a current sen-sitive element during specified overcurrent SinkA mass of metal, usually copper or a eutectic alloy, used in theoverload element of Class R fuses to provide accurate timedelay by absorbing heat from an overload current flow through Rupturing Capacity (HRC)HRC is used by Canadian and British Standards as an equiva-lent to the interrupting rating of a fuse .

7 HRC must be at least100,000 amperes.*From ANSI/ NEMA FU1-862 fuse TERMINOLOGYI2t (Amperes Squared Seconds)This is a value obtained by multiplying an effective currentsquared by the time of flow of the current in seconds. It is not aheat energy value, but represents heat energy for comparisonpurposes. Some common uses are to determine fuse selectivityand to select current limiting fuses that will limit this value to becompatible with the withstandability of semi-conductors thathave n I2t Rating*A rating based upon the highest rms alternating current or directcurrent which the fuse is required to interrupt under specific BladeA flat copper mounting blade (terminal) at each end of fusesrated 70 through 6000 amperes.

8 Knife blades may be mountedin fuse clips or bolted in place via blade holes, depending on thefuse have internal construction like fuses but provide onlyshort-circuit protection and no overload protection. They areintended for special applications such as Cable Limiters andWelder fusible portion of the fuse which melts, or reacts by othermeans, to clear the circuit during an overcurrent condition. Alsoreferred to as an StressWhen thousands of amps of short-circuit current flows throughequipment and conductors, strong magnetic fields are devel-oped that may cause serious damage unless adequate physicalbracing is applied.

9 Force is proportional to the value of peak cur-rent squared. This force is usually reduced by current limitingfuses as compared to other overcurrent protective Energy*A condition under which, in a specified time, the maximumamount of heat possible is generated in the fuse before Time*The time from the initiation of an overcurrent to the instant arc-ing begins inside a fuse *A fuse which cannot be restored for service after Frequency Recovery Voltage*The normal frequency rms voltage impressed upon the fuseafter the circuit has been interrupted and after high frequencytransients have DiagramAn electrical diagram that shows one line to represent two ormore conductors for FuseA term used to identify a non-renewable Class H fuse asopposed to a Class H fuse with replaceable

10 Iinks. See non-renewable fuse .Overcurrent*Any current in excess of the fuse current value of overcurrent usually considered to be up to about 10times the ampere rating of an overcurrent protection device orcircuit ampere Arc Voltage*The maximum peak voltage across the fuse during the Let-Through Current (Ip)*The maximum instantaneous current through a fuse during inter-ruption in its current-limiting *A designated limit of operating characteristics based on Feature*The physical characteristic of a fuse and fuseholder (slot, groovepin or overall dimension) which prevents substitution by otherclasses of fuse *A fuse which can be readily restored for service after operationby the replacement of the renewal Element (Renewal Link)*That part of a renewable fuse that is replaced after each inter-ruption to restore the fuse to operating Current Refer to Fault fuse Refer to Fast-Acting fuse (UL)A UL fuse class per Standard 198G that defines certain smallfuses not intended for branch circuit StressHeat builds up in equipment and conductors during the time ofovercurrent flow that may cause thermal stress and potentialthermal (heat)