Fuse Mounting Accessories Page 12 Fuse & Mounting Accessories

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 03/03/17 FUSE Circuit Protection Products and Mounting Accessories .001 .002 .003 .004 .005 .006 Time (Seconds) Current (Amperes) 2 4 6 8 10 Normal Operating Current l t Pulse Energy 2 CHART 1 WAVESHAPES FORMULAS t t t 1 i p i p i p i p i p i b i p F E D C B A OR t i = k I 2 t = i p 2 t i = i p -kt I 2 t = (1/3)(i p 2 + i p i b + i b 2 ) t i = i p sin t I 2 t = (1/2) i p 2 t I 2 t = (1/3) i p 2 t i = kt 2 OR i = i p (1-kt) 2 I 2 t = (1/5) i p 2 t i = i p e -kt ) I 2 t (1/2) i p 2 t 1 CHART 2 PULSE CYCLE WITHSTAND CAPABILITY 100,000 Pulses Pulse I 2 t = 22% of Nominal Melting I 2 t 10,000 Pulses Pulse I 2 t = 29% of Nominal Melting I 2 t 1,000 Pulses Pulse I 2 t = 38% of Nominal Melting I 2 t 100 Pulses Pulse I 2 t = 48% of Nominal Melting I 2 t 100000 10000 1000 100 10% 100% Number of Pulses Pulse I 2 t / Average Melting I 2 t Note: Adequate time (10 seconds) must exist between pulse events to allow heat from the previous event to dissipate. conditions specified by Underwriters Laboratories. The primary objective of these UL test conditions is to specify common test standards necessary for the continued control of manufactured items intended for protection against fire, etc. A copper dummy fuse is inserted in the fuseholder by Underwriters Laboratories, and then the current is increased until a certain temperature rise occurs. The majority of the heat is produced by the contact resistance of the fuseholder clips. This value of current is considered to be the rated current of the fuseholder, expressed as 100% of rating. Some of the more common, everyday applications may differ from these UL test conditions as follows: fully enclosed fuseholders, high contact resistance,air movement, transient spikes, and changes in connecting cable size (diameter and length). Even small variations from the controlled test conditions can greatly affect the ratings of the fuse-holder. For this reason, it is recommended that fuseholders be derated by 40% (operated at no more than 60% of the nominal current rating established using the Underwriter Laboratories test conditions, as previously stated). 11. TESTING: The factors presented here should be considered in selecting a fuse for a given application. The next step is to verify the selection by requesting samples for testing in the actual circuit. Before evaluating the samples, make sure the fuse is properly mounted with good electrical connections, using adequately sized wires or traces. The testing should include life tests under normal conditions and overload tests Under fault conditions, to ensure that the fuse will operate properly in the circuit. FIGURE 1 Fuse Selection Checklist (cont.)

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