Fuse Mounting Accessories Page 10 Fuse & Mounting Accessories

2017 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 03/03/17 FUSE Circuit Protection Products and Mounting Accessories Fuse Selection Checklist The application guidelines and product data in this guide are intended to provide technical information that will help with application design. Since these are only a few of the contributing parameters, application testing is strongly recommended and should be used to verify performance in the circuit/application. Many of the factors involved with fuse selection are listed below. For additional assistance with choosing fuses appropriate to you requirements, contact your Littelfuse products reprentative.: Selection Factors 1. Normal operating current 2. Application voltage (AC or DC) 3. Ambient temperature 4. Overload current and length of time in which the fuse must open 5. Maximum available fault current 6. Pulses, Surge Currents, Inrush Currents, Start-up Currents, and Circuit Transients 7. Physical size limitations, such as length, diameter, or height 8. Agency Approvals required, such as UL, CSA, VDE, METI, MITI or Military 9. Fuse features (mounting type/form factor, ease of removal, axial leads, visual indication, etc.) 10. Fuseholder features, if applicable and associated re-rating (clips, mounting block, panel mount, PC board mount, R.F.I. shielded, etc.) 11. Application testing and verification prior to production Littelfuse is at your service to help solve your electrical protection problems. When contacting Littelfuse sales engineers, please have all the requirements of your applications available. Requests for quotes or assistance in designing or selecting special types of circuit protection components for your particular applications are also welcome. In the absence of special requirements, Littelfuse reserves the right to make appropriate changes in design, process, and manufacturing location without prior notice. 1. NORMAL OPERATING CURRENT: The current rating of a fuse is typically derated 25% for operation at 25C to avoid nuisance blowing. For example, a fuse with a current rating of 10A is not usually recommended for operation at more than 7.5A in a 25C ambient. For additional details, see RE-RATING in the previous section and AMBIENT TEMPERATURE below. 2. APPLICATION VOLTAGE: The voltage rating of the fuse must be equal to, or greater than, the available circuit voltage. For exceptions, see VOLTAGE RATING. 3. AMBIENT TEMPERATURE: The current carrying capacity tests of fuses are performed at 25C and will be affected by changes in ambient temperature. The higher the ambient temperature, the hotter the fuse will operate, and the shorter its life. Conversely, operating at a lower temperature will prolong fuse life. A fuse also runs hotter as the normal operating current approaches or exceeds the rating of the selected fuse. Practical experience indicates fuses at room temperature should last indefinitely, if operated at no more than 75% of catalog fuse rating. Ambient temperature effects are in addition to the normal re-rating, see example. Example: Given a normal operating current of 2.25 amperes in an application using a 229 series fuse at room temperature, then: Normal Operating Current Catalog Fuse Rating = - - - - - - - - - - 0.75 - or - 2.25 Amperes ------- = 3 Amp Fuse (at 25C) 0.75 This charts shows typical ambient temperature effects on current carrying capacity of Littelfuse products. For specific re-rating information, please consult the product data sheet www.littelfuse.com or contact a Littelfuse representative. Curve A: Thin-Film Fuses and 313 Series (.010 to .150A) Curve B: FLAT-PAK , TeleLink , Nano 2 , PICO , Blade Terminal and other leaded and catridge fuses Curve C: Resettable PTC's

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