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August 26, 2009
Fuse Selection Guide

It’s been several months now since I started sending out the OptiFuse Daily Blog...I’ve received so many great comments and words of encouragement...seemingly almost on a daily basis...

One of the comments I received yesterday was from John M.an engineer in the Midwest who wrote..."you’ve been sending me a lot of great information but there doesn’t seem to be any systematic approach to your e-mails...can you please send me a step-by-step guide to designing fuses?"

Ok John...I’ll do just that...I’ve put together a step-by-step fuse selection guide that will help you engineer and select the proper fuse or circuit breaker for your application...

There’s about 15 steps and/or considerations...so I can’t do it in one e-mail...but over the next few weeks...I’ll go over each step...I’ll also post the complete fuse selection guide on the OptiFuse website once I’m finished.

In order to select the proper protective device you need to consider the following factors:

  1. What is the normal operating current of the circuit?
  2. What is the operating voltage?
  3. Is the circuit AC or DC?
  4. What is the operating ambient temperature?
  5. What is the available short-circuit current?
  6. What is the maximum allowable I²t?
  7. Are there in-rush currents available?
  8. Is the protective device being used for short-circuit protection, over-load protection, or both?
  9. What are the physical size limitations?
  10. Is the PCB surface mount or thru-hole?
  11. Does the fuse need to be "field-replaceable"?
  12. Is resettability an issue?
  13. What safety agency approvals are needed?
  14. How will I mount the device?
  15. What are the cost considerations?
Many of the above topics have already been discussed in this forum so in those cases I’ll just provide a quick review and a link to the original blog...for other topics I’ll explain the topic is a bit more detail.  Within a week or two... you’ll have a comprehensive over-current protection guide all found in one place...

Thank you once again for your continued support of OptiFuse where we are committed to education of our customers

Jim Kalb


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