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Fast and Slow Blow Fuse

By on April 25, 2012

SMPS usually use slow blow fuse and if you replace it with a fast blow fuse (with the same ampere rating) chances is high the fuse will blow again. It can blow immediately or after using the equipment for sometimes. The reason you do not put back a slow blow fuse is either your compartment have no more stock or you wat to save the money. A slow blow fuse price is very much higher than a fast blow fuse.

If your compartment totally do not have anymore slow blow fuse, you could use a fast blow fuse  for testing but with atleast 1amp higher than the original  one. I have seen people use about 2 amp higher. This mean if the slow blow fuse is 3 or 3.15 amp they replace it with a 5 ampere. Do it only for testing purposes and not for permanent usage.

Remember, when replacing a fuse be it a slow blow fuse or fast blow fuse  always use back the the same type and with original rating. I do not want you to face any legal action just incase if you have repaired an equipment and the whole equipment burn down in your customer place.  Even when you sleep you will have a peaceful night and need not worry if the equipment will burn.



  1. beh

    April 26, 2012 at 1:42 am

    thanks for good article also i added this link:

  2. Galib

    April 26, 2012 at 6:55 pm

    Whooopssss ...... I did not know before about <b>Slow Blow Fuse and Fast Blow Fuse</b> !!! I just buy it from shop with $0.1 and replace it ......... that's all what I do !! <b>Fast Blow Fuse -</b> you mean product of <b>Fake Company .</b>

    • Jestine Yong

      April 27, 2012 at 1:48 am

      Hi Galib,

      The cheap one is usually fast blow fuse. There is a different when you compare the outlook of a fast and slow blow fuse.


  3. Galib

    April 26, 2012 at 7:05 pm

    By the way - What happens with that  NCP1203P60 IC . Did that work with new NCP1203P60 instead of 1203P60 ?

    • Jestine Yong

      April 27, 2012 at 1:49 am

      HI Galib,

      Have not try that yet because at the moment do nothave the NCP1203P60 IC.


  4. beh

    April 30, 2012 at 1:23 pm

    please tell me what are the differnce between <b>  and </b> you are using this two symboles in your comments i do not know the meanings . and when you use b and when you use /b and why and so and so...........................................................................................thanks

  5. Marulitua Hutabarat

    May 10, 2012 at 6:34 am

    Hi Jestine,
    Thanks for the article.
    How to distinguish the slow blow fuses and the fast ones physically?
    Best Regards,
    Marulitua H.

    • Jestine Yong

      May 11, 2012 at 12:51 am

      HI marulitua,

      The end cap of slow blow fuse have logos and marked very clear. The fast blow fuse end cap does not have any logo. older type of slowblow fuse the internal wire is like a spring or have a dot in the center. The fast blow fuse have a very fine wire in the center.



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