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Connecting two fuses in parallel

Discussion in 'General Electronics Discussion' started by Micik, Jan 18, 2015.

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  1. Micik

    Micik

    2
    0
    Jan 18, 2015
    Hello to all,

    I have one fuse dimensions 5mmx20mm blown in a power supply unit. It is written on it: T8A 250V. Since I don't have exact to replace it, I wonder could I connect two fuses with same dimensions but 4A 250V in parallel?
    I was thinking to place one fuse in the holder and another one just to solder on the top. Since both fuses are identical characteristic I think there will not be a problem.

    Is there some potential problems that I can expect?


    Thank you
     
  2. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    You can but you will have to de-rate the current rating and voltage rating of each fuse.
    Adam
     
  3. Micik

    Micik

    2
    0
    Jan 18, 2015
    Hello Adam,

    can you please elaborate what you think under de-rate current and voltage rating. Does it mean that paralel combination of two fuses 4A 250 V will not be the equivalent to 8A 250V. Will this combination have lower current rating?

    Thanks
     
  4. davenn

    davenn Moderator

    13,671
    1,892
    Sep 5, 2009
    This is really not a good idea
    If one fuse blows before the other and it takes xx milliseconds for the second fuse to blow, you run the risk of equipment damage

    Also, because of minor variations in the fuse manufacturing, you may find one of the 2 fuses will take more of the load sharing and be prone to popping more often

    Gosh, just get the correct fuse

    Dave
     
  5. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    You can run fuses this way its not a problem. The voltage is derated by 15% but the current could be as low as 30%. But as Dave said it is always best to use the correct fuse.
    Adam
     
    Last edited: Jan 18, 2015
  6. Arouse1973

    Arouse1973 Adam

    5,164
    1,081
    Dec 18, 2013
    Yes correct at best case you get 8A but worst case it could be 5.4A.
    Adam
     
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