Why didnt fuse blow?

Discussion in 'General Electronics Chat' started by bwd111, Sep 12, 2013.

  1. bwd111

    Thread Starter Member

    Jul 24, 2013
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    I used a 240 volt 3 amp rated fuse on a system that calls for 460 v 3 amp fuse and 3 weeks later the fuse hasnt blown and I want to know why?
     
  2. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Using the wrong voltage fuse is not wise. Did your load exceed the 3 amps that the fuse is rated for?
    Fuses are designed to open when the listed CURRENT is exceeded
    not the voltage.
     
  3. bwd111

    Thread Starter Member

    Jul 24, 2013
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    Amps stayed the same as voltage never decreased to raise amps.
     
  4. praondevou

    AAC Fanatic!

    Jul 9, 2011
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  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    [​IMG]Fuses aren't rated for voltage carrying purposes, the rating come into effect when and if the fuse blows, you do not want a low voltage rated fuse on a high supply, the construction of which may allow conduction after blowing.
    This is one reason that re-wireable fuses are no longer allowed under NEC.
    Max.
     
  6. wmodavis

    Well-Known Member

    Oct 23, 2010
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    How much current is flowing through the fuse? Might be a clue. A big clue!
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    On a fuse, there is something called 'sweep through rate' this is the efficiency that it operates at the rated current.
    Their are also fuses known as Rectifier fuses, probably should be called semiconductor fuses?
    They have extremely low delay and sweep through very fast in order to protect a fast switching semiconductor circuit.
    They usually are not cheap, however.
    Max.
     
  8. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    While fuses aren't actually rated for their voltage carrying, they are voltage rated. The higher the voltage rating on a fuse, the more robust/strong the outer case is.

    A 250V glass fuse is OK in a 12V circuit, but a 12V fuse isn't OK in a 250V circuit.
     
  9. WBahn

    Moderator

    Mar 31, 2012
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    A just slightly different way to look at it is to realize that the fuse, while it is good, neither knows nor cares what the voltage of the line is that it is in. All it knows is the voltage between its terminals, which is kept very close to zero voltage as long as it is good. Voltage can be developed across a fuse only after it blows, hence any voltage rating must be applicable to the after-blown (or while-blowing) situation.
     
  10. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Did you mean "never increased" rather than "never decreased"?

    I would think voltage rating may also have something to do with the ability of the fuse to clear or quench any arcing within the fuse body at the time of an over-current fault, that might lead to ongoing current conduction even after the wire element has melted or vaporized. This can be a particular issue with using fuses to protect DC systems rather than AC systems. At least in an AC system it's likely the fault current will transit zero value at some instant, thereby increasing the likelihood of any arc formed being quenched. With DC faults there is no current zero during the fault clearing period and an arc may persist within the fuse body until the fuse self destructs and the system needing the protection remains at risk.
     
    Last edited: Sep 12, 2013
  11. WBahn

    Moderator

    Mar 31, 2012
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    I think he is thinking about how, to get the same power, if you have something running at a lower voltage you need higher amperage.
     
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