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Fuse question

Discussion in 'Electronic Basics' started by Harry Muscle, Dec 18, 2003.

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  1. Harry Muscle

    Harry Muscle Guest

    If I want a fuse to blow at 2A, what size do I need to buy? I'm assuming
    fuses have a little bit of safety, so that a 2A fuse won't blow till say
    2.5A ... hence my question ... if I want a fuse to actually blow at 2A, what
    rating do I get?

  2. 2A. The only safety there is is whether it's slow-blow or fast blow. I
    think that's probably where your confusion is coming from.

  3. Harry Muscle

    Harry Muscle Guest

    How slow or how fast are we usually talking? Any standard recommendations
    when it comes to installing a fu from of a transformer? It's rated at
    250VA, but I don't every expect to reach more than 150VA.

  4. The point of a slow blow fuse is to allow temporary current overages, such
    as when a motor starts. A fast blow fuse will blow instantly.

  5. Ross Mac

    Ross Mac Guest

    A good rule of thumb is motors, heaters and transformers use slow blow and
    semicondutors use fast blow. This is an oversimplification, but I think
    that's all you are asking at this point.....good luck....Ross
  6. The fuse current rating is normally the largest current that is
    guaranteed not blow the fuse under some specified ambient temperature
    for some rather long (specified) period of time. Usually some
    specific overload is required to guarantee opening in some specified
    period of time. A common one is 10 seconds or less with a 100%
    overload from a cold start. If the fuse is operated for long enough
    at rated current for it to reach thermal equilibrium, the opening time
    is significantly shortened. You need the actual fuse data sheet to
    nail down any specific example.

    A fuse is not generally a precision current limiting device, but a
    rough protection that limits the spread of damage in the event of a
    severe overload.
  7. David Wood

    David Wood Guest

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