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Fuse question

Discussion in 'Electronic Repair' started by Golf, Jan 2, 2006.

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  1. Golf

    Golf Guest

    I have a Sony TV that has a blown fuse, 2.5amp, 250V. Can I replace
    with a 2.5amp - 125V fuse? I don't know why some TV' s have 250V fuses,
    and some have 125V fuses. Thanks group.
     
  2. Set Square

    Set Square Guest

    In an earlier contribution to this discussion,

    Probably because a large part of the world uses a supply voltage in the
    region of 250v!
     
  3. James Sweet

    James Sweet Guest


    If you have a 120v mains supply and the fuse is on the AC side of the
    rectifier then yes, that should be fine.
     
  4. Eric

    Eric Guest

    yes a lot of people don't get Voltage rating on fuses

    e.g. It would be pointless to put a 125 Volt fuse in a 3KV microwave line to
    the magnetron as when the fuse "fused" the Voltage would jump the gap, so
    you would need a 3KV fuse or greater

    so another words the Voltage rating is not imported until the fuse blown,
    then the fuse must stop the Voltage arcing the gap


    I have a Sony TV that has a blown fuse, 2.5amp, 250V. Can I replace
    with a 2.5amp - 125V fuse? I don't know why some TV' s have 250V fuses,
    and some have 125V fuses. Thanks group.
     
  5. Smitty Two

    Smitty Two Guest


    That sounds reasonable, but I'm confused. If I've got two fuses that are
    both the same physical size, and one is 125 volts and the other is 250
    volts, the gap from end cap to end cap (when the fuse blows) is the
    same. (And that gap is far in excess of what either of those voltages
    will jump.)
     
  6. Dave D

    Dave D Guest

    But fuses only blow like that when they encounter a severe fault condition,
    ie the appliance presenting a short circuit to the mains supply, which
    vapourises the entire fuse wire. Sometimes the fuse wire will simply fail at
    its weakest point leaving a small gap, which must be wide enough to prevent
    an arc.

    Dave
     
  7. mc

    mc Guest

    so another words the Voltage rating is not imported until the fuse blown,
    They may just have been through different testing and certification
    processes at the manufacturer.
     
  8. Probably, though keep in mind that high current arcs can do jump much larger
    gaps than you might think, especially when mixed with a little metal vapor...

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  9. Mike Berger

    Mike Berger Guest

    Yes, but first you should find the reason that the fuse blew,
    before more damage occurs.
     
  10. mc

    mc Guest

    Yes, and as someone pointed out, they may behave differently (producing
    different size gaps) when they blow gently under minor overload.
     
  11. Ray L. Volts

    Ray L. Volts Guest

    More on fuse ratings:

    http://www.lnl.com/howto/fuse.htm
     
  12. Smitty Two

    Smitty Two Guest

    Using "suppose" numbers, are you saying that a fuse manufacturer can
    actually make a 250 volt fuse that will burn a 1/4" length of filament
    and a 125 volt fuse that will burn a 1/8" length of filament? Reliably
    and repeatedly?

    If we're talking about standard 1/4" x 1 1/4" or 5 mm x 20 mm fuses, I
    say there's no damn difference between a 250 and a 125 with the
    exception of the lettering on the cap.

    Now, if anyone can give me real information to the contrary, I'll
    happily concede, but so far I haven't seen anything that I'd consider
    more than speculation.
     
  13. Ross Herbert

    Ross Herbert Guest

    This is the good guts: From http://www.lnl.com/howto/fuse.htm (some
    minor editing included.

    QUOTE
    VOLTAGE RATING: The voltage rating, as marked on a fuse indicates the
    fuse can be relied upon to safely interrupt its rated short circuit
    current. in a circuit where the voltage is equal to, or less than its
    rated voltage.

    The standard voltage ratings used by fuse manufacturers for most small
    dimension and midget fuses are 32, 125, 250 and 600.

    Fuses are sensitive to changes in current, not voltage maintaining
    their "status-quo" at any voltage from zero to maximum rating. It is
    not until the fuse wire reaches melting temperature and arcing occurs
    that the circuit voltage and available power influence the fuse
    performance and determine the safe interruption of the circuit.

    To summarize, a fuse may be used at any voltage less than its voltage
    rating without detriment to its fusing characteristics, but may also
    be used at voltages higher than its certified voltage rating if the
    maximum power level available at the fuse under a "dead short"
    condition can only produce a low energy level non-destructive arc.
    ENDQUOTE

    Note that any power source supplying the load via the fuse must not be
    able to sustain an arc into a short circuit via the blown fuse. As
    long as this criteria is observed a low voltage fuse (eg, 125V AC) can
    be used in a circuit supplied from 250V AC, or even more.

    From page 150 of SWE-CHECK's Fuse Bible
    http://www.swecheck.com.au/frames/product_catalogue_index.html

    Interrupting Rating (Breaking Capacity)

    Also known as the breaking capacity or short circuit
    rating - is the maximum approved current which the fuse
    can safely interrupt at rated voltage. During a fault or
    short circuit condition, a fuse may receive an
    instantaneous overload current many times greater
    than its normal operating current. Safe operation
    requires that the fuse remain intact (No explosion or
    body rupture) and clear the circuit.
    LBC = Low Breaking Capacity
    HRC =High Breaking Capacity
    EBC = Enhanced Breaking Capacity.
     
  14. Asimov

    Asimov Guest

    "Smitty Two" bravely wrote to "All" (03 Jan 06 21:10:49)
    --- on the heady topic of "Re: Fuse question"

    ST> From: Smitty Two <>
    ST> Xref: core-easynews sci.electronics.repair:353870

    ST> Using "suppose" numbers, are you saying that a fuse manufacturer can
    ST> actually make a 250 volt fuse that will burn a 1/4" length of filament
    ST> and a 125 volt fuse that will burn a 1/8" length of filament? Reliably
    ST> and repeatedly?

    ST> If we're talking about standard 1/4" x 1 1/4" or 5 mm x 20 mm fuses, I
    ST> say there's no damn difference between a 250 and a 125 with the
    ST> exception of the lettering on the cap.

    ST> Now, if anyone can give me real information to the contrary, I'll
    ST> happily concede, but so far I haven't seen anything that I'd consider
    ST> more than speculation.

    Perhaps a 125 volt fuse is made with the same wire as the 250 volt
    fuse. However the 250 has been approved at 250 and the 125 passed the
    125 testing. So if there is an economy in making a 125 rated fuse over
    a 250 rated one then I wouldn't risk using a 125 fuse in a 250 spec'd
    circuit. (if made from the same spool of wire, we don't know for sure)
    However, the wire may not be the only story. Remember that the package
    is part of the fuse. Thus perhaps the thickness of the glass tube
    also is a function of the safety rating for the 250 and 125 spec too.
    Recall there is 4 times more energy involved between 125 and 250!

    A*s*i*m*o*v

    .... Thomas Edison invented the "Light Emitting Resistor"
     
  15. Dave D

    Dave D Guest

    Read Ross Herbert's post, that's all I need to say on the subject. Perhaps
    next time you might keep it civil rather than jumping on people and making a
    dick of yourself.

    Dave
     
  16. Smitty Two

    Smitty Two Guest

    Wow dude, I'm being as civil as possible, don't know what you read into
    my post that isn't there. Or do you consider skepticism rude? Sorry I
    hate the smily emoticons and stupid <g> things, but I'm not jumping on
    anyone, including you.

    Now, Ross Herbert's post SUBSTANTIATES my contention. Have you actually
    read and comprehended this entire thread, or did you just take offense
    to my use of the word "damn.?"
     
  17. Dave D

    Dave D Guest

    I did read the post as being rather hostile TBH. However, I withdraw my
    comments and offer my apologies, you say there was no intended hostility and
    I accept that.

    No hard feelings I hope!

    Dave
     
  18. Smitty Two

    Smitty Two Guest

    No sweat Dave, thank you. I do understand that the tone of written words
    can be easily misconstrued. I'm as irritated by uncouth behavior on
    usenet as you are.

    Jon
     
  19. spudnuty

    spudnuty Guest

    Maybe the confusion here is that the OP was talking about AC fuses. DC
    is a whole different story esp. in free air. The physics lab where I
    worked for a while had a 100 VDC supply 100 amps available. I was
    designing a reversing switch for an inductive load and drew an arc that
    completely ate the relay in the test cell. Turned it into a puddle of
    molten metal and plastic, walked out the power leads and snapped off.
    Talking to engineers at the local transit system they were very
    familiar with this. "We just walk away".
    Richard
     
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