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Ballotini Fuses

Discussion in 'Electrical Engineering' started by Pilgarlick, Apr 22, 2005.

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  1. Pilgarlick

    Pilgarlick Guest

    Hello All

    I have just replaced a failed bulb with a similar one of the candle type and
    noticed on the package of the new bulb that it was Ballotini Fused. In spite
    of working in the power industry for nearly thirty years I have never
    encountered this item before. Can anyone give me the low down on the
    technical meaning of this phrase and also an explanation of why such an item
    may be necessary in a humble 240v 15w tungsten filament candle bulb?

    Thank you in anticipation of lightening my darkness (pun intended)



  2. "Me too". I've never seen this before either. A Google search on
    "Ballotini" and "Fuse" turned up references to glass beads. Even
    consulting the erratic wisdom of turned up nothing.
    I've never seen this statement on decorative lamps I've purchased in

    I do know that some lamps have a fusible element built into them to
    prevent trouble if the lamp develops an internal short; though it may be
    unlikely, sometimes vibration (or a manufacturing defect) will allow the
    lamp filament leads or supports to touch and short out. The lamp's
    built-in fuse I guess saves having to replace the branch circuit fuse
    (or reset the branch breaker) - you'd rather have one lamp go out over
    the dining room table than find your way in darkness to the household

  3. Pilgarlick

    Pilgarlick Guest

    Thanks very much for the reply. I also did the Google search with the same
    result, though it did turn up a large page of what seemed to be standard
    legal disclaimers which had some reference to Ballotini ( I couldn't be
    bothered to read it all - it was a large tightly written page - aren't all
    legal things).

    Your comments about the internal fault protection sound as if they hold
    water and are totally reasonable, so I think I'll run with that one for the
    time being.

    Thanks for the reply.

    Best wishes from the UK

  4. Try the manufacturer and let us all know

  5. Dave D

    Dave D Guest

    I must say I've never seen that happen, and I'd say it's virtually
    impossible given the spacing on 240V bulbs.

    What happens very frequently IME is the element itself breaks down
    (expansion/contraction causing distortion) to a point where the coils short
    out to one another causing a low resistance. This usually causes a bright
    blue flash and trips a breaker. A real PITA is when it happens to a bulb
    connected through a dimmer and it takes out the triac.

    I would say about 75% of my household bulbs have tripped the breaker when
    they failed, and on examining them there's been no obvious shorts other than
    rather poorly-looking filament.

    I recently had a mains halogen bulb fail, which have very fine and
    close-wound filaments. Naturally when it failed it took out the dimmer and
    tripped the breaker and lit the room like a strobe light!

  6. Ballotini are tiny glass spheres, often used in reflective paint
    used on road surfaces. However, they are also used inside fuses
    where they help quench the arc, hence more rapidly interrupting
    the current flow when the fuse blows.
    The problem is that the lamp can flash-over internally when the
    filament breaks. The mechanism is that as the filament breaks,
    a small spark jumps the gap. This forms a plasma through which
    the current continues to flow. The plasma has a lower impedance
    than the filamant, so it grows in length, with the two ends of
    the arc running in opposite directions up the filamant until it
    reaches the lead-in wires. Now you have an unballasted discharge
    lamp, whose current draw is limited only by the supply impedance;
    this is basically a short circuit. This all happens in the order
    if a millisecond, and may be familiar to you as a flash and pop
    sound which sometimes happens when a lamp dies.

    I would speculate this is probably more common on 240V supplies
    than on 120V supplies, but I have no evidence to back that up.
  7. Dave D

    Dave D Guest

    Yes, the 240V incandescent types sold here in the UK tend to have them as
    well, but typically they don't blow fast enough to stop the breaker
    tripping! Aren't fuses marvellous!

  8. daestrom

    daestrom Guest

    This sounds a bit like the old 'silver-sand' fuses we used to use. A sliver
    fusible link, but the cartridge filled with a fine silica sand. When the
    fuse blows, the arc melts the sand forming a glass 'slug' that interrupts
    the arc. Gives remarkably high interrupting rating in a small package.

    FWIW, a friend in the training department at work maintains all the overhead
    projectors used in the class rooms. These are modern digital projectors
    with a 'timer' for lamp life. When the lamp life timer reaches 1500 hours,
    it shuts off the lamp regardless of light output. These bulbs *look*
    incandescent in nature, but are some exotic version that cost $450 a piece.

    Because of their high cost, my friend decided to just reset the timer on one
    once and 'run till failure' of the bulb. Got an extra 300 hours, but the
    'failure' was catastrophic. Bulb shattered while in use and filled the
    inside of the projector with glass from the envelope and blew out the
    circuit board that powers the bulb. (i.e. there was a *good* reason for the

    Anyway, sometimes when he replaces the bulbs that have reached their timer
    limit (he never again 'just reset the timer' ;-) the glass envelope around
    the bulb shows signs of melting and drooping. Apparently as the inside
    surface gets coated with evaporated filement material, they get much hotter
    (and light output diminishes).

  9. Pilgarlick

    Pilgarlick Guest

    The enquiry was politely and expansively explained by various contributors
    and I can well do without uninformative smart-ass comments such as yours, as
    can all newsgroups. When you have nothing to say then say nothing.

  10. Dave D

    Dave D Guest

    They're usually metal halide IIRC, ie discharge bulbs with no filament. The
    prices charged for spare projector bulbs are extortionate IMO, and when
    choosing a brand it's wise to check the price of spare bulbs as they do vary

    The timer isn't just there to prevent catastrophic failure, apparently the
    brightness diminishes and the colour temperature of the bulb shifts to an
    unpleasant yellow at the end of its life which adversely affects the image

  11. keith

    keith Guest

    I've not had a filament take out a CB in a *long* time (nor a dimmer, in
    fact). I have a bunch of 300W and 500W halogens, as well as a housefull of
    smaller ones. As slow as fuses are, CBs are slower.
  12. Depends which country you are in and on your supply impedance.
    The magnetic (fault current) element of EU MCB's is significantly
    faster than fuses used in electricity supply (unless your supply
    impedance is too high such that the prospective short circuit
    current is not high enough to trigger the MCB's magnetic element).
    If you are in a country with uses only thermal elements inside
    CB's, then a fuse is going to be faster.

    Halogens are less likely to flash over has the bulb operates at
    a much higher internal gas pressure and flashover just doesn't
    happen in the power ratings of lamps you find used at home.
    However, when higher power halogens do flashover, they explode.
  13. Current-limiting fuses aren't slow, they must clear within 1/2 cycle.
    But a fuse built into a lamp won't be a current-limiting type.

  14. I have seen miniature 120 V incandescent lamps short out and damage
    their driving circuitry quite regularly. I used to work at a steel mill
    where the scrap aisle crane scale used a score-board display composed of
    dozens of 6-watt lamps. Due to the heavy vibration and an unfortunate
    choice of lamp style, the filament support wires would touch and take
    out the triacs driving the lamp array.

    Now that's unusual in my experience. I've been swapping burnt lamp
    bulbs in my home for decades and not once have I had a breaker trip on a
    lamp failure. Could this be the one advantage of 120 V domestic wiring
    over 240 V? True, it does take us much longer to boil a kettle...

  15. This should be clearly visible in a lamp. I've taken apart many 120 V
    lamps in my school days (there was something about a 1000 watt clear
    mogul base lamp carefully eviscerated of all its internals and filled
    with water that delighted my childish mind) ; but never noticed a fuse
    Interesting - this momentary plasma explains the very bright flash I've
    noticed when a lamp burns out. My family is tired of hearing me
    complain that I might have saved that lamp if I'd only waited 1/120th of
    a second to switch it on.

  16. I'm pretty sure that whatever British Standard covers our GLS
    lamps, it must require fuses in the lamp base because all such
    lamps have them. The ballotini fuses are wire ended glass tubes,
    perhaps 10mm long and a few mm diameter in the lead-in wires,
    but not in the low pressure gas-fill part. Ballotini fuses are
    quite rare though -- normally it's simply done by having a
    thinned section of lead-in wire (again not in the low pressure
    gas-fill part). Fuses always seem to be fitted to both lead-in
    wires. They can be seen in the clear glass GLS lamps.

    I don't recall seeing fuses in 300W and upwards GES (mogul)
    lamps here either. (Yes, I took them apart too, and carefully
    cut round the neck to remove the pear shaped glass bulb.
    My school squash court used to use the 300W and 500W ones.)
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