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Fuse explosion - as a warning

TechEkspert 6411 33

TL;DR

  • Looks at the explosion risk of 3.15A fuses when short-circuit current gets too high, using several fuses from different sources and types.
  • Shows a mains-installation short circuit where the fuse wire burns through, the tube breaks, and the glass shards explode.
  • Advises eye protection when repairing equipment because glass fuses can burst violently during fault conditions.
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  • Shattered fuse with scattered glass material on a white background.
    When I posted a short piece on fusible links, I got a hint from @398216 Usunięty that it was worth raising the subject of the risk of a fuse exploding when the short circuit current is too high . I have collected several fuses from various places 3.15A of various types. In the material you will see the moment they burn out during a short circuit in the mains installation. In the glass case, you can see the moment when the wire burns through, the tube breaks and then the glass shards explode. It is advisable to use eye protection when repairing various types of equipment.



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  • #2 21026600
    rosomak19
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    I once had an explosion of a capacitor straight in the face : / Not to mention the pyrotechnic effects that occurred afterwards, I was setting the rest current in my DIY power amplifier, powered by 1.5 kVA taf, and the meter probe slipped out and went to the best place, that is between the leads of the power transistor. I've never experienced such a thing, and out of all this instead of pressing the power switch, I tore the plug out of the socket, the resistors were blown out like candles on a cake because they lit up XD . Well we had to do the board from scratch because it blew out , and order parts . I had to ventilate the room for a few hours, and I could still smell burning for a few days.
  • #3 21026610
    kortyleski
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    There happened to be an uncontrolled shorting of a set of 0.17F capacitors charged to 120V. The bang and flash is quite impressive, I smoked a cigarette with very trembling hands. Metal droplets from a screwdriver what fell between the rails melted into the safety goggles. It is therefore always good practice to wear goggles and gloves when working with considerable energies.
  • #4 21026715
    Grzegorz_madera
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    There is such a parameter of a fuse as the breaking capacity. It tells you the maximum current it can disconnect without melting or exploding the case. Littelfuse makes fuses with a breaking capacity of between 35A and 1500A, some have this specified at 4-10xIn. This also depends on the interrupting voltage of the current. The Littelfuse mentioned in one model, for example, specifies 10000A at 125V, while at 250V it is only 40A.
  • #5 21026775
    123104
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    Something like this happened to me. I accidentally applied 220V to the TG2 transistor (green) (I touched the wrong place with the wire). It banged like a shot from a KBKS and a hole a few mm deep appeared in the ceiling. The green cap flew like a bullet, fortunately not at me but upwards.
  • #6 21026776
    TechEkspert
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    Thanks for the feedback, at high energies indeed many components can explode, not only the fuse, diode or transistor but also mechanical switching elements can wreak considerable havoc.

    I am puzzled by the mechanism of destruction of the glass fuse,
    first you can see the flash of the burnt wire,
    after a while you can see the formation of cracks on the entire surface of the tube,
    at the end fragments of glass fly throughout the frame.

    Is it a heat wave that reaches the glass, causes stress and then the heated gas bursts the tube?

    I think you can also see the deposition of metal vapour on the tube.
    Sometimes I came across fuses that were not burst but were covered on the inside with a layer of metal.
  • #7 21026802
    m2606
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    TechEkspert wrote:
    Sometimes I have come across fuses that were not blown but were covered on the inside with a layer of metal.
    I in the army accidentally put a buzzer from razor blades on the interphase. The water disappeared together with the cup and the razor blades.The shells looked from the inside just like the inside of the fuse.It was probably the biggest "burn".
    Well, except maybe the key 17 of which was left only "stick",fortunately I had gloves.
    Frequently I removed the 5w bulbs from cars. They were working, but it was almost impossible to see that they were lit.
  • #8 21026812
    Grzegorz_madera
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    TechEkspert wrote:
    I think you can also see the metal vapour deposition on the tube.
    When a large current is switched off, the metal from the wire vaporises and deposits on the glass, and this causes a voltage breakdown and current flow over the glass. This is likely to cause heating and cracking of the glass. This situation does not occur with a sand-filled fuse.
  • #9 21026920
    398216 Usunięty
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    Let me add one more comment to the last words of the Author's statement in the video - There is a reason why silica sand fuses are used in some PU equipment power supplies. When replacing it with an ordinary one, not only do you risk getting injured by glass fragments, but you may also contribute to more damage than you would by using a fuse with silica sand that extinguishes (and therefore shortens the duration of supply to the - perhaps not yet fully damaged - circuit). A longer duration of supply is more likely to cause further damage.
  • #10 21027027
    TechEkspert
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    What is PU equipment?

    Sometimes I have also come across ultrafast (aR) fuses, but how their design differed from fast ones I have not been able to check.
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  • #11 21027038
    398216 Usunięty
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    TechEkspert wrote:
    What is PU equipment?
    Equipment P common U use -. means domestic... ;) (I didn't make that up).
  • #12 21027306
    prosiak_wej
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    Eye protection when running anything with higher power is an absolute must. Plus a dedicated circuit in the workshop with its own differential and a B16 overcurrent, so that in the event of a malfunction, only this circuit is switched off and not the whole room as in the case of famous jutubers ;) .
  • #13 21027394
    ArturAVS
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    @TechEkspert What if you did a similar demonstration but for DC? And compared? This would show experimentally the differences between AC and DC and what the problem with DC arc extinguishing is. By the way, the biggest fuses I've been able to "plant" were the 630A BMs in the plant switchgear. A 19 gauge spanner fell out of my overalls pocket and short-circuited the drain rails, the bang in the RG room was like a practice grenade at least. Even the typical solid construction of the BM along with the sand filling did not save it from being blown apart. It was a good thing that I was standing on the scaffolding at this point because fragments of torn ceramics are sometimes sharper than glass.
  • #14 21027405
    barondary
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    I had a neon light explode because I didn't give a resistor and connected directly to 230V. It just exploded! The glass shattered into tiny pieces and it's a miracle it didn't hit my eye. Now I wear corrective glasses anyway so I feel safer.
  • #15 21027447
    TechEkspert
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    I was thinking of DC testing however I don't have a suitable capacitor bank, DC is quite a dangerous game, you would also need a switch that can withstand a few of these switching on and to check what voltage is left on the capacitors.

    Here from the 8th minute of the test with DC and fuses, the author has built a varistor tester and also checks other components how they react to short-circuit tests on DC:



    .
  • #16 21027468
    ArturAVS
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    I was thinking of a simple circuit; Bridge->capacitor->two series connected kettles in the role of current limiter (and forcing it)->serial tested patient (fuse).
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  • #17 21027503
    TechEkspert
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    The kettle would have to limit the capacitor charging current?
    If the bridge were to participate in the short-circuit current then it would have to be powerful.

    I see that the GDTs stand up well to DC testing:


    .
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  • #18 21027510
    ArturAVS
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    TechEkspert wrote:
    The kettle would limit the charging current of the capacitors?
    No, although it can be done that way. I was referring to forcing the current to flow but so that it would not be a short circuit.
  • #19 21027802
    398216 Usunięty
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    ArturAVS wrote:
    the largest fuses I was able to "plant" were BMy 630A in the company switchboard
    a colleague was replacing a live switchboard (because the ZE was only due to arrive in a week's time to disconnect the transformer substation) and a pair of pliers slipped out of his hand while he was putting in a new one (still on the resotex ). They fell on the phase-to-phase terminals and evaporated. Admittedly, the colleague covered himself with his hand at the last moment, but still half his face was burnt. He was laid off for a month and had to grow a beard to hide the scars.
  • #20 21028045
    ArturAVS
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    I wasn't doing any electrical work in this case, I was setting up scaffolding for painting and installing cable trays for the new RG lighting installation. There was a mains socket in one cell in the distribution board and I had an extension cord plugged in there for the drill, so the door was open too. The spanner fell and bounced off the scaffolding and by some miracle hit the gap in the Plexiglas cover on the drain rails (less than a centimetre). Apart from the balls of steel embedded in the casing, its larger components I could not find.
  • #21 21032218
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    I wonder how it is possible that a large ceramic BM can explode like a fragmentation grenade,
    I understand a small glass fuse, but the BM insert has a housing of considerable thickness, the whole is covered with sand.

    Is it also works on the principle: the larger the insert -> the greater the short circuit current and as a result the small glass one will explode at 100A and such a BM at 100kA.

    I also heard about the fuses on the DC buses in the old switchboards (I don't remember if Strowger or Pentaconta) and a lot of caution when replacing them because with the capacity of the DC power plant and the short-circuit current of the batteries, sometimes such a fuse would explode when a short circuit occurred again.
  • #22 21037568
    jarekgol
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    It may have already been there, but it's cool



    I've also seen quite a few glass ones with the metal vaporised on the inside.
    And as for BMs I think bigger fuse, bigger problems ;) After all, the idea of any fuse is that it's supposed to melt, and just melting as we know doesn't immediately break the circuit. Then the arc burns there, and in "thicker" circuits it will also be thicker.
    Fused balls of metal in the eyes I have unfortunately also processed, but with electrics, not electronics.
    Well, in some devices they put rubber condoms on these 5x20 PCB mounts. This reduces the risk of touching and limits shrapnel.
    My dad repairs flashes and studio lights and there various things like to explode and arc across the board.
  • #23 21037640
    ArturAVS
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    Here a nice attempt at blowing a 5000A fuse;




    Fine capacitor bank :D .
  • #24 21037643
    398216 Usunięty
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    However, a flashlight or a strobe is a slightly different kind of circuit - admittedly, the voltage is high (I'm talking about the power supply of the burner - the voltage of its triggering/ionisation is several kV at least), but the current is relatively small. The fact is that it is actually very simple to burn a path on the laminate - backwards the thickness of the path is only a few tens of MIKROMETERS.
    Every audio service technician has probably at least once encountered damage to the paths in a power amplifier - the voltages there are in most cases several tens of volts and the current (fuse protection) rarely exceeds 5A (at least in home audio).
  • #25 21038506
    jarekgol
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    398216 Usunięty wrote:
    the thickness of the path is only a few tens of MIKROMETERS.
    It's fun to bump this up with electricians and wire cross-section selection :) Another interesting thing is the reported current of the mosfets and the thickness of their feet (I mean THT)
  • #26 21038554
    prosiak_wej
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    And the thickness of the wires that, inside the transistor housing, connect its legs to the structure?
  • #27 21053746
    web69
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    Many years ago I was replacing a DC 2500A 48V powerhouse, at the same time the rooms were being renovated. The rails from the battery room were going under the ceiling, a painter on a ladder decided to put a bucket of paint down just on these rails. When I said that this was a bad idea and there was 48V here, the farmer replied that he was doing it by force and nothing happened. The bang was so powerful that it rang in my ears for a week, the painter on the floor with the rest of the bucket in his hand and everything in the paint. The telephone exchange didn't even register the fault, the fuses on the 2x1200A battery didn't let go
  • #28 21054210
    TechEkspert
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    He must have been surprised when the bucket disappeared, such a bucket should allow current to flow triggering the fuse but perhaps the contact was insecure and the amount of heat generated at the contact between bucket and rail and as current flowed through the bucket disconnected the circuit faster than the fuse?

    Maybe the electromagnetic field made it easier to push the bucket out? (similar to the railgun).
  • #29 21054522
    web69
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    A bucket of about 5-7L of thinset, a 24x opzs 2500Ah battery, what's that 500 or 700A current.... bucket gone, a peasant in paint lying on the ground and 20 people roaring with laughter. In such facilities the work was most often on a living organism and I was no longer laughing when connecting a 230V guaranteed inverter where I mistook the - for earth and as telecoms equipment has a + on earth, the ring ends of the 25mm cable evaporated in my hands. Gloves saved my fingers, goggles shielded my eyes and there was no problem with defecation either (pun intended)
  • #30 21054574
    m2606
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    Let the peasant be happy that the paint was not flammable.
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    Topic summary

    ✨ The discussion centers around the risks associated with fuse explosions during short circuits, highlighting the importance of safety measures such as wearing eye protection. Users share personal experiences of component failures, including capacitors and transistors, leading to explosive incidents. The breaking capacity of fuses is emphasized, with Littelfuse mentioned as a manufacturer providing fuses with varying breaking capacities. The mechanism of glass fuse destruction is explored, noting that metal vaporization can lead to voltage breakdown and glass cracking. The advantages of sand-filled fuses over glass fuses in preventing injuries and minimizing damage during failures are also discussed. Additionally, the conversation touches on the dangers of working with DC circuits and the need for proper equipment and precautions.
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    FAQ

    TL;DR: A 3.15A glass fuse can still explode during a mains short because fault current can far exceed its safe interrupting limit, and one expert warned that sand-filled fuses "extinguish" the arc faster. This FAQ is for repairers and hobbyists who need to prevent shard injuries, arc damage, and avoidable equipment loss during fuse faults. [#21026920]

    Why it matters: A fuse rating in amps alone does not tell you whether the fuse will survive a real short circuit without spraying glass, metal vapor, or ceramic fragments.

    Fuse / setup Construction mentioned in thread Behavior under high fault current Practical consequence
    Ordinary 3.15A glass fuse Glass tube, visible fusible wire Wire burns, glass cracks, shards can fly Eye-injury risk during mains faults
    Sand-filled fuse Filler identified as silica/quartz sand Better arc extinction, less surface flashover Limits damage duration and fragmentation
    Large ceramic BM fuse Thick ceramic body with sand filling Can still burst under very severe faults Ceramic fragments can be sharper than glass

    Key insight: Choose a fuse by breaking capacity and construction, not just current rating. In the thread, both small glass fuses and large sand-filled BM links failed violently when the available fault energy was high enough. [#21026715]

    Quick Facts

    • Littelfuse fuse breaking capacity was quoted in the thread as 35A to 1500A, with one example rated 10000A at 125V but only 40A at 250V. That shows why voltage rating changes real interruption performance. [#21026715]
    • A reported capacitor accident involved 0.17F charged to 120V; molten metal from a dropped screwdriver fused into safety goggles. That is a direct PPE case for face and eye protection. [#21026610]
    • One workshop-protection idea was a dedicated branch with its own RCD and B16 overcurrent breaker, so a project fault trips only that circuit instead of blacking out the whole room. [#21027306]
    • Extreme DC systems in the thread included 48V / 2500A power plants, 2x1200A battery fuses, and a 24-cell OPzS 2500Ah battery set. Even at low voltage, short-circuit energy was described as explosive. [#21053746]
    • Large-fault examples included 630A BM fuse links in switchgear and 400–600A BM links in a harbor LV installation; both produced blast, dust, and flying fragments despite sand filling. [#21027394]

    Why can a 3.15A glass fuse explode and throw shards during a mains short circuit instead of just melting safely?

    A 3.15A glass fuse can explode because the short-circuit current from the mains can be far above what its body can interrupt safely. In the thread video, the wire first burned open, then cracks spread across the glass tube, and finally shards flew outward. Another participant explained that large fault current vaporizes metal and sustains an arc, which heats the tube instead of ending cleanly. The ampere rating only states normal current; it does not guarantee safe interruption under every fault level. [#21026812]

    What is the breaking capacity of a fuse, and how do voltage and fault current affect it in models like Littelfuse fuses?

    Breaking capacity is the maximum fault current a fuse can interrupt without the body melting apart or exploding. One thread example cited Littelfuse parts rated from 35A to 1500A, and one model was quoted at 10000A at 125V but only 40A at 250V. That means the same fuse family can tolerate very different fault conditions depending on voltage. Higher voltage makes arc extinction harder, so safe interrupting current can drop sharply. [#21026715]

    How do sand-filled fuses compare with ordinary glass fuses when interrupting high short-circuit currents?

    Sand-filled fuses handle high short-circuit currents more safely because the silica or quartz filling helps quench the arc and shorten current flow. A thread participant warned that replacing such a fuse with an ordinary glass type can increase injury risk from flying glass and can also worsen equipment damage because the arc lasts longer. Another reply added that the metal-vapor flashover seen on glass does not occur in a sand-filled fuse. That makes sand-filled designs the safer choice where fault energy is high. [#21026920]

    What causes metal vapor to deposit on the inside of a blown glass fuse, and how can that lead to cracking or flashover over the glass surface?

    Metal vapor deposits on the inside of a blown glass fuse when heavy current vaporizes the fusible wire during interruption. One reply explained that this conductive coating can let voltage break down across the inside surface, so current then tracks over the glass itself. That extra surface current heats the tube and can crack it. In the thread, users also reported many failed glass fuses with a clear metal coating inside after the event. [#21026812]

    What is PU equipment in the context of fuse selection and household power supplies?

    PU equipment means ordinary household or domestic equipment in this thread’s terminology. A participant explicitly clarified that it stands for common-use equipment and refers to domestic gear and power supplies. In context, the term was used while explaining why some household power supplies use silica-sand fuses instead of ordinary glass ones. That matters because home equipment can still see fault conditions severe enough to justify better arc extinction. [#21027038]

    How do ultrafast aR fuses differ from standard fast-blow fuses in construction and application?

    The thread only states that ultrafast aR fuses exist and are distinct from ordinary fast fuses, but it does not describe their internal construction. The author said he had encountered aR fuses and had not been able to verify how their design differed from fast ones. So the only safe conclusion from this discussion is application-level: users recognize them as a separate fuse category used where faster fault interruption matters. The thread provides no verified geometry, filler, or timing data beyond that. [#21027027]

    What safety gear should I use when testing or repairing high-energy circuits so I’m protected from exploding fuses, capacitors, and ceramic fragments?

    Use eye protection first, then gloves, and add face and body protection when fault energy is high. The thread includes reports of molten metal embedded in safety goggles, ceramic BM fragments described as sharper than glass, and a user who later refused to open LV switchgear without a mask, gloves, dielectric boots, and protective clothing. One practical rule from the discussion is simple: if the circuit stores or can deliver significant energy, treat blast and shrapnel as credible hazards, not edge cases. [#21054845]

    How should I set up a dedicated workshop circuit with its own RCD and B16 breaker to limit damage when an electronics project fails?

    Set up one separate workshop branch so only that branch trips when a project fails. 1. Put the bench outlets on a dedicated circuit. 2. Protect it with its own RCD and a B16 breaker. 3. Keep experimental loads on that branch, not on the room’s general outlets. The thread recommendation aimed to stop a fault from cutting power to the entire room. It is a containment strategy, not a substitute for proper PPE or correct fuse selection. [#21027306]

    What are the main differences between AC and DC fuse testing, especially when it comes to arc extinction and danger level?

    DC fuse testing is more dangerous because extinguishing a DC arc is harder once current starts flowing. In the thread, one user proposed an AC-versus-DC comparison specifically to show the arc-extinction problem, and the author replied that DC is “quite a dangerous game” and requires a suitable capacitor bank, a switch that survives several operations, and checks for leftover capacitor voltage. AC naturally passes through zero crossings; DC does not, so the test setup becomes much less forgiving. [#21027447]

    How could I build a simple DC fuse test setup using a bridge rectifier, capacitor, and kettles as a current limiter, and what are the main risks?

    One proposed setup was bridge rectifier -> capacitor -> two series kettles as current limiter -> tested fuse in series. The aim was to force current without making a dead short. The author immediately pointed out two main risks: the kettles may have to limit capacitor charging current, and the bridge would need to withstand part of the fault current, so it must be powerful. Residual capacitor voltage after the test is another stated hazard. This idea is experimental and was discussed as risky even before construction details were settled. [#21027503]

    Why can even a large ceramic BM fuse filled with кварtz sand still burst apart under a severe fault current?

    A large ceramic BM fuse can still burst because high fault energy can exceed what even a sand-filled body can absorb and interrupt cleanly. The thread describes 630A BM links blown apart in switchgear and 400–600A BM links rupturing so violently that quartz dust filled the room. Sand helps quench the arc, but it does not make the fuse indestructible. As one comment put it, bigger fuses can mean bigger problems because the arc in a “thicker” circuit is also more severe. [#21054845]

    What is a GDT, and why does it reportedly survive DC short-circuit testing better than some other protection components?

    “GDT” is a protection component that conducts during an overvoltage event, using a gas discharge path as its key operating element. In the thread, the author said GDTs “stand up well” to DC testing and linked to a demonstration, but he did not provide measured current, voltage, or survival limits in the posts themselves. So the thread supports only a narrow claim: compared with some other tested parts, GDTs were observed to tolerate DC short-circuit-style tests better in that example. [#21027503]

    How dangerous are battery-backed DC systems like 48V telecom power plants, UPS strings, or large VRLA banks during a short circuit?

    They are extremely dangerous because low voltage does not mean low energy. The thread cites a 48V, 2500A power plant, 2x1200A battery fuses that did not clear during one event, and a 24-cell OPzS 2500Ah battery string. Users described disappearing metal objects, ringing ears for a week, evaporated cable lugs, and explosive splatter from vaporized metal. Another post warned that DC battery strings also raise shock concerns at higher series voltages, alongside the blast hazard from short circuits. [#21054522]

    Why do some telecom and radio systems use positive ground or connect the + supply to the chassis, and what practical advantages does that have?

    The thread says some telecom and radio systems use positive ground because that arrangement is less sensitive to interference and emits less interference. One participant also stated that older vehicles with positive ground corroded less and suffered less electro-erosion at electrical contacts. The same discussion notes that this convention survives in some licensed-band radio equipment, where the positive supply remains bonded to the chassis. The thread does not add measured EMC figures, but it clearly presents noise reduction and corrosion behavior as the practical advantages. [#21056397]

    What protective covers or fuse holders for 5x20 PCB fuses help reduce the risk of shrapnel and accidental contact in electronic devices?

    The thread mentions rubber protective sleeves fitted over some 5x20 PCB fuse mounts. One participant noted that these covers reduce the risk of accidental touch and also limit shrapnel if the fuse ruptures. That makes them a simple secondary barrier around a fragile glass fuse. They do not replace correct fuse selection, but they can reduce injury and contamination inside the device when a small fuse fails violently. [#21037568]
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