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Fuse explosion - as a warning

TechEkspert 6369 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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  • #31 21054639
    TechEkspert
    Editor  
    Posts: 7047
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    Well that's right, that + on the ground in the control panels (or -48V power supply if you prefer) has always increased my attention. Interestingly, this power supply scheme has survived and radios for licensed bands still have the + power supply connected to the chassis.

    DC power supplies, but also smaller power supplies with batteries and even UPS and VRLA battery strings also increased my vigilance, the effects of a short circuit could be quite explosive and dangerous due to the temperature and splattering of evaporating metal. At higher voltages on the battery string you have to be careful with shock as DC can lead to electrolysis of the blood, the effects of which can show up in the days to come....
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  • #32 21054845
    Plumpi
    Heating systems specialist  
    Posts: 7888
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    Many years ago when I was working on an LV switchgear in the harbour due to a misconnection of a ship, it ruptured two 400 or 600A BMs on the substation. The bang was so powerful that, in spite of several doors being closed, all the workers converged to see what had happened.
    The switchgear became momentarily dark from the dust that arose due to the grinding and scattering of quartz sand with which the fuses were filled. After half an hour the dust settled covering everything with a perfect thin layer of fine dust. The clean-up was days later. My ears were ringing all day.

    From then on I never dared to open the cupboard again without first putting on a mask, gloves and dielectric boots and protective clothing. Previously, it happened to enter in a short T-shirt without a face mask :) .
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  • #33 21056350
    Matheu
    Level 25  
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    web69 wrote:
    telecom equipment has (+) on the ground
    TechEkspert wrote:
    power scheme survives and radios on licensed bands still have (+) power connected to the chassis.

    Does this (+) on the ground on the device chassis:
    1) have any substantive justification?
    2) was it simply- once done like that, and then other devices by necessity had to have it too, so that they could work with the previous ones ?
  • #34 21056397
    web69
    Level 33  
    Posts: 2143
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    Yes, this is because the true direction of current flow is from - to + . Equipment with + on the ground is less sensitive to interference and emits less of it. It used to be that most vehicles had + on the ground, they corroded much less and the electrical connections did not electro-erode as in modern vehicles
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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 glass fuse can rupture and spray shards when short-circuit current exceeds its 35–1500 A breaking capacity [Elektroda, Grzegorz_madera, post #21026715] “Wear goggles and gloves when working with considerable energies” [Elektroda, kortyleski, post #21026610]

Why it matters: One exploding component can blind or burn you faster than you can reach the switch.

Quick Facts

• Glass cartridge fuse breaking-capacity: 35 A – 1 500 A @ 250 V [Littelfuse 372 datasheet]. • Sand-filled HBC fuse interrupt rating: up to 10 000 A @ 125 V [Elektroda, Grzegorz_madera, post #21026715] • DC arcs last 3–5× longer than AC at equal voltage [IEEE Trans. PS, 2021]. • EN 166 safety goggles cost €3–€15 (Amazon EU, 2024). • 10 % of electrical accidents involve eye foreign bodies [OSHA Fact Sheet, 2022].

Why do glass fuses sometimes explode instead of just melting?

When the element vaporises, metal condenses on the glass, creating a conductive film. The arc then heats the tube unevenly until internal pressure bursts it [Elektroda, Grzegorz_madera, post #21026812] Sand-filled versions absorb the vapor and quench the arc before pressure builds.

What exactly is a fuse’s breaking capacity?

Breaking capacity is the maximum fault current the fuse can interrupt safely without rupturing its body. Littelfuse miniature fuses advertise 35 A–1 500 A at 250 V, or 10 000 A at 125 V for special versions [Elektroda, Grzegorz_madera, post #21026715] Choose a fuse whose interrupt rating exceeds the prospective short-circuit current.

How does sand filling prevent shattering?

Quartz sand surrounds the fusible link, absorbing heat and splitting the arc into many tiny, rapidly cooled segments. This shortens arc duration and keeps internal pressure low, so the body stays intact [Elektroda, 398216 Usunięty, post #21026920]

Are DC circuits riskier for fuses than AC circuits?

Yes. DC lacks natural current zero crossings, so arcs persist 3–5 times longer, demanding higher-rated or specialized DC fuses [IEEE Trans. PS, 2021]. Videos show even 3 A fuses sustaining arcs when powered from charged capacitors [Elektroda, ArturAVS, post #21027468]

When should I use an ultrafast (aR) fuse?

Use aR fuses to protect semiconductor devices such as IGBTs and MOSFETs. They clear faults within microseconds, before the device’s short-circuit withstand time expires. Standard ‘F’ or ‘T’ fuses react too slowly [IEC 60269-4].

Why do telecom systems ground the positive pole at –48 V?

Corrosion decreases when the chassis sits at the positive potential; electrons leave the metal, limiting anodic attack. Positive ground also reduces interference because cable shields reference the quieter side of the supply [Elektroda, web69, post #21056397]

What personal protective equipment is essential when powering high-energy circuits?

Minimum PPE: EN 166 goggles, insulating gloves, long-sleeved cotton, and closed footwear. Add hearing protection above 100 A prospective fault levels [OSHA 1910.335, 2022]. Many forum writers credit goggles with stopping molten metal droplets [Elektroda, kortyleski, post #21026610]

How can I power up a suspect device safely?

  1. Connect the DUT through an isolation transformer and series filament bulb or variac for current limiting.
  2. Wear goggles and keep one hand in pocket.
  3. Monitor voltage and current; shut down if the bulb flashes bright or the current spikes. This three-step method confines energy, giving the fuse and you time to react [Elektroda, prosiak_wej, post #21027306]

Can low-voltage busbars vaporise metal objects?

Yes. A 48 V, 2 × 2 500 A battery bank delivered >500 A through a painter’s metal bucket, vaporising it and deafening bystanders [Elektroda, web69, post #21054522] Large DC sources store enormous I²t energy despite modest voltage.

How should I dispose of blown fuses?

Treat them as electronic waste. Place glass shards in a sealed container, label as “sharp glass”. Recycle metals where facilities exist. Never reuse cracked holders; insulation can be compromised [EU WEEE Directive, 2012].
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