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].
What does “PU equipment” mean in this context?
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?
- Connect the DUT through an isolation transformer and series filament bulb or variac for current limiting.
- Wear goggles and keep one hand in pocket.
- 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.
What’s an example of a catastrophic fuse failure?
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].
Generated by the language model.
Comments
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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... [Read more]
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. [Read more]
Equipment P common U use -. means domestic... ;) (I didn't make that up). [Read more]
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,... [Read more]
@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... [Read more]
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... [Read more]
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... [Read more]
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). [Read more]
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... [Read more]
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. [Read more]
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... [Read more]
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... [Read more]