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I am sure you have seen automotive 'Blade' fuses. They are special fuses constructed to protect equipment that is DC powered. I have asked around and determined that a 125v DC rated fuse is more than acceptable to protect 240vac equipment without arcing due to the zero-voltage presence in AC power.

Blade Fuse

Blade Fuse

Credit: JSumo

Blade Fuse Filament

Blade Fuse with "Horseshoe" Element Visible

Credit: Ferrules

I am in need of a fuse handling similar current but in a package that is slightly smaller. I will not go into details, but all other fuse package types will not suit my application, only the blade fuse or something extremely similar. My plan is to remove the casing, cut the leads down, and re-place the filament in my own packaging, made of the same material. Blade fuses also give the advantage of not requiring an inert gas inside, making them an even more attractive choice for this application. Eventually, I will approach a blade fuse manufacturer and have them make my custom fuse. Same element, same material, different outer package, but too high cost for a prototype ;).

My question today concerns not AC or DC, but the physical nature of these fuses' construction. There is virtually no information on the internet about the stresses on the element within the fuse. Is the plastic case there just for safety reasons or does it also exert a positive or negative compression force on the element, to encourage it to fuse right in the middle?

For those who do not have experience with the manufacturing of these fuses, perhaps you could share in the comments some advice on how to measure if the element is in compression without bending it in the process?

Edit:

There seems to be some confusion as to what I am trying to design here. I am making a smart fuse (regular fuse + extras). I will leave you to guess what those 'Extras' are for NDA purposes. The 'regular fuse' that will server as the core of this design requires bulk order from china and they offer no English support. This post simply served as a general 'are blade fuses more than just a piece of (precisely machined) metal with a plastic cover' inquiry. This will save me from placing a custom order for some of the most expensive blade fuses out there just for an experiment that will be more involved than I originally bargained for. Blade fuses are not my only option, but if the metal part inside the case is not in tension to blow right in the middle, than they are the best option out there because they:

  1. Blows in a predictable physical location (vs Cartridge type that can blow anywhere along the filament)

  2. Are not surrounded by an inert gas, making prototyping custom fuses easier

  3. Are lightweight

  4. Have an easily removable filament

  5. Have the potential to be cut down to a smaller size so that their longest dimension is smaller than any other fuse out there for their current rating.

After the bit of feedback I have gotten, I think I will grab a cheap bag of these off ebay or stop by my local garage and get testing. I will post any interesting developments.

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  • \$\begingroup\$ Fuses are concerned with "I2t energy" -> lead to Delta Temperature rise ... some usefull datas ... littelfuse.com/~/media/electronics/product_catalogs/… page 7 \$\endgroup\$
    – Antonio51
    Jul 4 at 19:19
  • \$\begingroup\$ The element will blow at its thinnest point because the current causes the highest amount of heating there. The plastic enclosure offers insulation and a means to handle the whole assembly without damaging the element. \$\endgroup\$
    – Finbarr
    Jul 4 at 19:19
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    \$\begingroup\$ I doubt very much anyone can answer your question with authority. Therefore you will have to try your modifications, then test the resulting fuse to make sure it meets your requirement. A word of caution: you may have a hard time convincing UL or similar agencies that your product is safe, if it relies on the fuse operating properly. And, to put it candidly, I think you are nuts to follow this course of action. There HAS to be another way. \$\endgroup\$
    – mkeith
    Jul 4 at 19:21
  • \$\begingroup\$ There are a zillion different fuse options out there. Its not true you that there isnt a suitable one for your purpose. You just havent found it yet. Check places that stock those options like MOUSER or DIGIKEY \$\endgroup\$
    – Kyle B
    Jul 4 at 19:23
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    \$\begingroup\$ Smells like wheel re-invention. There are a billion different kinds of fuses out there, it's hard to imagine you can't find an OTS one that would work unless your operating environment is truly unprecedented \$\endgroup\$
    – ChateauDu
    Jul 4 at 19:54
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Fuses melt where they do because that is the precisely machined part to fail.

They are not put under tension or compression in that plastic package, at least not the ones I took apart.

The main reason they are in that plastic package is so that the general public can recognise the size by the colour as well as the numbers and they are easy to handle.

Go back in time and early car fuses were just loose wires that had to be fixed by screws or into clamps. Then came glass cartridge fuses which the general public would break often basically due to clumsiness.

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  • \$\begingroup\$ This is exactly what I assumed. I have been working with fuses of all kinds for over 10 years, and I imagined there was no compression or tension, but I read a strange post by someone who claimed to be a fuse manufacturer and that their fuses relied on a physical tension on the element so that it melts exactly in the middle. I have never seen a single datasheet that mentions compression on the element for blade fuses, however, which is why I asked. [Obsolete part of comment removed by a moderator.] \$\endgroup\$
    – Hackstaar
    Jul 4 at 22:42

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