SMIN 10 pcs F2AL 250V Glass Fast-Blow Fuse 6x30 mm (2Amp)

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This, with suitably chosen alloys, nicely gives the characteristic needed for a surge resistant fuse.

In slow blow fuse the wire is (generally) coiled to provide proximity to heat energy from the adjacent wire plus the cooling path is increased by having a much longer wire length and thus thermal path to the mounting points.

There are many variations on this design and it gives manufacturers a lot of parameters for adjusting the fuse characteristics. I recently gave a talk to my local amateur radio club on the subject, and what follows is from the script I wrote for that talk. In this case, at the lower temperature of the wire, the solder diffused into and alloyed with the silver to create a region of high resistance in the spot, which would glow red hot, with the wire rupturing next to it. Incidentally, A good design should have F or T plus the fuse rating marked on the PCB where the fuse holder is. It so hard looking for a fuse that has the EXACT inscription 2A 250Vall I can find is 2AL 250 Vis this the same type?

I was an electrical engineer in the 1950s, part of my work was concerned with testing and selecting fuses. If the fuse is in the mains input lead before any power supply unit, then it needs to sustain the start-up current required to charge the main filter capacitors - so, slow blow. The fuse within a plug is a safety device that is designed to protect the lead rather than the appliance therefore it will blow if the circuit overloads or there is a fault. Put a T in there, and things can suffer a bit of damage if there IS a problem, because the fuse leaves power applied for rather longer.Occasionally, as in the image above, a by-pass wire across the spring is used to adjust the characteristics of the fuse. To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average.