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Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ.

RE: "not all fuses react to inrush current the same way"

And that was the intent of my original post, to try and get a better understanding of "why".

I once posted an observation on the Asylum about the element of a 0.25A fast-blo glass fuse glowing bright orange when I first apply 24 VDC to one of my phono stages, which has a quiescent current draw of about 30mA. It does it every time I've switched the power on. The glow lasts for about a second and then looks normal, and yet the fuse has never opened (i.e. "blown").

According to Neolith in his reply to my post, ceramic fuses contain silica. Pure speculation on my part, but I wonder if that silica doesn't allow the resulting heat of a "glowing orange" fuse element to dissipate as quickly as an element in the open air of a glass fuse would, causing the fuse to blow. Still, you'd think that if that were the case, manufacturers like Buss, etc. would take that into account when assigning their fuses over-current protection ratings.

My Nelson Pass First Watt F1J (not a DIY amp) has thermistors in the power supply, and I've never had its fuse open, so your point regarding inrush current is well taken. The schematic calls for a "4A slow", and I got curious while typing this to see if the fuse was glass or ceramic. It turns out it's a 2.5A slow blow glass fuse, 1.5A under spec, and yet has never blown. I guess those thermistors do their job!


"Suddenly, I'm not half the man I used to be. 'Cause now I'm an amputee" J. Lennon


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  • RE: "not all fuses react to inrush current the same way" - 1973shovel 07:03:47 05/08/17 (0)

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