I want to add a fuse to my project to protect against a short. I am using glass fuses and this is my first time using fuses so I decided to experiment with them. I am putting 1w resisters in parallel so I can see what the fuse does at different amperages, and measuring amperage of the circuit with my multimeter. Here is what I'm seeing.
For my 0.2A 250v rated fuse running at 5v DC
200mA: No change to the fuse
400mA: No change to the fuse (I would have expected the fuse to burn up at this point)
600mA: No change to the fuse
800mA: The fuse starts glowing, but does not burn up
After this point adding more resistors increases the amperage only a small amount. However the fuse still did not burn.
I then just shorted my power supply directly through the fuse (My power supply will output up to 3A which is 15x the fuse's rating), and the fuse still did not burn up. The amperage raised to 1A and just stayed there, I left it for about 10 minutes, and the fuse stayed glowing, the glass became discolored, but still allowed 1A to flow. The fuse seems to be acting more as a resistor than a fuse. It also began to heat up, this is not really what I was hoping for.
I've tried this with several fuses, and half of them share this behavior with peeking at 1A and staying there. The other half just burn up quickly as I would expect.
The project that I want to add a fuse to is going to should draw a maximum 300mA, I was going to put in a a 0.5A fuse, but after my experiments, I think that a 0.2A fuse would be safer, even though it is rated at less then the maximum current the project will draw. Is this a reasonable plan?