Short circuit, overloading or device failure are the prime reasons for excessive current.
Putting wrong fuse in device can result in personal injury, fire and increase damage of your broken device.
Never replace a fuse with a higher amperage rating becouse your device can draw more current than its supposed to and whole thing can blow in your face.
Also dont put fuse in parallel or serial
Sometimes you can put smaller current rating fuse if e.g. your device is rated to draw 300 mA but fuse is 500 mA then you can put fuse that is close to 300 mA but not under 300 mA
Fuses are identified with the Amperage (A),Voltage (V) ,Burning speed (Fast-blow,Slow-blow,Time Delay) ,Size and Material (Ceramic,Glass,Plastic,Fiberglass)
There are Axial or Pigtail fuses with wire on the end and they are made for soldering on pcb
Slow blow can handle more current then they are marked for small amount of time and they are marked T and amperage (T2A, T1A, T0,25A) and Fast blow are blowing at marked current , they are marked F (F2A, F1A)
Voltage ratings are not marked in AC or DC
Ceramic fuses are more stable, some ceramic are also sand-filled for extra protection and they can handle higher current rating (more than 15A) a
Glass are see through and they blow faster becouse they dont have sand that will absorb heat
Examples: Most multimeters use 10A 250V and 250 mA - 500 mA 250V Fast blow fuse 5x20 mm
Step 1: Disconnect Device
It's not so hard you just need to disconnect plug that goes to main socket
I would also recommend to power off device first
NEVER OPEN DEVICE THAT IS STILL CONNECTED TO MAIN!
Step 2: Locating Fuse
When you pulling fuse out pull it gently so you wont damage fuse or some components
Step 3: Testing Fuse
For ceramic types you will need continuity checker/multimeter/ohmmeter
For continuity checker
Put fuse on black and red lead and if you hear beep than your fuse is ok, if theres no beep fuse is burned
Set multimeter to ohm setting (closest to 1Ω) and put one lead on each end of the fuse and look at the display
If the meter shows a less than 1Ω then the fuse should be okay, if it show that theres no connection (on my multimeter is 1 on left side) then fuse is burned
Step 4: Buying New Fuse
There should be written something like : T2A250V, F1A250V that's fuse rating
T is for slow blow fuse and F for fast blow fuse
2A or 1A is Amperage rating its usually just number and A
250V is Voltage rating its number and V
And then just measure the size of fuse
In small electrical device is usually 5x20mm
There are 5x20mm, 5x15mm, 6.3x32mm, 3.6x10mm, 5x25mm and 10x38mm