A fuse will normally fail for one of three reasons: excessive current in the circuit, fatigue or poor contact. By inspecting the failed fuse we can often determine the cause of the failure.
• Excessive current can be caused by a short circuit or by an excessive load being imposed on a motor. Examples:
- Wiper blade frozen to the windshield
- Window too tight in the runner
A fuse that has failed due to excessive current will have a 2 to 3mm section melted away at the center. The circuit and components should be checked and any repairs needed should be done prior to replacing the fuse.
• Fuse fatigue is caused by the fluctuations in current when the power is switched ON and OFF. The ON/OFF current will heat and cool the fuse and eventually the fuse will burn out. A fuse that has failed due to fatigue will look like the center of the fuse was cut with a thin knife.
• Poor contact between the fuse and the fuse holder causes resistance which generates heat. If the fuse gets too hot it burns and fails. On bladed fuses the plastic may melt and the element will melt much like with excessive current. On tube fuses, the contacts at the cap to element will melt. Prior to replacing the fuse, the holder should be cleaned and repaired to provide better contact with the fuse.
• Excessive current can be caused by a short circuit or by an excessive load being imposed on a motor. Examples:
- Wiper blade frozen to the windshield
- Window too tight in the runner
A fuse that has failed due to excessive current will have a 2 to 3mm section melted away at the center. The circuit and components should be checked and any repairs needed should be done prior to replacing the fuse.
• Fuse fatigue is caused by the fluctuations in current when the power is switched ON and OFF. The ON/OFF current will heat and cool the fuse and eventually the fuse will burn out. A fuse that has failed due to fatigue will look like the center of the fuse was cut with a thin knife.
• Poor contact between the fuse and the fuse holder causes resistance which generates heat. If the fuse gets too hot it burns and fails. On bladed fuses the plastic may melt and the element will melt much like with excessive current. On tube fuses, the contacts at the cap to element will melt. Prior to replacing the fuse, the holder should be cleaned and repaired to provide better contact with the fuse.
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