The biggest cause of starter motor failure is electrical overloading/excessive current draw, often from:
Frequent starts (inrush current overheating components).
Motor/load issues (seized bearings, jams increasing resistance).
Other key causes:
Worn contactors (arcing damage).
Poor maintenance (dust, corrosion).
Improper sizing/installation.
Environmental stress (heat, moisture).
Preventive steps:
Match starter to motor specs.
Regularly clean, inspect contacts/relays.
Address mechanical issues promptly.
Use rated enclosures for the environment.