An electrical fault is an undesired event which occurs when a low impedance path is formed. Since electric current is inversely proportional to the impedance, a low impedance path causes very high current to flow through it. The faults in electrical power systems are classified into four types:
| Type of Fault | Current magnitude | Chance of Happening |
| Three-phase fault | Largest | Least common |
| Double line to ground | Large | Rare |
| Line to Line | Medium | Common |
| Line to ground | Smallest | Most common |
