The three major categories or types of overcurrent are overload, short-circuit, and ground-fault.

1. Overload: Overload occurs when the current flowing through a circuit exceeds the designed or rated capacity of the conductors or equipment. This typically happens when the connected load draws more current than the circuit or device is intended to handle. Overloads can lead to overheating of conductors and equipment, insulation breakdown, and potential fire hazards.

2. Short Circuit: A short circuit occurs when a low-resistance path is established between conductors, bypassing the intended load. This results in a sudden surge of current flow, often limited only by the impedance of the circuit. Short circuits can cause extensive damage to equipment, overheating, arcing, and even fire. They're typically characterized by a rapid increase in current flow and often result in circuit breakers or fuses tripping to interrupt the current.

3. Ground Fault: A ground fault occurs when an unintended connection is made between a live conductor and the ground or earth. This can happen due to insulation breakdown, equipment failure, or improper wiring. Ground faults can result in excessive current flowing through the ground path, leading to equipment damage, electric shock hazards, and tripping of ground fault protection devices like ground fault circuit interrupters (GFCIs).

These three types of overcurrent are critical considerations in electrical system design, installation, and maintenance to ensure the safety and reliability of electrical circuits and equipment. Various protective devices, such as circuit breakers, fuses, and ground fault protection devices, are used to detect and mitigate the effects of overcurrent conditions.