Overcurrent is any current load in excess of the safety rating of equipment or the ampacity of a conductor. Overcurrent may result from an overload, a short circuit, or a ground fault. Overcurrent does not always cause a fire. The magnitude and direction of the overcurrent must be sufficient to heat the wire to a temperature that ignites surrounding combustibles. Sustained overcurrents that can cause damage or fire (called overload) should trip the fuse or breaker, opening the circuit and stopping the flow and heating. However, items such as an extension cord can reduce the conductor size between the load and the circuit protection and can overheat the wire without tripping the protection.
For more information on this term, see the interFIRE VR Resource File article: Examples of Common Accidental Causes: Overloaded Circuit