A short circuit is an abnormal connection between two nodes of an electrical circuit designed to be at different voltages. This results in an electric current limited only by the Thevenin equivalent resistance of the rest of the grid, which can cause circuit damage, overheating, fire or explosion. Although, as a rule, the result of a fault, there are cases where short circuits are intentionally caused, for example, to protect the percussion circuits for voltage sensors.
In circuit analysis, a short circuit is defined as a connection between two nodes that forces them to be at the same voltage. In an “ideal” short circuit, it means there is no resistance and therefore there is no voltage drop in connection. In real circuits, the result is a connection with almost no resistance. In such a case, the current is limited only by the resistance of the rest of the circuit.
For Example: A common type of short circuit occurs when the positive and negative terminals of a battery are connected to a low resistance conductor, such as a cable. With low connection force, a high current will flow, which will cause a large amount of energy to be delivered in a short period of time.
A high current flowing through a battery can cause a rapid rise in temperature, which could result in an explosion with the release of hydrogen gas and electrolytes (an acid or a base) that could burn the tissue and cause blindness or even death. Overloaded wires will overheat, causing damage to the wire insulation or causing a fire. High current conditions can also occur with electric motor loads in stationary conditions, such as when the rotor of an electrically driven pump is blocked by debris; This is not short, although it may have some similar effects.
In electrical devices, unintentional short circuits generally occur when the insulation of a cable breaks down or when another main material is introduced, allowing the load to flow along a path different from what is desired.
In network circuits, short circuits can occur between two phases, between phase and neutral or between phase and ground. It is probable that such short circuits generate a very high current and, therefore, rapidly activate an overcurrent protection device. However, short circuits can occur between neutral conductors and ground and between two conductors in the same phase.
These shorts can be dangerous, especially because they can not give rise to a high current and, therefore, are less likely to be detected. Possible effects include the unexpected activation of a circuit that is supposed to be isolated. To help reduce the negative effects of short circuits, power distribution transformers are deliberately designed to have a certain amount of leakage reactance. The leakage resistance (typically around 5 to 10% of the total load impedance) helps limit both the magnitude and the rate of increase of the fault current.
A short circuit can lead to the formation of an electric arc. The arc, a channel of hot ionized plasma, is very conductive and can persist even after significant amounts of original material have evaporated from the conductors. Surface erosion is a typical sign of damage to the electric arc. Even short springs can eliminate significant amounts of material from the electrodes.
The temperature of the resulting electric arc is very high (tens of thousands of degrees Fahrenheit), causing the metal on the contact surfaces to melt, fish and migrate with the current, and escape into the air in the form of fine powders.