The motor protection relay provides protection from overcurrent. Overcurrent protection is protection against excessive currents or current beyond the acceptable current rating of equipment. It generally operates instantly. Short circuit is a type of overcurrent. Magnetic circuit breakers, fuses and overcurrent relays are commonly used to provide overcurrent protection.
An overcurrent exists when current exceeds the rating of conductors or equipment. It can result from overload, short circuit, or ground fault.
An overload is a condition in which equipment or conductors carry current exceeding their rated ampacity. An example is plugging two 12.5A (1,500W) hair dryers into a 20A branch circuit.
A short circuit is the unintentional electrical connection between any two normally current-carrying conductors of a circuit (line-to-line or line-to-neutral).
A ground fault is an unintentional, electrically conducting connection between an ungrounded conductor of a circuit and the equipment grounding conductor, metallic enclosures, metallic raceways, metallic equipment, or earth. During a ground fault, dangerous voltages and abnormally large currents exist.