Overcurrent protection devices (OCPDs) are pieces of equipment used in electrical systems that are at risk of overcurrent owing to overloads, short circuits, or ground faults. Fuses, circuit breakers, and overcurrent relays are the most prevalent types of protection devices. They serve to protect persons or property from damage caused by an overloaded or malfunctioning system.
The purpose of an OCPD is to prevent excessive current from flowing through a conductor of the system, which could cause a fire or otherwise damage equipment or endanger the lives of those working around the equipment.
An OCPD consists of a casing with two or more sets of contacts inside: one set to open the circuit if too much current flows through it; another set to close the circuit again once the overload has been removed. A third set of contacts may be included to also interrupt power to various parts of the system if necessary. Some OCPDs have motors that can automatically open them when excess current is detected. These are called motor-operated circuit breakers and are useful for protecting people from living in dangerous areas where they might be overcome by smoke while trying to escape a burning building or apartment.
Other types of OCPDs are operated manually by an electrician who visits each site where these devices are installed. This type of inspection is necessary because not all buildings are equipped with automatic shutoff valves that would close the circuit if anything went wrong.
Circuit breakers and fuses safeguard circuit wiring from overcurrent damage. Overcurrent protection devices, or OCPDs, come in two varieties: circuit breakers and fuses. Every electrical circuit in a home must have its own OCPD that is rated appropriately for the circuit wiring. A circuit breaker replaces several smaller fuses to protect against excessive current flow through a section of wire.
Because electricity is transmitted to homes and businesses through thick wires running from place to place, it can be difficult to determine exactly where a problem portion of a circuit might be. If you are working on a circuit that contains fixtures such as lights, heaters, air conditioners, and appliances that have motors, then you should use caution not to overload them. Fixtures will usually specify how much current they can handle, so it's best to follow their instructions when repairing circuits.
The term "overcurrent" means too much current flowing through a conductor, which can cause damage fast enough to be visible. The two main categories of overcurrent conditions are "short circuit" and "open circuit". In a short circuit, all the wires connected to one circuit destination fuse or switch melt or burn up before any other part of the system is damaged. In an open circuit, no current is flowing through the wire connection between your power source and the item needing repair, so there's no risk of overheating it.
Circuit breakers and fuses are examples of overcurrent protection devices. Overcurrent protection devices are designed to safeguard against the potentially hazardous effects of overcurrents, such as an overload current or a short-circuit current, which generates a fault current. An overload may be caused by a large number of factors such as a too-large load, a power line outage, or a malfunctioning unit. The overcurrent protection should not only detect but also limit the current in order to prevent any damage to the equipment being protected.
The two main types of overcurrent protection devices are fuse boxes and circuit breaker panels. A fuse is a simple on/off device that opens when it fails in order to protect other components from failing due to high heat generated by the current flowing through it. Fuse boxes contain numerous small glass or ceramic fuses. Each fuse has an aluminum rod with oxide powder inside and outside the tube. If there is no voltage applied to the fuse, the powder will not combust and the fuse will not blow. When electricity goes into the fuse, the powder inside the tube will burn, releasing gas which forces the rods apart and creates a spark which blows the fuse open.
Circuit breaker panels use switches instead of fuses for overcurrent protection. They are more reliable than fuses because they cannot fail open like they can if they have blown out. Circuit breaker panels can also handle much higher currents than fuse boxes can.
An overcurrent protection device safeguards the circuit by opening when the current reaches a value that causes an excessive or dangerous temperature rise in conductors. The majority of overcurrent protection devices respond to both short-circuit or ground-fault current levels and overload circumstances. Temperature-sensitive devices open at lower currents than do other types of overcurrent protectors.
The two main categories of overcurrent protection devices are magnetic and thermal. Magnetic overcurrent protection devices use the behavior of magnets to detect abnormal voltage conditions on a conductor. When electricity is fed into a magnetic overcurrent protector, its core of magnetically susceptible material becomes polarized so that it can hold a permanent magnet. If there is a loss of power to the coil that surrounds this core, then the magnet will not attract itself through the core, thus indicating a short circuit or ground fault and requiring action to be taken to prevent damage to other equipment on the line or human injury from contact with energized parts.
Thermal overcurrent protection devices use the heat generated by resistance wires within their casing to determine if enough current is passing through them to require action to be taken. If so, the devices will open to interrupt the circuit.
Overcurrent protection devices may be incorporated into housings that connect one or more conductors to a load terminal, or they may be attached directly to the conductor sheathing.
Overcurrent protection safeguards against excessive currents or currents that exceed the equipment's allowable current rating. Overload protection safeguards against a running overcurrent that might cause the protected equipment to overheat. As a result, an overload is a sort of overcurrent. However, an overload is usually defined as the state of something that is greatly exceeded; in other words, an overload is a very high level of current flow.
In electrical systems, overcurrent protection is provided by circuit breakers and fuses. A breaker will open the circuit if too much current flows through it. The amount of current that causes a breaker to open is called the breaker's "trip point." A fuse will burn out if not removed from its housing soon after it has blown.
In transmission systems, overcurrent protection is provided by automatic voltage regulators (AVRs). An AVR reduces the voltage of an incoming power line so that less than the maximum allowed for a given system configuration occurs on the conductors feeding power into the transmission substation. This prevents overloading of the transmission lines, which would otherwise lead to their damage. If an AVR detects that the current flowing through it is higher than its setting, it will reduce its output voltage accordingly. This reduction in voltage makes sure that no more current can flow through the device. Transmission lines are designed to carry certain amounts of current at certain points in time, typically expressed in amperes.