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Overcurrent Protection Device (OCPD)

Last updated: September 3, 2019

What Does Overcurrent Protection Device (OCPD) Mean?

An overcurrent protection device (OCPD) is a piece of equipment used in electrical systems that are at risk of experiencing overcurrent due to overloads, short circuits, or ground faults. An overcurrent is any situation in which the amount of current (amperes) in a system (e.g., an electrical circuit) exceeds the amount of current that the system is designed to safely handle. In overcurrent situations, an OCPD will re-route or disable current flow through the system to make it safe.

The most common of these protection devices are fuses, circuit breakers, and overcurrent relays. In cases where an overcurrent occurs, these devices will break the circuit through which the current is flowing, eliminating or re-routing the current flow. OCPDs only work in relation to the amount of current flowing through them and will therefore not respond to an overcurrent isolated to another part of the circuit. An example would be a circuit that is improperly routed through an extension cord with a lower voltage tolerance than the rest of the circuit.

Safeopedia Explains Overcurrent Protection Device (OCPD)

The use of overcurrent protection devices is a standard part of electrical safety, and it is prescribed in the United States as part of the National Electrical Code (also known as NFPA 70). Individuals working in proximity to devices at risk of overcurrent face dangers from electrical shock and fire, both of which can be caused by the damage to electrical equipment due to an overcurrent. OCPDs can also prevent explosive ignition and arc flashes related to voltage overload and other electrical malfunctions.

Most OCPDs (e.g., fuses) are found in the primary service panels (i.e., the “fuse box”), as well as associated electrical feeders and branch circuits, which are typically connected to their own breaker systems. Industrial electrical equipment also uses overcurrent relays within equipment to directly protect against overcurrent damage.

The particular OCPDs necessary to protect against overcurrent vary depending on the hazards associated with a given electrical system. For example, in systems in which ground and arc faults are present as potential hazards, the use of ground fault circuit interrupters (GFCI) and arc fault circuit interrupters (AFCI) is necessary to mitigate the risk of an overcurrent-related shock or fire. Overload protection devices are a type of OCPD that are designed to protect against sustained overcurrent, and they include the use of relays and “slow blow” fuses.

The correct use of OCPDs (and their distribution in specific branch contexts) is necessary for safe OCPD use. If an OCPD is exposed to a level of voltage it is not designed to deal with, it may itself rupture or explode. Proper grounding of service boxes and equipment can mitigate this risk.


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