What Is an Overcurrent? Definition, Causes, Protection

What is meant by overcurrent?

Overcurrent: electric current exceeding the rated electric current [SOURCE: IEC 60050-826].

NOTE. For conductors, the rated current is considered as equal to the current-carrying capacity.

An overcurrent is any electrical current which exceeds the rated current of any part of the building installation or the rated current of the electrical equipment used in it, for example: the rated current of a circuit, the continuous current-carrying capacity of a conductor, the rated current of a circuit breaker, a fuse, a residual current device, etc.

An overcurrent in any part of the electrical installation of a building can lead to overheating, combustion and, consequently, fire in the building. For this reason, overcurrent protection is provided in electrical installations of buildings.

During transients, short-term overcurrents occur in the electrical circuits of the building installation. For example, switching on an current-using equipment is usually accompanied by inrush currents that are several times higher than its rated current. If the rated current of the current-using equipment is comparable to the continuous current of the conductors to which it is connected, the inrush current and the time of its flow must be taken into account when selecting their cross-section. The characteristics of overcurrent protection devices should also be chosen taking into account the possible inrush currents.

Overcurrents may or may not have harmful effects depending on their magnitude and duration. Overcurrents can be caused by overloads in current-using equipment or by faults such as short circuits or earth faults.

Overcurrent protection

Requirements for overcurrent protection are specified in IEC 60364-4-43.

Persons and animals must be protected from injury and property damage caused by high temperatures or electromechanical stresses caused by any overcurrents that may flow through conductors. This protection can be provided by limiting the overcurrent to a safe value or by reducing the duration of its exposure.

Note: In TN systems, ground-fault currents can be comparable to short-circuit currents.

Types of overcurrents

Normative documentation distinguishes between two basic types of overcurrent – overload current and short-circuit current. The occurrence of overcurrent is usually not associated with the occurrence of any fault. Short-circuit current usually occurs when a single fault or multiple faults occur, i.e. in the emergency mode of the electrical installation of a building. An overcurrent can also be a earth fault current if the fault occurs in a electrical installation of a building which conforms to the TN-S, TN-C or TN-C-S system earthing type. In TN systems, the earth-fault current can be equal to the single-phase short-circuit current.

Overcurrent in NFPA 70

Overcurrent: Any current in excess of the rated current of equipment or the ampacity of a conductor. It may result from overload, short circuit, or ground fault [Definition from NFPA 70].

Informational Note: A current in excess of rating may be accommodated by certain equipment and conductors for a given set of conditions. Therefore, the rules for overcurrent protection are specific for particular situations.


What Causes an Overcurrent?

An overcurrent is caused by a too high current passing through an electrical circuit. This can be due to a number of reasons, such as a short circuit, faulty wiring, or overloaded circuits. Overcurrents can be dangerous and cause damage to electrical equipment, so it is important to be aware of the potential causes and take steps to prevent them.

What Are the 3 Types of Overcurrent?

There are three types of overcurrent: excessive current, overload current, and fault current. Excessive current is a condition where the current in a circuit exceeds the rated amperage of the circuit breaker or fuse. Overload current occurs when the current in a circuit exceeds the maximum amperage that the wires can safely carry. A fault current is an abnormally high level of current that results from a short circuit or ground fault.

What Is the Difference Between Overcurrent and Overload?

Overcurrent and overload are two important concepts in electrical safety. Overcurrent is a condition where the current in an electrical circuit exceeds the rated amperage of the circuit, while overload is a condition where the current in an electrical circuit exceeds the safe amperage for the conductor or device.

While both conditions can lead to damage or failure of electrical equipment, overcurrent is typically more dangerous because it can cause fires. Overload, on the other hand, usually results in damaged equipment but not fires.

It’s important to understand the difference between overcurrent and overload so that you can take steps to prevent them. To help prevent overcurrent, use circuit breakers or fuses that are rated for the maximum amperage of the circuit. To help prevent overload, make sure that the conductor or device can safely handle the maximum amperage of the circuit.

How do You Deal with Overcurrent?

There are a few different ways to deal with overcurrent. The first is to use circuit breakers. Circuit breakers are devices that automatically shut off power to a circuit when it senses an overload of current. This protects the wiring from overheating and potentially causing a fire.

Another way to deal with overcurrent is to use fuses. Fuses are devices that contain a metal strip that melts when too much current flows through it. This interrupts the flow of current and protects the circuit from damage.

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