What is a Fault Current?

Malcolm Tatum

Also known as a short-circuit current, a fault current is a term used to describe a situation in which the flow of current that is traveling through an electric circuit is not within a normal range. This type of abnormal or unusual flow of current can be caused by a number of different issues, including a short-circuit of electrical equipment or some defect that is adversely affecting the path of the current, causing the output to be somewhat low. When the flow of current falls outside a normal range, equipment that is designed to prevent short circuits will not respond correctly, making it necessary to correct the situation as quickly as possible.

Locating a fault current depends on the overall construction of the wiring system involved.
Locating a fault current depends on the overall construction of the wiring system involved.

The process of locating a fault current will vary slightly, depending on the overall construction of the wiring system involved. With a simple system, it is sometimes possible to identify the origin of the problem by making a simple inspection of the wires that make up the system. In more complex systems where the wiring is encased and may run for extremely long distances, there is usually the need to utilize equipment that actually traces and measures the flow of current from the point of origin to the point of termination. One example of this type of equipment is the time domain reflector, which emits a pulse that runs the length of the wiring and registers the pulse as it returns. The data derived from the pulsations makes it possible to get a good idea of exactly where the impediment or defect is located, expediting the repair of the wiring and eliminating the fault current.

Correcting a fault current is very important not only to the ongoing operation of the electrical system, but also to the safety of those who live and work around that system. Abnormal flows of current can lead to power surges that damage equipment that is powered by the current supplied by the wiring, or possibly charge the devices so that when they are touched, an electric shock is administered. Depending on the nature of the fault current and the amount of voltage involved, that shock can be sufficient to cause death.

There are different standards used around the world to define what constitutes an irregular or fault current. Various countries set regulations that require the installation of circuit breakers and other safeguards that help to minimize the potential dangers associated with short-circuits. It is not unusual for standards to be developed that apply to residential as well as commercial settings, making it necessary to implement safety measures that are relevant to the amount of current that is normally delivered in each instance.

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Discussion Comments


Why we need GFCI (Ground Fault Circuit Interrupter) outlets in our kitchen and bathrooms is relatively simple: We need them to keep us from getting shocked.

A normal panel circuit breaker is to protect you from a fire. When a positive and a neutral wire touch each other it creates a short circuit that a large unregulated amount of electricity can go though, which will quickly overload the capability of the wire, making it get hot like a stove element and possibly setting fire to your home. A panel breaker will trip when the voltage going though the wire exceeds the specification of the circuit. This is most often 15 amps.

A GFCI monitors the amperage in both the positive and neutral wire and trips when there is a difference between the two. It does this because when there is a difference in voltage the unaccounted voltage could be coming from an appliance like a hair dryer that has gotten wet and is feeding voltage into the water. You may in turn touch the water and get shocked.

How all those different technologies work internally, I do not know. Of course a fuse works by running the circuit though a filament that will burn up if too much voltage passes though it, but panel breakers and GFCIs are a mystery to me!


How do Ground Fault Circuit Interrupters work verses panel breakers or fuses? Why do we need extra circuit interruption on a circuit when we already have a breaker on that panel?

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