What Causes Overcurrent in an AC Motor?

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Overcurrent is a common problem in AC motors and other electronics.

Overcurrent is a condition in electronics when too much current is running through an electrical circuit. This problem is relatively common in the electrical engineering field. Overcurrent protection is one of the essential elements of a proper electrical installation. The problem has many symptoms and can eventually lead to permanent damage to the motor or electrical device. A few of the symptoms of overcurrent in a motor are shorts, blown fuses and unintended switching on and off of the motor.


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A fault is a general term that describes any sort of malfunction of the electrical wiring within the motor. Faults can arise from damage or incorrect installation of a unit. In most faults, the electrical charge is carried over a route that is not intended to carry a current. This can be any extraneous piece of metal or any part of the machine that can carry a current. This causes the flow of current to rise dramatically, creating overcurrent.


Miswiring can cause overcurrent in motors. If the wiring is incorrect on a motor, it can lead to shorts and other problems. Shorts can cause fires and if left unattended, will ruin the motor. This can be avoided by checking the schematics of engines to ensure that the wiring is correct and examining each wire individually to make sure there is no fraying.


Phase-to-Phase Insulation

If the phase-to-phase insulation breaks down, this can cause overcurrent. This insulation is intended to prevent the current from finding a circuit in an unintended place. It is essentially wrapped around a wire to prevent its conducting to another object or piece of the motor. Phase-to-phase insulation is not supposed to respond to electrical charges, so if the insulation begins to peel from a wire or a piece of metal, the electrical charge can be conducted through an area it is not meant to go through. This can lead to grounding faults.


The IGBT is also known as an "insulated gate bipolar transistor" and is a semiconductor power unit that has three terminals. The IGBT controls the switching on and off of electrical devices. In most electrical devices, one transistor in the IGBT pushes current out to force it into positive voltage. A second transistor pulls down. "Shoot through" is the result of both of these devices running at once.


Malfunctioning Circuit Breakers or Fuses

Most electrical devices with complex wiring come with circuit breakers and fuses. These are intended to protect the devices from overcurrent. Circuit breakers and fuses essentially act as gatekeepers, allowing the correct amount of voltage to pass over the current. Circuit breakers generally must be bought to match the motor or device you are looking to regulate but fuses are almost universal, so that any fuses can be placed in any device. If either of these preventative devices breaks down, overcurrent can become a problem.



Brett Thorne

Brett Thorne began writing in 2007. He has been on staff with "The University Star" as an editor and writer and is regularly published on the Austin music blog Red River Noise. He is pursuing a bachelor's degree in general studies with an emphasis in journalism, sociology and business administration from Texas State University.