Fundamentals of Short Circuit

The development of the electronics industry has had a profound impact on modern society, encompassing nearly all aspects of production, work, and daily life. Due to its wide-ranging influence, circuit faults have become a common occurrence, with short circuits being one of the most prevalent and damaging faults. In this article, TechSparks will gradually introduce the definition, consequences, and protective measures of short circuits.

Definition of Short Circuit

In an electrical circuit, current follows a pre-designed path for transmission. However, similar to human behavior, current tends to seek the path of least resistance, often deviating from the intended circuit path to create a short circuit. This is the basic concept of a short circuit.

Short circuits are typically categorized into two types: power supply short circuits and appliance short circuits.

Power supply short circuits occur when current flows from the positive terminal of the power supply and returns to the negative terminal without passing through any appliances. According to Ohm’s Law: I=V/R, the voltage of the power supply remains constant while the wire resistance is very low, resulting in a significantly increased circuit current, ultimately leading to power supply failure.

power supply short circuit

Appliance short circuits, on the other hand, occur when unexpected wiring in the circuit causes the current intended for the appliance to bypass it. In such cases, the appliance is shorted, leading to potential damage. Appliance short circuits may also occur due to internal wiring contact within the appliance.

electrical appliance short circuit

Why Short Circuits Are Dangerous

The hazards caused by short circuits are significant, as demonstrated by Ohm’s Law. With a fixed power supply voltage, a short circuit results in a dramatic increase in current flow due to the reduced wire resistance.

For example, consider a circuit with a voltage of 240 volts and a resistance of 24 ohms. Under normal circumstances, the current would be 10 amps. However, in the event of a short circuit, if the resistance drops to 2.4 ohms, the current would rapidly increase to 100 amps.

During circuit design, engineers typically design components to handle normal operating conditions. However, when faced with a sudden increase in current, wires or components may be overloaded and destroyed, potentially leading to fires or other disasters.

In digital circuits, abnormal current caused by a short circuit can alter the operating conditions of other parts of the circuit, including input/output ports or logic gates. This can result in the receiver being unable to decode signals correctly, leading to data loss.

Additionally, accidental contact with exposed conductors by the human body can result in electric shock or even electrocution, as the human body’s resistance is much lower than that of a conductor.

First Aid Measures:

In the event of an electric shock accident, never directly touch the electrified person or conductor. Immediately disconnect the power source and use insulating materials (such as wooden sticks) to separate the person from the conductor to prevent secondary electric shock accidents.

First aid measures for electric shock accidents

Causes of Short Circuits

  • Wire Wear or Damage:

This is one of the most common causes of short circuits, often resulting from prolonged use or external factors (such as rodent damage). In such cases, direct contact may occur between wires, causing a short circuit.

  • Component Failure:

When components in the circuit fail due to aging, overload, or improper use, abnormal connections may occur inside, leading to short circuits. For example, the insulation of a capacitor may be damaged, resulting in a direct connection between the positive and negative terminals, causing a short circuit.

  • Foreign Objects:

Entry of external substances such as liquids and metal fragments is also a common cause of short circuits. Liquids may be due to equipment leaks or environmental factors, while metal fragments may be due to oversight during maintenance or cleaning. These external substances provide a low-impedance path for the circuit, leading to a short circuit.

Identifying and Dealing with Short Circuits

One of the most common signs of a short circuit is a tripped circuit breaker, causing the circuit to shut down. While this may sometimes be due to reasons such as power overload, the cause of the trip needs to be investigated.

Locate the tripped breaker on the main service panel, typically a switch with a handle, which should be in the off position.

Then, reset the breaker and observe if it trips again. If the breaker trips again, it indicates a wiring issue with one of the devices.

To ensure safety, always shut off the breaker when inspecting circuits to prevent current flow.

Inspect all power lines in the tripped circuit. If damaged insulation is found on any wires, it may indicate a short circuit within a device. In such cases, the damaged device needs to be removed from the circuit.

If any suspicious appliances are found, remove them immediately and reset the breaker to confirm if that point is the fault. If confirmed, the circuit should be able to operate normally. If not, it may trigger another trip.

Systematically investigate each suspicious point until the specific location of the short circuit is confirmed.

During short circuit repairs, it is essential to shut off all power sources and inspect wire connections on outlets. Repair processes may require a professional electrician unless you have sufficient knowledge to do so yourself.

Methods to Prevent Short Circuit Hazards

The primary method to prevent short circuit hazards is to implement appropriate electrical protection devices to reduce the risk of fire caused by current overload. Among these, circuit interruption during a short circuit is considered the most effective. The most commonly used electrical protection devices include fuses and circuit breakers.

Fuse vs circuit breaker

Fuses are traditional electrical protection devices typically made of conductive materials. When the current in the circuit exceeds the rated value of the fuse, it heats up and melts, thereby cutting off the circuit. However, fuse melting is irreversible, and once melted, the fuse needs to be replaced.

In comparison, circuit breakers are reusable electrical protection devices typically installed on the main circuit panel. Circuit breakers have manual or automatic reset functions. When the current in the circuit exceeds the rated value, the circuit breaker quickly cuts off the circuit, preventing current flow, thus providing protection.

With the increasing safety requirements for electronic use, more advanced circuit breakers have emerged, such as ground fault circuit interrupters (GFCIs) and arc fault circuit interrupters (AFCIs). The former can detect current fluctuations more sensitively and immediately cut off the current, while the latter cuts off the power before sparks occur, further improving safety.


Finally, it is worth emphasizing once again that a short circuit is a serious electrical fault. If you suspect that your equipment may be at risk of a short circuit, it is essential to promptly investigate and engage a professional electrician for repairs.

This article was excerpted by TechSparks from online sources and optimized based on our own knowledge and ChatGPT. If there are any copyright infringements regarding the use of text or images, please contact us, and we will promptly make corrections or deletions. If you have more interesting content you’d like to share, feel free to reach out to us!

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