What is Short Circuit and Why is it Dangerous?

Electric power systems in industrial plants and commercial and institutional buildings are designed to serve loads safely and reliably. An electrical short is a dangerous phenomenon. Below I will explain the definition of the short circuit in simple terms and you will exactly understand what it is.

What is Short Circuit in Electricity?

The short circuit is an overcurrent produced by a minor impedance fault between conductors with different potentials. It is accidental and can be due to clumsiness or an equipment defect.

The short circuit is dangerous because when a short circuit occurs, the resistance of a circuit drops to almost zero ohms. This increases the current quickly and heats the conductors or equipment.

A short circuit is usually caused by accidental contact or worn insulation. A short circuit is more dangerous than an overload because the damage occurs almost instantly. Examples of short circuits include two or more conductors accidentally touching, someone touching or dropping tools across energized conductors, or an accidental connection between energized conductors and the ground. Such ground faults may vary from a few amperes to the maximum available short circuit fault current.

Protection devices must be provided to limit and break the short circuit currents before their thermal (heating of the conductors, electric arcs) and mechanical (electrodynamic forces) effects become harmful and dangerous. Protection against short circuits can be provided by fuses and circuit breakers. Their breaking capacities and circuit opening times must be suitable for the circuit being protected.

Why Short Circuit is Dangerous?

When a short circuit occurs electrical current can be hundreds to thousands of times greater than the normal operating current. A high-level short-circuit may be up to 30 kA or 200 kA. It can have serious negative effects.

The short circuit must be interrupted as quickly as possible to minimize the damage which can include:

• High magnetic forces that warp and distort busbars and associated bracing beyond repair.
• Severe insulation damage.
• Melting or vaporizing conductors.
• Vaporizing metal, including busbars in electrical equipment.
• Ionized gases.
• Arcing fires.
• Explosions.

Can a Short Circuit Kill You?

A short circuit can kill a human. In a short circuit, the current bypasses the normal load. Short-circuit currents may vary from fractions of an ampere to 200,000 amperes or more.

How Does a Short Circuit Cause a Fire?

A short circuit is usually created when a low-resistance wire is placed across a consuming device. A greater number of electrons will flow through the path of least resistance rather than through the consuming device. A short usually generates an excess current flow in the cables which results in overheating, possibly causing a fire.

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