What is electrical short circuit & why is it dangerous?

I can say that electrical short circuit is the nightmare for electricians and us, i.e electrical engineers. Not only equipment damage that electrical short circuit cause, but also it could be destructive and can cause fires.

In my work, We have lost more than 7 generators. I saw complete damaged electrical motors and generators due to short circuit. In many cases the generator catch fire and get completely damaged.

What is an electrical short circuit?

Electricity is divided in two, AC and DC source, In DC systems like batteries there are two poles, one is positive(+), and the second is negative(-), These poles must not touch each other directly in any conditions, because if they do then an electrical short circuit will start.

In AC system like synchronous generators and the plugs in your house, the poles are called phases and one neutral, phases and neutral must not touch each others in any case, also different phases must not touch each others, if this happen this will start a short circuit.

Short circuits produce a huge amount of power and heat, which could melt plastic, copper, aluminum and iron, and could cause damage to the equipment and fire.

Why is electrical short circuit dangerous?

A short circuit is dangerous and could cause fire, devices damage or even human injury and death. This is because its two effects, Mechanical and thermal effects. Its one of the many shapes of electrical hazard.

When a short circuit condition begins a large amount of electrical current passes through the electrical system starting from generator passing through cables and devices of the circuit and ending to the fault location. This current value is in Kilo Ampere which is much larger than normal current.

This kilo ampere current produces high temperature large enough to destroy the faulty device and to melt copper conductors, circuit breakers contacts and almost any thing on its way. This is called, thermal effect of a short circuit.

What is A Bad Effect of a Short Circuit?

Short circuits may cause overheating, fire, and explosions, among other things. All of these things have the potential to cause considerable harm and possibly injury. When a short circuit happens, the system’s current rise to an abnormally high level while the voltage falls to a low one.

Due to the high current generated by the short circuit, excessive heating occurs, which might end in fire or explosion. Short-circuits can sometimes take the shape of an arc, causing significant damage to the system.

For example, if an arc on a transmission line is not rapidly cleaned, it will severely burn the conductor, causing it to shatter and cause the line to be disconnected for an extended period of time.

The low voltage caused by the malfunction has a significant negative impact on the power system’s ability to provide Service. The consumer’s motors may be shut off, and the power system’s generators may become unstable if the voltage is low for even a few seconds.

Because of the aforesaid negative effects of a short circuit, it is desirable and important to disconnect the faulty portion as soon as possible and restore normal voltage and current levels. Due to the tremendous power dissipation in the circuit, short circuits can generate extremely high temperatures. The application can take advantage of the high temperature.

Short circuit has mechanical and thermal effect. Let’s discuss each in more details.

Mechanical effect of short circuit

The current flow during the fault condition in the bus bar has a reverse direction than the normal flow direction. This causes  a repel condition between the faulty bus bar phase and the normal one. This could cause bolts and other parts to fly away in air in dangerous condition.

Why does a short circuit cause fire? (thermal effect)

When current passes through an electrical conductor it causes a rise in temperature. This rise depends on the conductor resistance and the current value. Th larger the current value the higher the temperature. As mentioned above that the temperature rise is one of two main factors which are the answer of the famous question, Why is a short circuit dangerous?

If the protection device fail to isolate power of faulty load, Then the current of the SC could be very high and produce more and more temperature rise. This rise is enough to cause fire

What are causes of short circuit?

Many causes of short circuit in all electrical equipment, and in all fields of work, but in general electrical wires, cables and all current carrying electrical conductor by default are isolated or at least are separated from other conductors.

If, for any reason, the different phases in AC circuit get touch together or get touch to ground, a short circuit situation occurs.

So in simple words, the main reason of electrical short circuits is insulation failure between phases or between phases and neutral.

What makes the insulation to fail?

To understand the main reason of insulation failure we should first know that the insulation of electrical devices, wires and cables is a layer or multi layers on the conductor, this layer is made of PVC or XLPE and has temperature limits i.e any rise in temperature will cause insulation to fail.

  • Now we know that excess heat damage the insulation layer, also mechanical damage and manufacturing issues would weaken the insulation causing it to be damaged.
  • Over-current is also one of the main reasons of short circuit, this is because over-current generates more heat in the conductor.
  • Human faults may be one of the short circuit causes, as any accidental connecting different phases to each others or to neutral will cause a short circuit.

Most common causes of short circuit

Faulty Circuit or Wire Insulation

Faulty circuit or wire insulation is the first reason. Because sometimes cable core becomes damage with the passage of time.

The inner wire material is exposed, due to which old wires allow the hot and neutral wire to touch each others, this causes a short circuit condition.

The life span for a cable is up to forty years. Another reason is, sometimes fault occurs in a circuit. Sometimes faulty appliances like faulty power cord, faulty plug, or a flaw cause short.

Loose Wire connection

To keep the current flowing in the circuit, strong connectors are always needed. If the connector becomes loose, there is a chance for the electricity to pass to the neutral wire or a grounded part of the circuit.

This phenomenon also becomes the causes of short circuit. To avoid chances of short circuit the faulty wire connection needs to be inspected and fixed. However, the handling of faulty wiring is a tricky job and is best handled by an expert technician.

Faulty Appliance

If we plug an electrical appliance in the plug. If there is a fault in a device the current flows can cause a short circuit immediately.

Human faults

Some times humans make mistakes while working on electricity and power cables. Some mistakes are because some electricians are not following HSE and electrical safety procedures and electrical isolation and LOTO system. These mistakes could cause electrical connection between two different phases causing electrical short.

Using not isolated hand tools could accidentally connect tow phases directly causing short. So, its important for each electricians to apply proper isolation lockout and tag out (LOTO) system. And also use proper isolated hand tools. 

Types of short circuit

  • Phase to phase
  • Phase to neutral
  • phase to ground

Protection against electrical short circuit

As mentioned above short circuit is dangerous and must be taken into account when designing any electrical system. The protection devices are fuses, circuit breakers and advanced protection relays.

Fuses and circuit breakers are mostly used. While protection relays are used in industrial loads and switch-gears.

  •   Before failure

Keeping electrical devices, motors, transformers, and equipment safe needs a good preventive maintenance program and periodic electrical  inspection, in this electrical maintenance program you as an electrical engineer or electricians should take periodic readings for temperature and insulation resistance and compare them with the manufacturer recommendations.

Train your staff

All electricians should be well trained to apply proper isolation lockout and tag out (LOTO) system. And also use proper isolated hand tools. This way we could prevent and avoid serious faults and human injury.

  • During failure

Electrical protection devices are so smart today, and could detect a short circuit of hundred and thousands of amperes, and are apple to isolate and stop the defected device and protect it before the short circuit cause total damage and fire.

DC and AC fuses, miniature circuit breakers (MCB’s), molded case circuit breakers (MCCB’s), and advanced protection relays are used to protect electrical panels, motors, transformers, and also switch-gears against any possible short circuits.

What to do in case of short circuit?

If you are not an electrician or electrical engineer. Then dealing with short circuit need to be focused. If a circuit breaker trips instantly this is a strong indication that the circuit breaker tripping is due to a short in the circuit not due to overload. Follow the below steps in case of your breaker trips instantly.

  1. Switch off all devices and appliances which are affected by the tripped breaker.
  2. Check your electricity box and find the tripped breaker. It should be on the off position.
  3. Switch on the circuit breaker.
  4. Turn on all devices one by one. The faulty device will cause the breaker to trip instantly as you turn it on.
  5. Call electrical inspection service to check this device for you.

Can A Short Circuit Damage a Breaker?

Of course, A short circuit can badly damage the circuit breaker because of its thermal and mechanical effect. Circuit breakers are built to shut in the event of an overload or short circuit. However, there’s a possibility that they may fail without triggering, which could cause more electric damage that could be caused to your breakers box or appliances within your home.

Your electrical system has short-circuited protection in the form of circuit breakers. When electrical currents are judged unstable, these components in your electrical panel shut down, with each one connected to a distinct circuit. We recommend that you do some simple circuit breaker maintenance to ensure proper operation

Circuit breakers are available in a variety of types and sizes. Nearly all circuit breakers for residential use are low-voltage. A residential building, for instance, could have a medium voltage circuit breaker. At the same time, a High-voltage circuit breaker is used by utilities that provide electricity to the entire city.

Short circuit currents are too large, and able do make huge damage to any electrical circuit device, the value of this current depends on many things like the load power, voltage level and circuit design, the main job of the protection device is to isolate the damaged part of the circuit as fast as possible.

Each protection device is designed to handle a certain short circuit current value, if the fault current is less than this value then the device will be able to isolate the faulted device, but if the current value is larger than the designed one then the protection device it self will be damaged.

Short circuit case study

The images below are in my workplace. A damaged synchronous generator due to short circuit. The winding of the generator was short circuited and completely damaged as fire started inside it. The main cause of this short circuit was the moisture.

In a foggy day the moisture entered into the windings, causing the insulation to decrease and the short circuit to happen. It happens here all the time.

You may ask, How can the moisture enter the generators? Well, its all about the IP rating of the generator. Simply its not suitable for working outdoors. Its somebody’s mistake here. I really don’t know who is this guy, I mean the guy who made the purchase order of low rating IP generators for outdoors working. The case is the case. We have to deal with this situation one way or another.

electrical short circuit damage
electrical short circuit damage

What Happen to Current in Short Circuit?

Because the source of electrical current has been diverted from its regular flow direction, it encounters little or no resistance when a short circuit happens. As a result, excess heat is produced, which can damage electric equipment. If a fuse is present in the supply circuit, it will blow out, opening the circuit and interrupting the current flow.

To dive deeper into the simple technique to compute short circuit current calculations, we must first brush up on the fundamentals of short circuit analysis. The Short Circuit Current is analyzed to determine the intensity of the short circuit’s current and compare the short circuit’s current with the interrupting capability of devices to prevent overcurrent’s. According to a fundamental electrical theorem, the short circuit current is determined by critical parameter:

According to Ohm’s law


The load is bypassed when there is a short circuit, and resistance becomes zero.

Then I =V/0;

As a result, the current in case of a short circuit is ideally infinite. But, as you can see, there is still considerable resistance in the wire between the voltage source and the point of failure. So, instead of infinity, the short circuit current goes to kilo Amps values. These values are destructive.

We may State that a large quantity of current travels through the circuit. How high is it? This is determined by the voltage level at which the short circuit occurred, the distance between the problem and the source, and the cable used in the wiring.

What Happens to Voltage in Short Circuit?

Throughout a short-circuit circumstance, the voltage in between two points in the circuit excluding the source turns ZERO, and the reason for this is that the load becomes zero, or the circuit is not linked to any form of load. As a result, it draws a massive amount of current, and the voltage drops to ZERO.

I understand your skepticism! Allow me to explain both conceptually and practically.

Keep in mind Ohm’s Law: V = IR.

The current across the conductor is at its highest during a short circuit. The conductor’s resistance is as low as 0. How? Continue reading below.

Consider a copper wire with a thickness of 20 AWG used for standard house wiring. The resistivity of such a copper wire is 33.2 ohms per 1000 meters, or 0.00332 ohms if the wire is one meter long. As a result, the resistance of the conductor is regarded zero, while in practice, it is minimal.

Your power supply is protected by a fuse. A 5A/15A fuse may safeguard the entire house. During a short circuit, current flows through the conductor until it reaches the value I = V/R, where V is voltage and R is the resistance of that conductor. Because R is nearly 0, the current will grow to infinity (ideally, but remember it’s 0.0032, not 0 ohms)!

But the fuse will not let it happen.

Assume you have a 15A fuse and a maximum load current of 15A for your devices. Consider your gadgets to have 1-meter copper conductors. Using the copper wire indicated above, during a short circuit, the current will begin to rise to infinity before breaking the fuse. In such a conductor, the maximum current will be 15A. That wire’s resistance will be 0.0032 ohms. As a result, the voltage across a short circuit wire is V = IR = 15 * 0.0032 = 0.048 Volts. As a result, the voltage in a shorted wire is deemed zero.

What Happens to a Battery if Short Circuit Its Terminals?

It will overheat, leak, and potentially explode the battery. If the battery can generate a high current, it can induce overheating of the wire or other object shorting the terminals, posing a burn/fire hazard.

When you externally short-circuit a battery, internal resistance restricts the current. The short circuit current will be little if the internal resistance is high.

The internal resistance of older, non-rechargeable batteries is often high. The internal resistance of the carbon-zinc battery you linked to is likely to be high.

Internal resistance is meager in compact lead, NiMH, and lithium-ion/polymer batteries. If you short one out, you can get a huge spark and a lot of heat. So, don’t short any of these batteries!

One more thing. The electromagnet wire does have some resistance. As a result, the short circuit current will be considerably restricted.

What is difference Between Short Circuits and Open Circuits?

When no current is taken or supplied, the open-circuit voltage is the voltage difference measured between two terminals. The current that flows when the terminals are forced to have a zero-voltage difference is referred to as short circuit current.

A short circuit indicates that the two ends are linked externally with resistance R = 0, the same as an ideal wire. This signifies that no voltage difference exists for any current Value. (Remember that actual cables have a resistance that is more than zero!)

An open circuit means that the two terminals or points are outwardly unconnected, which corresponds to a resistance R =∞ This implies that regardless of the voltage differential, no current can pass between the two terminals. (It should be noted that very high voltages can induce current arcs to flow even through vast air or vacuum gaps!)

What is Difference Between Short Circuit and Ground Fault?

A short circuit is an improper connection between two nodes of an electric circuit that are supposed to have different voltages. When a “hot” conductor makes contact with a neutral or ground conductor, it causes arcing. A ground fault occurs when an electrified conductor comes into contact with the ground or the equipment frame.

A ground fault is a sort of defect in which the stray electrical current passes unintentionally to the Earth (to the ground).

Because the circuit is “short,” in this case, it has bypassed the circuit wire; a ground fault is technically a sort of short circuit. And, as with any short circuit, the immediate effect is a dramatic decrease in resistance, allowing current to flow unhindered.

A ground fault, like other forms of short circuits, causes the circuit breaker to trip owing to the uncontrolled flow.

A short circuit is an electrical flow that escapes from its designated circuit with little or no resistance. The most common reason is bare wires contacting one other or loose wire connections.

The initial effect is that a considerable amount of electricity starts to flow. As a result, the circuit breaker trips, immediately stopping all current flow. This is referred to as a “short” circuit because the current bypasses the entire circuit wire and returns directly to the source via a shorter path.

Does Grounding Prevent a Short Circuit?

Grounding is not a way to prevent the short circuit from happening. It is a way to recognize an unbalanced circuit.

Earthing is generally used to stop the harm to our bodies and domestic appliances. When the voltage goes through electrical wires, our appliances may be damaged.

In addition, during the time of lightning on the horizon, a metallic rod is attached to heavy metal plates beneath the house’s structure. So, more current neutralizes the earth.

How short circuit blow a fuse?

The large value of current passing through the fuse during the short circuit, makes its element to heat up and blow.

The element of the fuse is designed for currents much lower than the short circuit currents. This value depends on Its material and cross sectional area. The thermal effect of the short circuit current is capable of blow the fuse element so easily.

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