What is overcurrent?(Causes, Effects and Protection)

What is overcurrent?(Causes, Effects and Protection)
overcurrent protection CB

Overcurrent is a destructive fault that can damage small as well as large motors and electric devices. In this article I will discuss current increasing (overcurrent) and answer he most important questions about it. let’s get started.

What does electrical current increasing mean?

Electric current increasing or Overcurrent is exactly what it sounds like: It’s an excessive amount of current or amperage in an electrical circuit. Overcurrent is when the circuit’s rated amperage or the connected equipment (such an appliance) exceeds that circuit’s capacity.

Overloading the circuit or a short circuit, ground fault, or arc fault can lead to an overcurrent. Circuit breakers and fuse protect the wiring from overcurrent damage.

In other words, Overcurrent, or excessive current, is a condition in which an electrical power system has more than it intended. This can be through a conductor. It can lead to excessive heat generation and equipment damage.

The voltage that pushes the current through the circuit and the resistance that blocks the current flow determines the electric current passing through it. Even though circuits are designed to prevent accidents, they can still happen. For example, wires touching each other suddenly.

Electrical circuits have circuit breakers, surge protectors, and electrical fuses to prevent potential disasters. Circuit overload causes the breaker to trip, opening up and shutting off the power supply. This is a great way to avoid house fires. The overload could cause the wiring to overheat and melt, leading to a house fire. It shouldn’t happen often.

What causes current to increase in a circuit?

Possible causes of increase current in an electric circuit.

  • Short circuits
  • Excessive load.
  • Design fault.
  • Arcing in circuits.
  • Loose connection.
  • Voltage drop.
  • And Earth Faults.

Each electric device consumes a certain amount of electric current while operating. However, circuit overload will occur if you use more power than the circuit is designed for, or short circuits occur in the device or any other fault that’s mentioned above. This increases the circuit’s total load resulting in increased current.

Electrical circuits can only handle a limited amount of electric current as per their design. Circuits comprise Cables and circuit breakers (or fuse in the older wiring systems) and other devices (such as lighting fixtures, appliances, and everything that plugs into an outlet).).

Each device’s electricity consumption (when it is running) contributes to the circuit’s total load. The circuit breaker will trip if the circuit’s rated current is exceeded, cutting off power to the circuit.

Why does current increase when load increase?

Electrical loads are typically connected in parallel. If you have a load(impedance) raised, it means the added load is connected parallel with the existing load. Parallel connections always decrease the equivalent impedance. Therefore, the current increases.

When loads are connected in parallel, each load draws its own current according to the requirements of that load. Therefore, the current is increased when the load is increased.

It can be described as a parallel combination of impedances. If impedances are parallel, the effective impedance is less than the least. Therefore, it draws more current.

Simple Example: suppose that a 10 Ohm resistance connects to the battery with 10 V, and the voltage drawn from the load is 1 amp. Increase the load by a further 10 Ohm resistance is put to form a parallel. The total resistance would be 5 Ohm of this combination, and the current flowing from to the terminals of batteries will increase by two amps, so we can say that the load that the current drawn by the load increases.

What happens when an electric current increases?

An overcurrent could cause the circuit wiring to overheat. This could lead to the melting of the insulation and a fire. The heat loss from increasing current can cause damage to the circuit, burn resistors, damage electric equipment or even cause fire to the surroundings.

Circuits are designed to work with a particular voltage and resistance. If the excessive current flow in a conductor, there will be voltage drop occur due to voltage drop there will be less voltage at the load.

This is why we use larger cables to maximize current flow and reduce voltage loss in conductors. The voltage that pushes the current through the circuit and the resistance that blocks the current flow determines the electric current passing through it.

Even though circuits are designed to prevent accidents, they can still happen. For example, wires touching each other suddenly. Electrical circuits have circuit breakers, surge protectors, and electrical fuses to prevent potential disasters. Circuit overload causes the breaker to trip, opening up and shutting off the power supply

 Different circuits have different load ratings so that some circuits can supply more electricity than others. Although home electrical systems are intended for household use, there is no reason to allow us to plug in multiple devices at once.

You can avoid overload by learning more about the circuit layout of your home. Check circuit breaker and other overcurrent protection devices ratings and check wire sizing as well. This is a great way to avoid house fires. The overload could cause the wiring to overheat and melt, leading to a house fire. It shouldn’t happen often.

Although electrical systems in homes are designed for normal use, overloading circuits can occur. To prevent overloads, it’s important to be familiar with the circuits in your home.

Why does the current increase temperature?

The more current in a conductor the higher the temperature rise. The flow of electrons is described as current; As the current grows, the electrons flow will increase. Due to the increased flow, the collision of electrons will intensify, generating heat energy. This is why the temperatures increase when the current increase.

Temperature rises beyond the allowed limits on any device is directly linked to the fact that you have exceeded power consumption higher than the rated value. Any R that is designed to meet a specific power consumption, if the limit is exceeded”R” gets heated, i.e., temp raised.

Also, P = (I*I) *R means that increasing ‘I’ and the ‘R’ (flowing, which was pre-designed for any particular amount of resistance) raises the temperature.

Read also: Electric transformer temperature rise.  and the other article ,Motor temperature rise causes and limits.

Why does increase in current increase power losses?

As you can see from the below equation, the power is proportional to the square of the current. So, if the current increases, the power losses will increase much faster. As we know that Power = I2 × R ,This means that, a greater current means more energy loss in the conductor in the form of heat. As I mentioned above.

The power in a device with resistance, like a conductor, is P=I2 x R, Were P=power in Watts, I=current in Amps, and R=resistance in Ohms.

There is no “Resistive matter. “Each material has a certain resistance to the flow of current in it. When we force current to flow in this material, it heats up.

What is Overcurrent protection?

As clear from the name, the term overcurrent protection is the process of safeguarding an electrical device against the excessive flow of current. The excessive flow of current heat up the device and as a result the device get damaged. Therefore, different measures need to be taken to ensure the safety of a device.

Different overcurrent protection devices are used nowadays. When a large amount of current flows in a circuit, the protective device opens the circuit and as a result, the flow of a large amount of current is stopped.

Difference Between Overcurrent and Overload Protection

Overcurrent protection is protection against excessive currents beyond the acceptable designed current rating of an equipment. It generally operates instantly due to the large current value. Short circuit, arc fault and earth fault are overcurrent types. Some electrical protection devices such as fuses, magnetic circuit breakers and overcurrent relays.

On the other hand overload protection is a protection against a overcurrent that would cause protected equipment (such as electrical motor) overheating. Hence, an overload is also some kind of overcurrent. Slow acting fuses and overload relays are commonly used overload protection devices.

A thermal-magnetic CB as well as the dual element fuse has both thermal and magnetic elements which means that it could provide both overcurrent and overload protection.

Overcurrent Protection Devices

Overcurrent protection is critical to personal safety. Different hazardous conditions can result in materials igniting, making fire, or blasts due to improper overload protection or short circuit protection.

The most popular safety devices include fuses, circuit breakers, and protection relays that detect overcurrent also known as OCPDs. If an overcurrent is detected, the devices cut off the circuits through which current flows, stopping or redirecting the current flow. Every electrical circuit within homes must be protected by an OCPD designed for the wiring in the circuit.

Overcurrent protection devices (OCPD) are an item of equipment employed in electrical systems that are susceptible to experiencing an overcurrent due to short circuits, overloads, and ground faults. Overcurrent refers to any circumstance where the amount of electrical current (amperes) in an electrical system (e.g., in an electric circuit) is greater than the current the system was designed to manage. In the event of an overcurrent, the OCPD will redirect or stop the current flow through the system to ensure that it is secure.

Today, many homes are equipped with circuit breakers situated in the primary service panel, also known as a “breaker box.” Homes that are older and not upgraded may have service panels with fuses rather than breakers. Fuses function the same as breakers, but just like breakers, they need to be sized appropriately for each circuit to guard against overcurrent.

  • Fuses

Fuses are the most commonly used protection devices. We have seen and experienced it so many times that when any disorder happens in the residential electrical system, the fuse blows up. A good fuse always measures zero voltage. while whereas an open fuse reads some value of voltage because the load side is hot.

We can define the fuse in a more specific way. A circuit opening fusible part heats up due to the flow of AC or DC current. Once a current above the rated value flows through the circuit. The fuse blows up and makes the circuit opens and the flow of fault current is topped.

Fuse current carrying capacity: is the maximum current that the fuse can handle without interrupting the circuit.

Fuse breaking capacity: is the maximum current value that the fuse could interrupt safely. It should be higher than short circuit current.

AC and DC fuse as over current protection

As mentioned above that fuses are used for over current protection. This is common in both AC and DC electrical circuits. But always remember the rule”never use AC fuse in DC circuits“. AC fuses in DC circuits is dangerous and could lead to fire situation. DC current is constant unlike AC current which goes to zero several times per each second. So AC arc is easier to extinguish than DC one. This is why DC fuses are longer than AC fuses to help in DC arc extinguish.

For more details read also: Never use AC fuse in DC circuits

Nevr use AC fuse in DC circuits
Nevr use AC fuse in DC circuits
  • Relays

A relay is an electric protection device that is designed to respond to input conditions , after specified conditions are met, to cause contact operation.  Inputs are usually electric such as dc signal, but may be thermal, mechanical, or a combinations of quantities.

In over current protection, we use protective relays. The protective relay detects defective lines and apparatus in the power system and initiates an appropriate control action. Relays are used in high voltage electrical systems.

Protective relays are commonly referred to by standard device numbers. For example, an instantaneous overcurrent is a 50 device while a time overcurrent relay is referred to as a 51 device.

I have written a detailed article about solid state relay, you can read it here.

  • Circuit Breaker

Circuit breakers are another type of protective device. These are switching or automatic protection devices. CBs are used in all electrical applications starting from your home electricity box, small control panels and low and medium voltage switch gears.

  • CB rating

Circuit breakers are rated by different terms such as operating voltage, current level, short circuit interrupting capacity, load specific use or switching, and phases or poles.They are further classified by their tripping characteristics. These are rated for voltages below 1000v. We will discuss a different type of circuit breakers.

  • CB types

There re several methods of circuit breaker classification. The most common used way is the classification by arc extinction medium. Below some CB types briefly.

  • Air circuit breaker. Air is used for arc extinction , This type is common for low and medium voltage applications.
  • SF6 Circuit breaker. The sulphur hexa-fluoride CB uses SF6 gas for extinguishing the arc.
  • Vacuum Circuit breaker. In this type the breaker contacts are placed in a sealed vacuum interrupter.
  • According to number op poles: single, double and three poles CB are used in different applications.
  • GFCI or ground fault circuit interrupter. This is a safety device for human protection against electrical shock. It detects phase to ground faults and interrupt the circuit before a human get shocked.
  • AFCI arc fault circuit interrupter. This type interrupts the circuit in case of excessive current due to arc faults and protect against fire.
GFCI - ground fault circuit interrupter
GFCI – ground fault circuit interrupter

When does/doesn’t current increase with increase in voltage?

The current increase or decrease depending on the component used in the circuit we employ.

  1. If Resistance is fixed, current increases when there is an increase of voltage or the current decreases with a decrease in voltage.
  2. If we hold power constant, the current decreases as voltage increases, or the current rises as voltage drops.

Let’s look at ohm’s Law to understand it in more details:

If the resistance components on the load side are taken with the voltage V.

According to Ohm’s Law, V=IR, we can see that the voltage is directly proportional to current. This means that as the voltage rises, the current will increase, or when the voltage decreases, the current will decrease; if that, the resistance stays identical, i.e., resistance shouldn’t change.

When the source is connected to an electric transformer with a power supply voltage, V.

Then, using the power formula P=VI

Before moving forward, you must be aware that the transformer changes the voltage or alters the current, but the power stays constant, i.e., the power must be consistent.

Then we apply the formula P=VI. Here, with a rise in voltage, the current is reduced or vice versa, yet it remains at the same power.

However, Ohm’s Law always applies. From the above study, we catch that.

  1. If Resistance is fixed, current increases when there is an increase of voltage or the current decreases with a decrease in voltage.
  2. If we hold power constant, like induction motors, the current decreases as voltage increases, or the current rises as voltage drops.

UPS, Battery chargers, Induction heater, UPS, etc. are just a few examples of devices where the current does not increase or decrease in response to a change of voltage. Still, Resistance changes to ensure that the current remains constant.

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