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, electric devices and home appliances.

In this article I will discuss current increasing (overcurrent) and answer he most important questions about it. let’s get started.

what is overcurrent?

Overcurrent, refers to any circumstance where the amount of electric current in an electrical system is greater than the current the system is designed to manage.

Electric current increasing or Overcurrent is exactly what it sounds like: It’s an excessive amount of current or amperage in an electrical circuit.

Overloading the circuit, a short circuit, ground fault, or arc fault can lead to an overcurrent.

Overcurrent example

A clear overcurrent example is, when a motor with rated current 35A, you can find rated current on the motor nameplate, draws 55A for any reason, it can be a mechanical loading as I discussed in the article Motor Overcurrent, this motor is an overcurrent situation.

Another example, If a current of 167A passes through a cable with current ampacity of 135A, this cable is over current situation.

In general, any electrical equipment has a rated current, whenever the current exceeds this value, its an overcurrent situation.

Overcurrent effects

overcurrent effect on a contactor
overcurrent effect on a contactor

Uncontrolled electric overcurrent leads to excessive heat generation and can damage or burn equipment.

A circuit wiring overheats when an overcurrent occurs. There is a possibility that the insulation could melt, and a fire can break out as a result.

Circuit overload causes the breaker to trip, opening up and shutting off the power supply. The overload could cause the wiring to overheat and melt, causing a short circuit and leading to a house fire.

In addition to the heat loss from increasing current,  the rising current can also:

  • Damage the circuit
  • Burn resistors and electronic components
  • Damage electric equipment and home appliances
  • And even cause fire to break out around the circuit.

What causes overcurrent in a circuit?

Possible causes of overcurrent 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, the reason doesn’t matter, the overcurrent effect is the same.

Circuit’s overloading

When a circuit is subjected to an overcurrent, a circuit overload takes place.

The breaker will trip if you’ve overloaded a circuit by plugging too many appliances into one socket. A surge power draw is another typical sort of overload.

This occurs when a motor, like the compressor in a refrigerator, needs a lot of electricity to start up.

Short Circuits

In a short circuit, a “hot” wire touches another “hot” wire or touches a neutral wire.

There is a lower resistance along the short circuit path than along the normal path of the circuit, allowing a lot of currents to flow, resulting in excessive wire heating.

I have written a detailed article about short circuit, you can find it here for more information.

Ground Faults

When a hot wire comes into touch with a grounded item, such as the metal casing of a tool or appliance or an electrical box made of metal (when placed as part of a grounding system), a ground fault frequently results.

For more information about electrical grounding, read my article here.

Arc Faults

Electric discharge leaps from one conductor to another is called an arc fault.

This can occur when a hot wire meets a neutral or ground wire or when a hot wire has a minor break and only occasionally makes contact.

Loose Connection

Arcing can also be brought on by a loose wire connection on an outlet or other equipment.

High current flow and intense heat are produced by arc faults due to loose connection, which can melt wire insulation or cause fires.

How can you prevent over current?

Electrical circuits have circuit breakers, surge protectors, and electrical fuses to prevent potential disasters.

The concept of preventing a power outage due to an overcurrent is quite straightforward: you should avoid overloading a circuit in the first place.

There are typically separate circuits for each room of the house, with heavy-duty appliances like an electric dryer or oven requiring a separate dedicated line.

In order to prevent your circuits from overcurrent, let us take a look at how you can do it.

Your circuit load should be calculated

For workplace, never run any power tool or electrical equipment before you check its power rating, and verify the power source is suitable for it.

Only authorized persons are allowed to add new loads to any power source.

All authorized departments should participate when choosing a new equipment. For example, when choosing a new pump, electrical and mechanical engineers should cooperate to make sure the pump and the motor ratings are the same, to prevent motor overloading.

For home circuits, majority of circuits are rated for 15 to 20 amps, and if you understand how much current your lights and appliances use, you can roughly estimate how much current is safe to put in.

It may be necessary to move the light strand to another room if your load is approaching 80% before plugging in the next strand to avoid overcurrent.

  • Never use extension cords without asking an authorized electrician.
  • Never overload the outlet with a lot of appliances.
  • Ask for advice before connecting any new appliance.
  • If you buy a new house, hire an authorized electrician to check its circuits and wiring.

Use large appliances with caution

When searching for a location to plug your lights in, it’s a good idea to stay away from spaces that already include a lot of equipment, such as the kitchen.

To make more current available for those priceless decorations, you may disconnect any equipment or devices you don’t intend to use to avoid overcurrent.

Make LED lighting a priority

Investing in LED lights is one method to make your current setup considerably more festive.

LED lights consume significantly less power than conventional bulbs, saving you money on your electricity bill and easing the pressure on your wiring to avoid overcurrent.

Use Protection devices

The built-in defense against overcurrent in your home is the circuit breaker. They are housed in your electrical panels and turn off electricity to particular areas of the structure if they detect erratic electrical currents.

You may protect yourself against short circuits, when necessary, by doing routine circuit breaker maintenance to make sure it is operating correctly.

Why does current increase when load increase?

Each load requires its own current, the more the connected loads, the higher the current they draw. To explain it to you, suppose the electrical circuit as a pipe line, the loads are faucets, the more faucets you open the more water you draw.

In case of electrical Motors

In case we have a motor (the load), this motor requires electric current depending on its power rating.

If the motor starts with no load, it draws no load current, it’s smaller than full load current.

By increasing the mechanical load, the motor needs to provide more torque to overcome this load, and of course, it will draw more current.

In case of home loads

In case of connecting more loads on home or a building outlet. Electrical loads are typically connected in parallel.

If you have a load 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 from the circuit according to the requirements of that load. Therefore, the current increases when the load is increased.

How can I tell if my electrical panel is overloaded?

If your panel main circuit breaker trips, and when you turn it on again it works for a while then trips again, its a clear sing of possible overloaded panel.

But, keep in mind that there are other reasons of circuit breaker tripping, you can hire an electrician to measure the currents of the panel, check the man circuit breaker rating and make sure its overloaded.

If you know how to use current clamp, you can measure the current by it, check the circuit breaker rating and make sure the CB rating is greater than the measured one.

Make sure to switch on all loads during the measuring process, this is the only way to have a clear idea about the panel load.

One more thing, an electrical engineer can calculate the panel loads, check the circuit breakers ratings and make sure its not overloaded.

It’s crucial to watch out for clues that your electrical panel could be generating an excessively high level of electricity when you start putting in more and more appliances for any reason.

To assist you in recognizing when this could be happening, we’ve listed a few telling indications.

Panel Overheating, the overheating that might result from excessive current flowing through your breakers or cables is also a sign of overloaded panel.

In my workplace, we use thermal imaging to check that panels are not overloaded.

What happens when an electric current increases?

When the electric current increase, the following points can happen:

In case of electric motors

The higher the current, the higher it temperature rise. This temperature increase can cause the motor insulation to fail, and lead to internal short circuit between windings and a complete damage if the protection device fail to trip the circuit.

In case of home wiring

Excessive current trips the circuit breaker of your home panel. Of course, it will increase the temperature of the wiring, the panel and the circuit breaker.

If the increased current is caused by an appliance, the appliance will get damaged if the CB fails to trip.

In case of electric cables

Cables temperature rise can cause the insulation to get damaged. When the insulation get damaged, the live phase and the neutral or another phase will get in tough and a short circuit happens.

In case of electric generator

electrical short circuit damage
Damaged generator in my work

The generator will heat up, its winding insulation will melt and a short circuit occur between its phases. Yep, its a complete damage.

We can say, an overcurrent could cause the circuit wiring, as well as the electrical equipment to overheat. This could lead to, equipment damage or melting the insulation and a possible fire.

The heat loss from increasing current can cause damage to the circuit, burn resistors, damage electric equipment and home appliances 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, the results will be very bad if the protection device fails to trip the circuit.

Why does the current increase temperature?

From physics point of view

Electric current is the flow of electrons in a conductor. As the current increase, the electrons flow will increase.

Due to the increased flow of electrons, the collision of electrons will intensify generating heat energy and power losses. This is why the electric current increases the temperature.

From electricity point of view

any conductor has a resistance, when current flow through the conductor it faces its resistance.

From the power equation we have,Power = I2 *R, which means that increasing ‘I’ and the ‘R’ increases the power loss in the shape of heat and raises the temperature.

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 equipment is designed to meet a specific power consumption, if the limit is exceeded its power, it gets heated.

ِAny electric current value causes produces temperature, the more current in the higher the temperature rise.

Starting from the equipment rated current, to overcurrent ending at short circuit current. All these currents produce heat, the value of the temperature rise deffer from one current to another. 

Read also my article about Electric transformer temperature rise.  and the other one ,Motor temperature rise causes and limits.

Why does increase in current increase power losses?

Power loss is a result of the conductor resistance which the current faces while passing through the conductor.

As you can see, from the below power loss 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, Power = I2 × R ,This means, the higher the current the higher energy loss in the conductor in the form of heat. As I mentioned above.

The increase of power loss in the conductor increases the conductor temperature. We don’t have ideal conductor with zero resistance, if we do its power loss will be zero.

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 heats up the device, and as a result the device gets 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.

Over current protection importance

In order to keep yourself and others safe from many risky situations, overcurrent protection is important.

Every electric circuit must have circuit overcurrent protection. If the current levels of an electric circuit exceed the safe limits for which they were built, the circuit may be harmed or even destroyed.

Circuit wires may become too hot if there is an overcurrent. In turn, fire and the insulation melting might result due to this situation.

There may be serious consequences if a circuit is not equipped with overcurrent protection. An electrical shock, fire, or electrocution can result from overcurrent, which can destroy unprotected electronic devices and cause human injury and fatality.

The purpose of overcurrent protection device is to protect against dangerously high temperatures in conductors or their insulation. It is crucial to match the conductor size and current rating of the protection device.

We can say, overcurrent protection is essential because it protects humans and equipment as well against destructive and fatal accidents.

Is over current protection and surge protection the same?

NO, it’s different; overcurrent protection protects the excessive current flow in the circuit, and surge protection protects against excessive voltage or spikes of voltage to the circuit.

Overcurrent protection is the protection against excessive currents beyond the acceptable current rating of the equipment. It generally operates instantly.

Magnetic circuit breakers, fuses, and overcurrent relay commonly provide overcurrent protection.

High and low-voltage power distribution systems, as well as control systems, frequently incorporate overcurrent protectors.

On the other hand, Surge protection protects equipment against power surges and voltage spikes while blocking voltage over a safe threshold.

When a threshold is over rated voltage, a surge protector shorts to ground voltage or blocks the voltage.

Low-voltage power distribution systems frequently utilize SPD, sometimes referred to as surge protector, lightning protector, and lightning arrester, as a lightning protection device.

It is often linked to the line in parallel or series to discharge the wave.

Difference Between Overcurrent and Overload Protection

Overloading an equipment causes it to draw an overcurrent. We, electrical engineers, usually use the word overload in case of the equipment gets more load, electrical or mechanical, than its designed to handle.

For example, a motor is overloaded means its mechanical load is greater than the motor rated power so, it draws an overcurrent.

Another example, when a cable is overloaded, it means the cable load, electrical load, draws current greater than the cable current carrying capacity, so the cable has over current passing through it.

Overcurrent protection is, the protection against excessive currents beyond the acceptable designed current rating of an equipment or an electric device.

Short circuit, arc fault and earth fault are overcurrent types.

On the other hand, overload protection is a protection against overloading an equipment that causes it to face an overcurrent situation, and would cause protected equipment to overheat.

A good designed circuit and periodical inspection of loads can help preventing overload

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.

Overcurrent protection devices (OCPD) are items of equipment employed in electrical systems that are susceptible to experiencing an overcurrent due to short circuits, overloads or ground faults.

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.

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.

For more information about fuses, read my detailed article here.

  • protection Relays

protection relay
protection relay

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.

  • 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

When choosing a circuit breaker for overcurrent protection purpose, you should choose the right CB type and rating.

Circuit breakers are rated by different terms such as operating voltage, current level, short circuit interrupting capacity, load use or switching, and phases or poles.

They are further classified by their tripping characteristics. I discussed different type of circuit breakers in my other article here.

How does overcurrent protection work?

According to the circuit current rating of equipment or circuit, overcurrent protection devices have a current rating.

In case of any fault, when the circuit current exceeds the rating current of protection devices, it cuts the circuit’s supply, by the thermal or magnetic effect of the overcurrent. As you know, current has both thermal effect, and if the current passes through a coil it will produce a magnetic effect.

The thermal effect can melt a fuse to protect the circuit, and can trigger the mechanical mechanism of a circuit breaker to trip the circuit.

The magnetic effect also can trigger the circuit breaker faster than the thermal effect. By using this working principle, overcurrent protection devices protect equipment or circuit.

The thermal effect is used for overload protection, lower values of overcurrent, while the magnetic effect, the faster, is used for protection against the short circuit over currents.

Fuse and circuit breakers are overcurrent protection devices that contain time/current characteristics (TCC) that specify how long it takes to clear the fault for a specific value of fault current. The higher the overcurrent value, the faster the tripping time of the circuit breaker.

The fuse’s metal strip or wire melts when too much current flows across it, cutting off the current flow. Fuses are sacrificial components, which means an overcurrent destroys them.

On the other hand, circuit breakers turn off when they face any fault or a short circuit, unlike fuses, which melt to break the circuit. Circuit breakers can therefore be reused.

Can overcurrent damage overcurrent protection device?

Yep, overcurrent can damage the protection devices when the fault current flows due to a short circuit or fault is much greater than the rated short circuit current of the protection device.

Breakers, or fuse cut off the circuit supply. If the circuit breaker short circuit current is greater than the fault current it will safely trip, otherwise it will get damaged.

If we use a fuse as a protection device, then the fuse is designed to blow in the circumstances of the fault, we can say that in case of overcurrent they destroy itself when too much current flows through it and save the connected circuit.

If you install a fuse and switch on the circuit breaker without clearing the fault, your fuse blows again, and the circuit breaker becomes bad due to dealing with fault again and again.

Yep, overcurrent can damage all kind of electrical protection, control and sensing devices.

On of the main protection devices specs is how much short circuit current it can trip safely with out being damaged.

The value of the short circuit overcurrent of a circuit should be calculated during the design phase of the electrical system, depending on this value, we choose the protection devices ratings.

Can over current damage a circuit breaker?

No doubt, it is true that circuit breakers can be damaged by overcurrent. The purpose of circuit breakers is to trip when there is an excessive flow of current as a result of a fault within the circuit.

There are a variety of reasons why a circuit breaker may get damaged, like too old circuit breakers, breakers that face fault conditions many times, breakers that work on full load for a long period, and breakers that are facing too much switching.

Still, one of the most obvious reasons is the short circuit overcurrent, because of the infinity of current flow through the circuit when it occurs. Hence, it damages the circuit breaker a result.

Circuit breakers are usually damaged whenever there is an overcurrent flow due to a short circuit fault.

FOr more information about Why circuit breakers go bad, read my article here.

What if an over current protection device is oversized?

If you utilize an oversized overcurrent protection device that allows current flows greater than the protected equipment’s rated ampacity, the equipment temperature will increase in case of any overcurrent, and it may get damaged before the overcurrent protection device trip the circuit.

Besides, cables feeding the equipment will suffer insulation damage due to temperature rise, which will cause it have a short circuit.

Because protection devices are intended to trip the circuit and stop the flow of electricity if the current exceeds a certain threshold, circuit breakers and fuses rating should be suitable to the equipment it should protect.

Every circuit in your home has a circuit breaker chosen to stop current flow when it exceeds the rated ampacity of the smallest conductor on each circuit.

Let’s have a practical example, If we have a washing machine, the rated current of the machine is 25A, roughly example, if we use a circuit breaker or a fuse of 63A to protect this machine against overcurrent, the machine will, for sure, burn if it draws a current of 35A, i.e overcurrent.

The point is, the circuit breaker or any other overcurrent protection device tripos only currents that exceeds its rating, 63 A in our example, any other current lower than this rating value is a normal current in the eyes of the protection device.

What if an overcurrent protective device opens slower than expected?

If an overcurrent protective device opens slower than expected, it can cause damage to the circuit or equipment.

In case of a short circuit, when too much fault current flow and protective devices fail to stop the current on the suitable time, it can cause damage to circuit wiring, equipment and rupture or explode the protective device while attempting to stop fault currents beyond their tripping ratings.

This will happen when you use substandard or low-quality overcurrent protection devices or expire devices which recommended need to be replaced but you don’t.

Or, you set the response time to the fault current is not small enough. Each overcurrent protection device has a current rating and trip curve, the curve gives you information about the speed of the device to trip the fault current.

The higher the current value, the faster the device should be, that’s why we, some times, refer to the curve as the reverse curve.

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