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What is Over Current Relay? Working Principle and Use

Overcurrent monitoring relay
Overcurrent monitoring relay

An overcurrent relay or overcurrent monitoring relay is used in many different applications today, including commercial power systems, industrial buildings, and other facilities. Below, we take a look at what an overcurrent monitoring relay is, how it works, and some of the different types that are available on the market

What is Overcurrent Relay?

An overcurrent monitoring relay, as its name directly implies, is a device that monitor’s the current flowing through a conductor or device, and reacts if the current exceeds a predetermined threshold. Overcurrent relays are used in many different applications and systems in order to help protect against electrical faults.

The electrical faults include short circuits and overloading. Overcurrent relays can provide protection against all of these faults by detecting when the current exceeds a safe level and then either automatically disconnect the circuit or sending a signal to another device that will take action to protect the circuit.

Ideally, this type of current relay consists of two main components: a sensing device and a control device. The sensing device is used to detect the current flowing through the circuit, while the control element determines the tripping current, usually based on user settings.

Using an overcurrent monitoring relay in a power system
Using an overcurrent monitoring relay in a power system

Overcurrent Relay Function

The main overcurrent relay function is to protect circuits and electrical devices from the damaging effects of too much current. When an overcurrent situation is detected, the relay trips or opens the circuit, thus preventing damage to the electrical components.

Overcurrent events cause wires to overheat and melt, or they can damage sensitive electronic components. In some cases, an overcurrent can even cause an electrical fire.

By tripping the circuit when an overcurrent is detected, the overcurrent relay prevents this damage from occurring. This function of the overcurrent monitoring relay is vital in many different applications, as it can save lives and protect against the loss of expensive equipment.

Overcurrent relay applications include transmission and distribution networks
Overcurrent relay applications include transmission and distribution networks

Overcurrent Relay Applications

Overcurrent relays are used in a variety of different applications, both commercial and industrial. Usually, the relay is used alongside other electrical protection devices, both for current and voltage overloads. Some of the most common overcurrent relay applications include:

Overcurrent Protection for Motors

Overcurrent monitoring relays are often used to protect motors from damage due to high currents. When a motor is overloaded, it can draw too much current and overheat, which can cause damage to the winding insulation. By utilizing an overcurrent relay switch in the circuit, the relay can trip the circuit if the current gets too high, thus protecting the motor from damage.

Overcurrent Protection for Transformer

Overcurrent monitoring or overcurrent protection relays are used to protect transformers from damage due to high currents as well. In these applications, the relays are usually set to trip at a lower current than what is required to trip the circuit breaker. This way, the overcurrent relay trips first and protects the transformer from damage.

Overcurrent Protection for Distribution Lines

Overcurrent relays are an inexpensive solution when it comes to protecting distribution circuits from damage due to high currents. In many cases, the overcurrent relay is the only protection device that is installed in the circuit. The relays may be used to protect against ground faults, phase to phase faults, or phase to ground faults.

Advantages and Disadvantages of Overcurrent Relay

Like all electrical devices, overcurrent monitoring relays have both advantages and disadvantages which make them more or less suitable for different applications. When deciding whether or not to use an overcurrent relay, it is important to consider both the advantages and disadvantages.

Advantages of Overcurrent Relay

One of the major advantages of overcurrent relay use is that it can help to protect against electrical faults by quickly removing the source of the current. This can help to prevent damage to equipment and reduce the risk of fire.

Another advantage of overcurrent relays is that they are relatively simple devices, which can make them less expensive than many other types of electrical protection devices.

From being used as a motor current monitoring relay to transmission line protection and other applications, the current relay finds use in many different settings. This makes them versatile protection devices in different power systems.

Disadvantages of Overcurrent Relay

Apart from benefits, there are several disadvantages of overcurrent relay applications that every electrician or facility owner should know about. One of them is that relays can sometimes cause false trips, which can lead to unnecessary downtime.

An overcurrent relay may not, also, provide adequate protection against all types of electrical faults. When using one, therefore, it’s common practice to install it alongside other essential protection devices.

Overcurrent Relay Price

Overcurrent relays are relatively inexpensive devices, with prices starting at around $20 given their simplicity. However, the overcurrent relay price will usually vary on the market. Their cost mostly depends on the features and capabilities included in the design.

For example, more sophisticated overcurrent relays that offer greater protection against electrical faults can cost more than $100.

Regardless of price, though, overcurrent relays can be a valuable addition to any electrical system, providing an extra layer of protection against faults.

Overcurrent monitoring relays are widely available from many different suppliers and manufacturers. That said, you may want to consult with an electrical engineer or other expert to find the best overcurrent relay for your specific needs.

GEYA GRI8 current monitoring relay echnical parameter:

 GRI8-01GR18-02 GR18-03 GRI8-04
Function                               Over curren Under currentOver Under curren Over/Under current
Supply terminalsA1-A2
Rated supply voltage                           AC/DC 24V-240V
Rated supply frequency50/60Hz,0
Burden                                             max 25VA
Supply voltage tolerance-15%;+10%
Current range                0.05A-0.5A0.1A-1A0.2A-2A0.5A-5A0.8A-8A1.6A-16A
Current frequency                                   AC 50Hz
Max.operating current   1A2A5A8A12A  22A
Current adjustmentpotentiometer
Time delay                                     adjustable 0.1-10 s
Power up delayadjustable 0.1-10 s
Supply indication                                 green LED
Setting accuracy10 %
Repeat accuracy                                      <1 %
Temperature dependancy<0.1%/°℃
Limit values tolerance                  5%(10%for 0.05-0.5Arange)
Hysteresis5 %
Temperature coefficient               0.05%/C,at=20°℃(0.05%F,at=68F
Current rating                                      10A/AC1
Switching voltage250VAC/24VDC
Min.breaking capacity DC                             500mW
Output indicationred LED
Mechanical life                                       1×107
Electrical life(AC1)1×105
Operating temperature                     -20℃ to+55℃(-4F to 131°F)
Storage temperature-35°℃ to+75°℃ (-22°F to 158F)
Mounting/DIN railDIN rail EN/EC 60715
Protection degreeIP40 for front panel/IP20 terminals
Operating position                                    any
Overvoltage cathegory                                  III.


Overcurrent relays are electrical protection devices that are designed to open or trip a circuit when the current flowing through it exceeds a certain level, but on the higher side. There are several different types of overcurrent relays, each of which is suited for a specific application. Electricians should, therefore, be familiar with these relays and their applications when selecting the type to use.

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I am William, Electrical Engineering Author. Dedicated to writing technical articles on Timer Relay, Monitoring Relay, Surge Protection Device and other electrical devices. With 7 years of writing experience, I am committed to providing accurate and in-depth expertise to my readers.


    I have a 100 hp motor that keeps stalling in a log cut and causing a locked rotor condition burning up the fuses what would i have to buy to stop us from burning so many 200 amp fuses. Shutting down the motor by dropping out the starter.

      We have received your message and our product specialist will contact you as soon as possible. Thank you for contacting GEYA.Have a good day😀

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