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What is Voltage Monitoring Relay and What Does it Do?

Voltage monitoring relays
Voltage monitoring relays
Relays: https://www.designnews.com

A voltage monitoring relay is designed to monitor voltages and provide a safe shutdown of equipment in the event of a voltage abnormality. Below, we take a detailed look at what it is, its function in a power system, and other key things to know about this type of monitoring relay.

What is Voltage Monitoring Relay?

A voltage monitoring relay is simply a voltage protection device that will de-energize equipment when voltage changes occur outside of safe levels. Its main purpose is to protect against voltage abnormalities rather than regulate voltage.

The typical voltage monitoring relay contains the tripping mechanism, which is often an electromagnetic coil, a control circuit with adjusting features, and the contact mechanism.

The contacts will typically close when the voltage is within the normal range and open when an abnormal voltage is detected.

Voltage relays are designed to protect both ac and dc voltages. They can also protect a single phase or a three-phase system depending on the specific needs of the application. Here is more about the relays for different phase systems.

Single Phase Voltage Monitoring Relay

A single-phase voltage monitoring relay is designed to protect against voltage abnormalities in a single-phase system. This type of voltage monitoring relay is typically used in residential applications, where current and voltages are low.

The single phase voltage protection relay may also be used in commercial settings. Usually, it detects voltages that are on the higher or lower side of what’s safe for the system and its equipment.

Three-Phase Voltage Monitoring Relay

A three-phase voltage monitoring relay is built for use with three-phase networks. Applications of the 3-phase voltage monitoring relay include industrial settings, data centers, and other commercial applications that involve high voltage networks.

Unlike the single phase type, the 3-phase voltage monitoring relay will also usually monitor other parameters such as phase sequence, phase loss, and asymmetry. It’s, as a result, also called a phase sensing relay.

The voltage monitoring relay function in a power system
The voltage monitoring relay function in a power system
Resource: https://www.youtube.com/watch?v=_hctM7G-PUw

Voltage Monitoring Relay Function

Voltage monitoring relays are typically used in conjunction with other types of protection devices, such as circuit breakers, RCDs and fuses. Together, these devices form a comprehensive protection system for electrical equipment.

The main voltage monitoring relay function is to monitor the voltage and provide a safe shutdown of equipment when necessary. Usually, the relay will offer protection for under voltage, overvoltage, or both.

There are also voltage monitoring relays that offer protection against voltages outside a specified band or window. The different VMR relay types are explained below.

Under and Overvoltage Protection Relay

The voltage monitoring relay will detect (and react) to both either an undervoltage or overvoltage condition. Under voltage is defined as a voltage that falls below the predetermined safe level while overvoltage is defined as a voltage that exceeds the safe level.

The specific voltages that will trigger the relay depend on the needs of the application. For example, in some applications, a small voltage drop may not be cause for concern while in other applications; even a small voltage drop can damage equipment.

Voltage Band Relay Protection

In some cases, it may be necessary to protect against both undervoltage and overvoltage conditions. This is where a voltage band relay comes in. A type of monitoring relay is designed to protect equipment from both types of conditions by shutting down the equipment when the voltage goes outside of the safe range.

Voltage band relays are typically used in critical applications where equipment must be protected from both types of voltage conditions or where the voltage must not go outside of a specified range.

Voltage monitoring relay for motor protection
Voltage monitoring relay for motor protection
Resource: https://www.youtube.com/watch?v=7sf7XNiP0B8

Voltage Monitoring Relay Applications

Monitoring relays for voltage protection are used in many different applications where it is critical to maintain voltage within safe limits. Some of the most common applications for voltage monitoring relays include:

  • Motor control centers
  • Pump control panels
  • Generators
  • HVAC systems
  • Lighting systems
  • Solar power installations
  • Wind power generation plants
  • UPS systems
  • Telecommunications equipment
  • Electrical distribution panels
  • Transport

One of the main advantages of using a voltage monitoring or voltage protection relay is that it can provide protection without the need for human intervention. This can be critical in applications where there is a risk of electrical shock or fire.

Another advantage of voltage monitoring devices is that they can be used to protect against a wide range of voltage changes. This includes momentary fluctuations as well as sustained changes in voltage.

Different designs of the voltage monitoring relay
Different designs of the voltage monitoring relay
Resource: https://www.youtube.com/watch?v=NJvBXzfjfqE

Voltage Monitoring Relay Price

The price of a voltage monitoring relay will usually vary depending on the specific features and design of the device. Some of the factors that can affect the price include:

  • The type of protection offered (Undervoltage, overvoltage, or both)
  • The voltage range that the device can protect against
  • The specific applications for which the device is designed
  • The number of poles (one, two, or three)
  • Whether the device is designed for use with AC or DC voltage
  • The manufacturer of the device

Generally, voltage monitoring relays are not expensive devices. For example, a basic single-phase udervoltage monitoring relay can cost as little as $20 while a more sophisticated voltage band relay can cost around $100.

As with any electrical device, it is important to choose a reputable manufacturer when selecting a voltage monitoring relay. This will ensure that the device meets the required protection and safety standards and that it is covered by a decent warranty in case of any problems.

To get a more accurate idea of the voltage monitoring relay price, it is best to consult with a supplier or manufacturer. Many manufacturers will offer discounts for larger orders.


A voltage monitoring relay plays a critical role in protecting equipment from voltage abnormalities. These relays can provide protection against a wide range of voltage changes and are often used in applications where it is critical to maintain voltage within safe limits.

When selecting a voltage monitoring relay, it is important to consider the specific requirements of the application and the type of equipment to be protected. Additionally, the environment in which the relay will be used should also be taken into account.


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.



    Schakelt bijvoorbeeld een overspanningsbewalingsrelais automatisch weer in (herstelt de stroomkring) zodra de spannng onder het ingestelde niveau komt? Ik zou een zonnestroominstallatie zo willen beveiligen (althans de omvormer) tegen kortsluitspanning die soms bij koude hoog kan oplopen. Ik lees soms dat de stroom weer ingeschakelt wordt na een aantal seconden maar in mijn geval zou dat urenlang in en uitschakelen betekenen.

      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😀

    7ncanta leer cosas de lo hoy en día uno se sorprende

    Perfect! A voltage relay is a combination of an electronic voltage monitoring device and a power section of a load disconnector. Its purpose is to disconnect the load if it goes beyond the set limits in case of accidents in the electrical network.

    Bonjour je voudrai un petie renseignement sur les relais voila je possede une pompe de bassin de 65w que j’alimente en 220v mais je suis pasé par des paneaux solaire et un onduleur qui fourni 220v pure sinus cela fonctione tres bien mais quand ma batterie et la nuit arrive ma tension baisse est me onduleur ce met en defaut je donc obligé de débrancher ma prise de l’onduleur et de rpasser par le secteur j’ai fait un essaie avec 2 relais un no et un nc cela fonctione mais je ne coupe pas l’onduleur comment puis je proceder pour couper l’onduleur merci a vous

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