Monitoring Relays

Monitoring relays help to protect some of the most expensive and sensitive equipment in industry. They are also used to provide protection for the components in some appliances. These devices prevent machinery and electronics that are sensitive to fluctuations in the power grid by reacting to specific types of changes. Relay technology itself is not new. Relay switches have been in use for over 100 years and are basic components of electrical systems and basic tools of electrical design and engineering.

Relay switches have become much more advanced over the decades, however. This allows them to be set to very specific tolerances and, therefore, to provide excellent protection for the devices that they are used to monitor.

The Basics

Certain types of electrical equipment are very sensitive to fluctuations in the power supply that provides them with energy. For example, a phase imbalance of a couple of percent can overheat electrical motors and other devices, potentially destroying very expensive equipment. Changes in current, temperature and other variables can result in the complete loss of a piece of machinery and, along with it, the entire investment that the company made in the machinery. This is why it’s vital to make sure that devices have some level of protection that is automatic, reliable and precise.

Relays are used to protect against the following variances in the electrical supply:

  • Current fluctuations
  • Phase variances and reversals
  • Heat fluctuations
  • Voltage fluctuations
  • Frequency fluctuations

Modern power supply systems are very reliable but there are still plenty of instances where a variance is introduced into the system that is potentially damaging to machinery. This makes relays necessary equipment for most precision machinery. Aside from the hazards presented by the electrical supply provided to the machine, the machine itself can present a hazard if it has a malfunction and the load suddenly increases or decreases or other problems manifest. Relays protect the machine and the circuit from both sides and help to prevent the loss of valuable equipment.


Monitoring relays can be used in any application where a change in voltage, current, phase or another factor is a threat or where it provides valuable feedback. For instance, relays are used in alarm systems where a change in voltage indicates that a door or window has been opened or broken. The most advanced monitoring relays are usually found on factory floors, however,

Some of these relays are adjustable. They can be used to monitor different variables and to react in different ways when specific tolerances are exceeded. For example, immediately shutting down a machine may be more dangerous to the device than letting the voltage get over or under norms by a certain amounts, so the relay can be set to react only if it reaches a threshold that is well outside of tolerances. This ensures that conditions that are less than optimal, but hardly catastrophic, don’t result in an automatic and potentially catastrophic shutdown of a machine.

Monitoring relays can be used to protect electronic and mechanical equipment with equally good results.

The following industries are only a few that make use of these devices in various capacities:

  • Security
  • Commercial Kitchens
  • Manufacturing Plants
  • Electrical Stations
  • Elevators and Escalators
  • Pumping Stations

There are many more. The technology that has been developed in the last 20 years has made relays even more sensitive and flexible than they have been in the past. This has made industry more efficient and helps to ensure that the highest safety standards can be maintained in factories, power plants and other locations around the world.

Voltage Sensitive Relays

Voltage-sensitive relays, just as the name implies, use voltage as the variable that triggers the energizing or de-energizing of a circuit. An example of these relays and their functions can be founding maritime applications. A voltage sensitive relay is frequently seen in maritime battery charging systems.

Most ships use two batteries. One powers the engines during startup and the other is used to power the ship’s electrical equipment. A ship’s engine starting equipment needs a strong spike of electricity while the electronic equipment needs to be insulated from these spikes. The voltage sensitive relay detects the voltage being put out by each battery. It will allow both of them to be charged at once under certain conditions but, when the voltage changes, it can disengage and separate the batteries. This prevents the electronic equipment from being spiked by the starter battery and prevents the electronic battery from being drained by the starter.

Phase Sensitive Relays

Phase sensitivity prevents sensitive equipment from being damaged by phase imbalances or reversals. These relays are oftentimes found protecting electrical equipment—such as motors, compressors and pumps—that need to operate within certain limits or risk being burned out completely.

Electrical power is delivered from the power generation facility in three phases. These phases are offset from one another by 120 degrees and this arrangement ensures that there is a consistent delivery of voltage. A change in the load on a circuit and events such as lightning strikes can interrupt this phase. In some cases, it can reverse the phase.

Phase sensitive relays react to these changes in phase. They can be set up so that a certain phase variance shuts down the circuit, protecting the equipment on the circuit from being destroyed. Phase sensitive relays are adjustable, in some cases, allowing for a wider variety of applications.

Current Sensitive Relays

Electrical motors and other devices can be damaged by getting too much current. Current sensitive relays react when the amperes go over or under a given threshold. Current can increase or decrease and present a danger in many different situations.

When a motor suffers some sort of mechanical failure—broken belt, etc.—it can cause increases or decreases in current. This variance in current can blow out expensive components or lead to a catastrophic failure of the entire device. Relays provide a level of protection that ensures that the devices aren’t damaged because of the surges in current or because of significant drops in current.

Frequency Sensitive Relays

Frequency sensitivity is another way that relay switches can be used to energize or de-energize a circuit. These devices are sometimes variable, sometimes not. They can be set up so that they will energize a circuit when it goes below 50Hz or above 70Hz, for example. Any frequency can be selected on some models. This provides another way that these devices can help to protect electronic equipment. Equipment that is sensitive to frequency changes will simply be shut down if the circuit goes into an over- or under-frequency state.

Temperature Sensitive Relays

Temperature is another variable that can be used to provide input that triggers a relay to energize or de-energize a circuit. These devices have to be manufactured so that they’re precise enough to prevent tripping in conditions that aren’t appropriate and that may end up disrupting workflow.

Temperature-sensitive relays can be manufactured so that they are resistant to tripping in the event of changes in air temperature and other variables that are unrelated to the state of the circuit that they’re monitoring.

Time Delay

Time delay features allow a relay to be delayed in coming online or in tripping in the event of a situation that causes them to de-energize the circuit. This can be used to allow for proper shut down of machines and to prevent nuisance tripping from conditions that aren’t related to the circuit itself. Relays with time delay features have widespread applications in security systems, where they allow the user to vacate the premises being monitored before the relay is engaged and the alarm circuit is energized.



ABB is a manufacturer of industrial power technologies and automation technologies. It is a global company that has offices in over 100 nations around the world. The company has an extensive website where their various products are listed and described. The company is involved in creating sustainable technologies, in addition to its many other enterprises.

Broyce Control

In business since 1962, Broyce Control is a UK-based enterprise that produces a variety of relays. The company produces time delay relays, earth leakage relays and numerous other products. They offer a 3-year guarantee on some of their products and are an ISO 9001 registered firm.


Crouzet manufactures a variety of automation control products. The company has been in business for over 80 years. They make custom products for manufacturers and are among the companies that have started to incorporate ecologically-friendly designs into their components. They have been recognized with several awards for the quality of their products.


There are few companies as associated with industry as is Siemens. They have been in business for over 160 years, making them one of the oldest companies in technology and it is the largest electrical engineering company in Europe. They have interest in healthcare, energy and many other fields. Their products are known worldwide and the company has an excellent reputation for quality.


Omron is a Japanese company that was launched in 1933. Omron manufactures a variety of different products but has a particularly developed presence in the medical industry. The company also manufactures parts for very large machine applications, such as oil rig controls. The company was among the first to develop the ATMs that you see all over the urban landscape today.


Telemecanique is no more. The company is now owned by Schneider Electric, though that company does offer the entire Telemecanique catalog of products. The company dates back to the 1800s, is based in France and is now a global entity and a leader in the manufacture of industrial electrical components


Tempatron is located in the UK and does business worldwide. The company dates to 1968 and manufactures timers, sensors and other control products. The company has a very diverse catalog and maintains a website where it is available to users. They are an ISO 9001 company.


Dold is a family-owned company that manufactures a variety of industrial control products. They manufacture relays, switches and much more. The company is among the leaders of Europe’s ISO 9001 relay manufacturers. The manufacturing plant is located in Germany and has been in business for over 80 years.


TELE is an Austrian company that has been in business for approximately 50 years. The company manufactures industrial control components, including relays, and has expanded its reach into the UK. The company produces components that are designed to be environmentally-friendly and has over 50 trading partners worldwide.

Schneider Electric

The parent company to Telemachanique, this French firm is among the world’s leading manufacturers of industrial control components. The history of the company dates back to the 1800s. Their products include an enormous range of electrical engineering components.


RS manufactures a huge variety of electrical components. The company manufactures a variety of industrial control products, including relays, fuses, circuit breakers and more. They are based in the UK and have an extensive online catalog of what they offer to clients.

Phoenix Contact

Phoenix Contact is a worldwide manufacturer of electrical components. The company has a workforce of over 11,000 in total. Their products include protection systems, automation components and much more. They have been in business for over 80 years.

Merlin Gerin

Is another electronics manufacturer that has been folded into the Schneider Electric brand. All of their products have been rebranded with the Schneider Electric design and packaging. Their products include industrial control components, including relays.

HOYT Electrical Instrument

HOYT Electrical Instrument was founded over 100 years ago. The company manufactures a variety of components out of a 30,000 square foot manufacturing plant located in New Hampshire. The company produces relays, shunts, transformers and a huge list of other components. They have a good reputation for quality and an extensive client list.

Carlo Gavazzi

Carlo Gavazzi is still headed by the man from whom the company takes its name. The company is a US-based manufacturer of electrical control products, including relays. They are situated in IL. The company does business across North America and the world and works with a variety of industries, including security, commercial kitchens and many more.

Leave a comment

Your email address will not be published. Required fields are marked *