Which Relays Work Best for Certain Applications

Your home depends on you to turn the switches that power its devices and electrical systems on and off. However, commercial buildings must depend on relays, efficient switching devices integral to building automation systems.. 

These “master switches” fill many purposes, including safeguarding electrical components, improving the reliability and longevity of a building’s systems, amplifying currents, and allowing for higher load capacity and remote management.

But there’s no “one size fits all” approach to relays. There are different types for different applications. Let’s explore the unique features of each one and outline when their use might be advantageous.

At Functional Devices, relays are our bread and butter. We offer various options for building automation and lighting controls, including our handy “Relay in a Box®.” While diving into relay types here, we can’t outline all the nuances between relays in one post. Call us to ask your questions and determine which makes sense for your specific needs!

Types of Relays and Their Applications

There are many ways to categorize relays. When we talk about types in this post, we mean the three main classifications based on operation principles. Each design type suits different needs and applications, and understanding each type’s characteristics can help you make the right choice.

When choosing a relay, let its characteristics guide your decision, but remember to consider other factors, such as load requirements, contact configuration, voltage, switching speed and frequency, and environmental conditions.

Here are the three most commonly used relays based on operation principles.

Electromechanical Relays

The grandfather of all relays, electromechanical relays (EMRs), are electrically operated switches that use electromagnets to mechanically switch contacts. Robust and capable of handling a wide variety of voltages and currents, EMRs are most often used in high-power situations. An EMR’s ability to operate high-power circuits with low-power signals is where it shines. 

Advantages of an EMR include:

• Simple design
• Affordable
• Versatile
• Good thermal management (doesn’t produce a lot of heat)
• Reliable for general use

Appropriate applications for EMRs could include:

Of course, an EMR won’t work for every application. Here are some of the characteristics that might limit their use:

• Mechanical wear over time that requires regular maintenance
• Possible mechanical failures and contact erosion
• Larger and heavier design
• Slower switching than other types
• Audible clicking noises when switching
• Require constant power to maintain coil activation
• Can’t perform complex logic or communication tasks

With their cost-effectiveness and ability to manage high loads, EMRs make sense in many basic applications. 

Solid-State Relays

A newer technology than EMRs, solid-state relays (SSRs) have no moving parts and rely on semiconductors for completing electronic switching. They perform well in conditions that require precision, quick switching, and quiet operation.

Advantages of an SSR include: 

• Almost silent operation
• Fast switching speeds
• Longevity
• Durable and reliable with no mechanical parts
• Low power consumption
• Small and compact size
• Efficiency
• Precision
• Low maintenance (possible cost savings in the long run)

Appropriate applications for SSRs could include:

Here are some characteristics of SSRs that might limit their use:

• More expensive upfront than other types
• Generate heat when switching large loads, which can require additional cooling systems or heat sinks
• Limited current capacity
• May require a minimum load to operate (not suitable for small output signals)
• Only a single contact

As you can see, there are many places where EMRs and SSRs can overlap in their applications. Choosing one over the other might depend on desired switching speeds, operational noise, budget, load requirements, etc. As the newer, quieter, and faster technology, SSRs are slowly replacing EMRs in many industries.

Reed Relays

The last type of relay we want to cover is technically an EMR, relying on an electromagnet to mechanically switch circuits on or off; however, a reed relay’s unique, compact construction deserves some focus. The mechanism at play is the reed switch, consisting of two metal ferromagnetic blades hermetically enclosed in a glass tube that touch/switch when enough of a magnetic field is applied.

Advantages of a reed relay include:

• Small and lightweight design
• Fast switching speeds
• Low power consumption
• Longevity
• Protected from the environment by hermetical seal
• Low contact resistance
• High insulation resistance
• Resistant to shock and vibration
• Highly reliable for low-power switching

Appropriate applications for reed relays could include:

With their small size and ability to detect extremely low voltages, reed relays aren’t as interchangeable as EMRs and SSRs are with each other. Reed relays were developed in the 1930s and, despite being an older technology still find a home in many industries, especially where reliable, quick switching of low-power devices is required. 

Functional Devices Takes Charge on Relays

EMRs, SSRs, and reed relays all have advantages and disadvantages. You can ensure optimal performance, safety, and efficiency by aligning the relay’s features with the application's specific demands. 

Functional Devices is here to guide you through how our industry characterizes relays (like resistive ratings, contact types, tungsten ratings, and more!). Besides helping you navigate these differences, we offer a full line of the traditional and widely applicable EMR technology in our “Relay in a Box®” and a select line of SSRs for specific use cases. Our engineers are happy to chat about which one would work best for you! Contact us to explore more.

About Functional Devices, Inc.

Functional Devices, Inc., located in the United States of America, has been designing and manufacturing quality electronic devices since 1969. Our mission is to enhance lives in buildings and beyond. We do so by designing and manufacturing reliable, high-quality products for the building automation industry.  Our suite of product offerings include RIB relays, current sensors, power controls, power supplies, transformers, lighting controls, and more.

We test 100% of our products, which leads to less than 1 out of every 16,000 products experiencing a failure in the field.

Simply put, we provide users of our various products confidence and peace of mind in every box.