What Is a Relay and What Does It Do?

A relay is an electrical switch with the capacity to close and open circuits by utilizing electromagnetism to convert small electrical currents into larger currents. These conversions can be achieved as the electrical inputs activate electromagnets to either make or break existing circuits. Moreover, relays control circuit contacts that are normally open (NO) or normally closed (NC). 

Relays utilize weak inputs to power stronger currents, allowing them to serve as either switches or amplifiers for an electric circuit. Versatile in function, relays are helpful devices in both complex and simple assemblies. More than that, they can be designed to align with specifications needed for certain applications.

Normally used in control panels, relays allow for manufacturing and building automation to control and switch smaller current values in a control circuit. As such, the most common application of relays include switching from high to low currents, or vice versa. For example, HVAC units powered by temperature sensors necessitate high levels of amperage that exceed the capacity of their wiring, and relays can successfully provide the needed amplifications to convert these currents.

In some instances, a single relay has the ability to activate multiple circuits, enabling one input to initiate a number of other effects. They can also work together with other relays to perform a cost-effective form of Boolean logic functions. Additionally, relays have the ability to reduce the need for high-amperage wiring and switches, which can be unfeasible for smaller circuits due to their large size and high costs.

As relays differ in size, capacity, and function, the one factor that defines a myriad of relays is whether they are normally open (NO) or normally closed (NC).

Normally Open Relays

In normally open relays, power makes it way through an input circuit, activating an electromagnet. The resulting magnetic field attracts a contact to join another circuit, allowing current to flow through. As the source of power is removed, a spring pulls the contact away from the second circuit, stopping the flow of electricity and turning off the device.

Normally Closed Relays

Similar to a normally open relay, NC relays feature two circuits and an electromagnet that moves a physical contact between two different positions. What differentiates these two relays relies on the default states being reversed. The electromagnet pulls the contact away from the second circuit when the first circuit is activated. As such, NC relays maintain the larger circuit in an ON position by default.

As there are a variety of relays that one can procure for their operational needs, the next section will cover a few of the most common types. 

Time-Delay Relays

Time-delay relays are typically used in applications that require components to be powered for extended periods of time, or when a component needs to be powered ON or OFF after a delay. Most time-delay relays can be categorized as either on-delay timers or off-delay timers.

On-delay timers have the ability to begin timing when an input is applied, providing power to the second circuit after a set waiting period. They are commonly found in alarms and warning systems, and are utilized to prevent power surges.

Off-delay timers are directed by a trigger after the input is energized. When the trigger is removed, the output is energized and de-energized after the time delay. These relays are especially useful for powering devices at set intervals, including washers, dryers, and amusement park rides.

Automotive Relays

Probably the most popular type, automotive relays allow manufacturers to design them with safety features and advanced electrical conveniences. Some automotive relay applications examples include headlights, windshield wipers, internal lighting, and more.

Sequential Relays

This type of relay can be applied to power a myriad of components in a specific order, and they are often found in applications that require powering multiple systems.


As there are a variety of relays that one can acquire for their operational needs, sourcing relays of the highest caliber and well-suited for your specific applications is important. If you find yourself in need of relays, circuits, NSN components, or electronic parts, rely on Purchasing 3Sixty. Purchasing 3Sixty has an ever-expanding inventory of new, used, obsolete, and hard-to-find parts, all of which have been vetted for quality and authenticity. Kickoff the procurement process today with a competitive quote for your comparisons, and see how Purchasing 3Sixty can serve as your strategic sourcing partner.


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