# What Is a Relay? How It Works, Types and Selection | Navea A relay uses an electrical control signal to open or close another circuit. See how relays work, the main relay types and how to choose the right one. --- # What Is a Relay? Operating Principle, Relay Types and Choosing the Right One 26 October 2026 · Navea Electronics ![A transparent electromechanical relay and a PCB power relay representing relay types](https://naveaelectronics.com/assets/rehber/role-nedir-kapak.jpg) - What does a relay do? - How does a relay work? - 12 V, 24 V and 230 V relays - Types of relays - Electromechanical relay vs SSR - How to choose the right relay? - Relay sockets - Relpol and TE SCHRACK - Frequently asked questions A relay is a switching device that uses an electrical control signal to open or close another circuit, or to change its connection state. In electromechanical relays this is done with a coil and moving contacts; in solid state relays it is done with semiconductors. Relays are used in automation panels, electronic boards, machinery and control systems. Choosing the right relay is not done by looking at the voltage or current value alone. Control voltage, the characteristics of the load to be switched, contact arrangement, operating frequency and mounting type should be evaluated together. Two relays of the same size or with the same number of pins can have different electrical characteristics. ## What does a relay do? The basic function of a relay is to open, close or change the electrical connection in the load circuit in response to a control signal. With a suitable relay, a load at a different voltage or power level can be managed using a low-power control signal. Depending on the application, relays perform the following functions: - **Load switching:** Switches on a lamp, heater, valve or another control element. - **Isolation between circuits:** In products with suitable insulation properties, provides galvanic isolation between the control and load circuits. - **Contact multiplication:** Changes the state of more than one contact set with a single control signal. - **Interfacing:** Helps establish a connection between a controller output and field equipment. For example, a PLC output can drive the coil of a suitable interface relay, which in turn controls a valve or a contactor coil. In this case, the PLC output must be able to drive the relay and the relay contacts must also be suitable for the connected load. ## How does a relay work? In an electromagnetic relay, a magnetic field is created when a suitable voltage is applied to the coil. This field attracts the moving armature and changes the position of the contacts. In a standard monostable relay, when the coil is de-energised, a spring mechanism returns the contacts to their initial position. Bistable, or latching, relays work differently: depending on the product design, the contact position can be maintained until a new control command is given. ### Main parts of a relay - Part - Function - Coil - Converts electrical energy into a magnetic field. - Magnetic core and armature - Allow the magnetic force to move the contact mechanism. - Contacts - Open, close or change over the load circuit. - Spring mechanism - Returns a monostable relay to its de-energised position. - Housing and terminals - Provide mechanical protection and electrical connection. ### What do COM, NO and NC mean? In standard monostable electromechanical relays, the NO and NC designations indicate the normal state of the contacts while the coil is de-energised; in latching relays the contact state may depend on the last command. - Marking - Meaning - Coil de-energised - COM - Common contact - The common terminal of a changeover contact set. - NO - Normally open contact - The connection is open. - NC - Normally closed contact - The connection is closed. - CO / C/O - Changeover contact - The common terminal switches between NC and NO. For example, 1CO refers to one changeover contact set and 2CO to two changeover contact sets. Which pins the contacts correspond to should be checked in the manufacturer’s wiring diagram. The number of pins alone does not show the connection arrangement. ## What do 12 V, 24 V and 230 V relays mean? In electromechanical relays, an expression such as “24 V relay” usually refers to the **rated coil voltage**. The voltage and current of the load the contacts can switch is a separate characteristic. For example, a relay with a 24 V DC coil can switch an AC load at a different voltage if it has suitable contact ratings. A 24 V coil does not mean that only 24 V can pass through the contacts. However, the following distinctions must be made: - **A 24 V AC coil is not the same as a 24 V DC coil.** - The coil voltage and the switching voltage of the contacts are different. - The coil power consumption must be compatible with the capacity of the output driving the relay. - In products with a diode or LED, connection polarity may matter. The actual voltage at the coil terminals can be affected by supply tolerance and by voltage drops across the cable and driver. Coil resistance and operating behaviour can also vary with temperature. The TE Connectivity coil drive guide explains the importance of correct driving for relay performance. [TE Connectivity coil drive guide](https://www.te.com/en/products/relays-and-contactors/electromechanical-relays/intersection/coil-drive-relay-contactor-performance.html) ## What are the types of relays? Relays are classified by operating technology, mounting type and function. These classes are not alternatives to one another. The same product can be an electromechanical PCB power relay. ### PCB power relays PCB relays are mounted on a printed circuit board. In devices that switch power, the layout on the board, pin spacing and insulation distances matter as much as contact capacity. Relpol RM84 and RM85 are examples of miniature power relay families. The RM85 family offers different coil and contact options; the manufacturer specifies use on PCBs and with suitable sockets. Exact specifications should be checked against the full product code. [Relpol RM85 product family](https://www.relpol.pl/en/Products/PCB-relays-for-electronics/Miniature-PCB-power-relays/Miniature-relays-RM85) ### Industrial plug-in relays Plug-in relays are connected to the system through a suitable relay socket. During maintenance, they can make relay replacement easier by leaving the wiring in the socket. In panel applications, the socket’s connection layout, current capacity, mounting type and retaining accessories should be evaluated together with the relay. ### Interface relays An interface relay is used between the control system and the field circuit. It takes on tasks such as passing a PLC output to another circuit and, under suitable conditions, providing electrical isolation. The term “power relay” emphasises load switching capacity, while “interface relay” emphasises the role in the circuit. The two concepts therefore do not have to be entirely separate product groups. ### Solid state relays A solid state relay, or **SSR**, switches with semiconductor elements instead of moving contacts. It can be considered for applications that require silent operation and frequent switching. When choosing an SSR, the AC/DC type of the load, input voltage, output switching method, off-state leakage current, conduction losses, overcurrent withstand and cooling conditions should be examined. An SSR output being off does not mean that safe electrical isolation is provided on the load side. ### Bistable, timer and monitoring relays Depending on their design, bistable relays can maintain their contact state without continuous coil power. Timer relays perform a specific delay or timing function. Monitoring relays give an output by monitoring voltage, phase or similar parameters. The functions of these products differ. In a project, the task to be performed should be defined first and then the suitable product group selected. ## What is the difference between an electromechanical relay and an SSR? - Feature - Electromechanical relay - Solid state relay - Switching structure - Moving mechanical contact - Semiconductor output - Operating noise - Switching noise may occur. - No mechanical switching noise. - Switching frequency - Limited by mechanical and electrical life. - Suitable products allow frequent switching. - Open circuit behaviour - There is an open contact gap. - Leakage current may flow while the output is off. - Thermal evaluation - Coil and contact heating are examined. - Conduction losses and cooling needs are important. The absence of a moving contact in an SSR does not mean it is more suitable or safer in every application. Before maintenance, the load circuit should be de-energised with a suitable isolating device and the absence of voltage verified. Leakage current while the output is off and heat loss under load can affect the selection. The heat sink requirement should be determined from the product’s technical data. [Solid state relay technical explanations](https://www.ia.omron.com/support/guide/18/further_information.html) ## How to choose the right relay? The right relay must suit both the control circuit and the switched load. The checklist below makes product comparison easier. - Criterion - What to check - Control characteristics - Coil or input voltage, AC/DC type, power consumption - Load characteristics - AC/DC, operating voltage, continuous current and inrush current - Contact arrangement - NO, NC or CO; required number of poles - Load type - Resistive, inductive, capacitive or low-level signal - Operating frequency - Number of switching operations and target electrical life - Mounting - PCB, socket, panel or DIN rail - Environmental conditions - Temperature, vibration, humidity and contamination - Compliance - Relevant approvals, insulation requirements and project specification ### Evaluate contact current together with load type The current value printed on a relay does not mean it has the same switching capacity for every load. A value given for a resistive load should not be applied directly to an inductive load such as a motor or valve. LED drivers and devices with capacitive inputs can also draw high current at the moment of first energisation. Therefore, not only the continuous operating current but also the peak current at switch-on, its duration and the relay’s permitted inrush current withstand should be evaluated. AC and DC switching limits can differ. The selection should be made using the values published for the relevant load and the electrical life curves. [TE Connectivity relay selection and application guide](https://www.te.com/content/dam/te-com/documents/aerospace-defense-and-marine/aerospace/global/hpg/5-1773450-5_Sec5_MidRangeRelays.pdf) ### Distinguish mechanical life from electrical life Mechanical life relates to operating cycles performed without an electrical load on the contacts. Electrical life shows switching endurance under specified load conditions. A high mechanical life value therefore does not show that the relay can perform the same number of full-load switching operations. The expected number of cycles in the application should be compared with the electrical life under suitable load conditions. ## What does a relay socket do? A relay socket is an intermediate connection element through which the relay is connected to the system and can be removed and replaced when necessary. It makes mounting and replacement easier, especially during panel maintenance. When choosing a socket, having the same number of pins is not enough. The following should also be checked: - Relay-socket compatibility specified by the manufacturer - Pin layout and wiring diagram - Current, voltage and temperature limits - Wire cross-section and terminal connection method - Retaining clip and, if any, indicator or protection module The permissible load of the system should be determined by taking into account the most restrictive current, voltage and temperature limits of the relay and socket used together, as well as the manufacturer’s derating curves, if any. ## Relpol and TE Connectivity SCHRACK relays When researching a relay family, brand and series names can be used to narrow down suitable options. Families such as Relpol RM84 and RM85 include different variants by coil, contact arrangement and other characteristics. TE Connectivity’s **SCHRACK** brand also offers PCB and industrial relay solutions. A brand name alone does not define product characteristics; evaluation should be based on the relevant series and full part number. [TE Connectivity SCHRACK relays](https://www.te.com/en/products/brands/schrack.html) You can find information about the relevant portfolio in Navea’s [Relpol](https://naveaelectronics.com/en/markalarimiz/#relpol) and [TE Connectivity](https://naveaelectronics.com/en/markalarimiz/#te) brand sections. ### Why is the full part number needed when ordering? A series name refers to a product family, while the **MPN** is the manufacturer’s specific part number. Products in the same series can differ in coil voltage, contact material, contact arrangement or housing characteristics. Ordering with only “24 V, 8-pin relay” may therefore not be enough. If an existing product is being replaced, the full code on it, the wiring diagram and the application conditions should be shared together. Physical similarity is not enough when choosing an equivalent either. Electrical ratings, pin layout, load endurance and required approvals should be compared. ## Identify the right relay for your project For product evaluation, prepare the control voltage, the AC/DC type of the load, operating current, inrush conditions, contact arrangement and mounting type. If you are looking for an alternative to an existing relay, include its full part number and technical documentation. For plug-in applications, sharing the socket code as well makes the evaluation easier. To discuss relay and accessory options suitable for your project, you can [contact Navea Electronics](https://naveaelectronics.com/en/contact/). ## Frequently asked questions ### What does “röle” mean? “Röle” is the Turkish word for relay. In electrical and electronic applications, it refers to devices that switch another circuit using a control signal. ### What is the difference between a relay and a contactor? Both can switch electrical circuits. Contactors are mostly designed for applications such as frequent switching of motors and power circuits. The selection should be made not only by current magnitude but by load type and utilisation category. ### Can 24 V AC and 24 V DC relays be used interchangeably? Not unless the manufacturer explicitly states suitability. The same voltage value does not mean the coil structure and supply requirements are the same. ### Does a relay clicking show that it is working properly? No. A click can show that the mechanism is moving, but it does not prove that the contacts work correctly under load. Contact wear, contact welding or high contact resistance should be evaluated separately. ### How is a relay tested? In a de-energised and safely isolated circuit, coil and contact checks can be carried out according to the manufacturer’s diagram. A continuity or resistance measurement alone does not verify performance under load; the necessary functional tests should be performed by competent personnel with suitable equipment. ## Related guides - [What Is a Connector?](https://naveaelectronics.com/en/guides/what-is-a-connector/) - [What Is Heat Shrink Tubing?](https://naveaelectronics.com/en/guides/what-is-heat-shrink-tubing/) - [TE Connectivity Distributor in Türkiye](https://naveaelectronics.com/en/brands/te-connectivity/) - [Relpol relays](https://naveaelectronics.com/en/markalarimiz/#relpol) ### Cookie Preferences You can enable or disable each category below. Strictly necessary cookies cannot be switched off; all other cookies run only with your active choice. #### Strictly Necessary Cookies Required for the basic functions and security of the website and to keep your language preference. 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