Transcript:
[0m:00s] Hey, I’m Mitchell. Welcome to another video in the RSP Education Series. Relays are one of the most fundamental components in the industrial automation world. They act like switches, but instead of being flipped manually, they’re controlled electrically. Today we’re breaking down relay symbols, diagrams, and the different types you’ll encounter when reading electrical plans and schematics. If you like this kind of content and want more educational videos, please like and subscribe. This video is for educational purposes only. Consult a professional for your application. RSP Supply is not liable for any misuse of this information. Let’s dive in.
[0m:43s] Relay symbols and diagrams can look a little different depending on the standard used. The two main standards are ANSI/IEC and NEMA. ANSI stands for American National Standards Institute, and IEC stands for International Electrotechnical Commission. These two typically use simple symbols—rectangles and lines. The coil is shown as a rectangle, while the contacts are labeled as normally open (NO) or normally closed (NC).
[1m:22s] NEMA, which stands for National Electrical Manufacturers Association, uses more detailed symbols that sometimes resemble the physical relay. The coil may be drawn as a zigzag or curved line, and the contact symbols may look slightly different. Most modern schematics use ANSI or IEC because they’re simpler, but you’ll still see NEMA in older systems. When reading a relay in a schematic, look for two main parts: the coil and the contacts. The coil symbol represents the electromagnet that activates the relay, while the contact symbols show whether the relay is normally open or normally closed. When current flows through the coil, the magnetic field causes the contacts to switch, just like flipping a switch remotely.
[2m:08s] The most common type of relay is the electromechanical relay, or EMR. These relays operate using a coil and electromagnet. When voltage is applied, the coil generates a magnetic field that pulls a mechanical armature, physically moving the contacts to open or close the circuit. Electromechanical relays have several advantages. They can handle high current—often up to 30 amps or more—and provide strong electrical isolation between the control and load circuits. They’re reliable for high-voltage switching and commonly used in motor starters and industrial machinery. However, they do have some downsides. Mechanical parts wear over time, giving them a limited lifespan. They also switch more slowly, with a typical response time of 5 to 15 milliseconds, and they produce an audible click, which can be noisy in sensitive environments.
[3m:17s] Common applications for EMRs include motor control, HVAC systems, and power distribution panels. They’re a dependable, cost-effective choice for many industrial systems. So, to recap: we covered relay symbols, how to read schematics, the differences between ANSI/IEC and NEMA standards, and the pros and cons of electromechanical relays. Whether it’s starting a motor or automating a production line, relays make it happen. Got questions? Drop them below, and don’t forget to subscribe for more industrial tech breakdowns. Until next time, keep those circuits energized. For a full line of relays and hundreds of thousands of other industrial automation products, visit rspsupply.com, the internet’s top source for industrial hardware.