Transcript:
[0m:06s] Hey, it’s Mitchell. Welcome to another video in the RSP Education Series. What’s that tiny switch that controls massive machines? It’s relay coil actuation. Miss this and your whole automation setup could fail. Stick around, because in the next 60 seconds you’ll never wire a relay wrong again. 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. With that said, let’s jump into it.
[0m:41s] Coil actuation is what makes a relay work. The coil acts as an electromagnet. When power is applied, it creates a magnetic field that pulls the relay’s internal switch, or contacts, into position. When power is removed, a spring returns the contacts to their normal state. Here are the key specs you need to know. First, voltage rating—match your relay to the power supply, whether it’s 12V, 24V DC, or 120V AC. Next, current draw—typically between 5 and 150 milliamps, meaning relays use very little power. AC versus DC is another factor. AC coils tend to hum slightly, while DC coils are silent. Reverse polarity only matters for DC coils; if wired backward, they simply won’t actuate. It’s like putting batteries into a remote the wrong way—it won’t work, but it won’t break either. Flip the wires and you’re good.
[2m:01s] If you hear no click when the coil should activate, you may have a bad coil. Now let’s talk about contacts, because these are what actually control the circuit. Every relay has three main contact types. First is NO, or normally open. Think of it like a drawbridge—it’s open by default, preventing current flow. When you power the coil, the bridge lowers, closing the circuit and allowing current to pass.
[2m:35s] Next is NC, or normally closed. It’s the opposite—a door that stays closed until you power the coil. Once the coil energizes, that door swings open, breaking the circuit. Finally, there’s COM, the common terminal. It acts like the pivot of a seesaw, switching connection between the normally open and normally closed terminals depending on coil state.
[3m:02s] Quick recap: NO means open until you power the coil, NC means closed until you power the coil, and COM is the common connection that switches between them. Mixing up NO and NC can cause big problems—like turning a system off when you meant to turn it on. Lock it in. The coil is an electromagnet—power it and it pulls the contacts. Wrong voltage or reversed DC polarity means no click. NO starts open, NC starts closed, and COM is the switcher. Get it right and your relay system runs smoothly. 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 automation.