Transcript:
[0m:00s] Hey, I’m Mitchell. Welcome to another video in the RSP education series. Have you ever wondered why some relays have one switch while others have two or even four, or why solid state relays, SSRs, are taking over in industrial automation? Today we’re going to dive deep into relay contact configurations like single pole single throw, single pole double throw, double pole double throw, and then explore solid state relays. Stick around because by the end you’ll know exactly which relay to use for your next project. If you like this kind of content and want more educational videos, like and subscribe. This video is for educational purposes. Consult a professional for your application. RSP Supply is not liable for any misuse of this information. Jump in with me.
[0m:53s] Let’s start simple with single pole single throw. A single pole single throw relay controls one circuit and has one switching position. When energized it closes the circuit on, and when deenergized it opens off. Think of it like a basic light switch. Click on, click off. Then we move to single pole double throw. This relay has three terminals, common, normally open, and normally closed. When powered the common switches from normally closed to normally open. It can only touch one contact at a time and is perfect for toggling between two circuits. Double pole double throw means two separate circuits with two switching positions per circuit. It’s like having two single pole double throw relays in one package and is commonly used to reverse a motor’s polarity.
[2m:12s] Now let’s talk about contact load ratings. This is critical because ignoring these can damage your relay. Current rating tells you how many amps it can handle continuously. Voltage rating matters because higher voltage creates larger arcs. Inrush current is important because motors and solenoids can spike up to ten times their normal current. Contact material also matters, with silver alloys used for high power and gold used for signal level switching.
[2m:44s] Now let’s clarify the difference between relay terminals and contacts. Terminals are the external connection points, the physical pins you wire into your circuit. These connect to the internal contacts such as common, normally open, and normally closed, as well as the coil terminals. Contacts are the internal switching elements that physically make or break connections and define the relay type. Every relay has coil terminals and contact terminals. Coil terminals are typically labeled A1 and A2 and power the relay coil to generate a magnetic field. These require a small amount of power, such as 24 volts or 10 to 50 milliamps.
[4m:00s] Contact terminals such as 30, 87, and 87A carry the switched current on the load side of the relay. Terminal 30 is typically the power input, while 87 and 87A are the switched outputs through normally open or normally closed contacts. To recap, coil terminals like A1 and A2 act as the trigger, while contact terminals handle the actual power switching. That’s the full breakdown of relay contact types, from single pole single throw to double pole double throw and solid state relays. Always check contact ratings, understand your load requirements, and when in doubt choose solid state for long lasting silent switching. For a full line of relays and hundreds of thousands of industrial automation products, visit rspsupply.com.