Things you Must Know about Relays



[0m:4s] Hi I'm Josh Bloom, welcome to another video in the RSP Supply education series. In today's video, we are going to be discussing the top five things you must know about relays. Relays are an essential tool for many common electrical circuits that we use on a daily basis. For more information about how relays work, please see our other videos which we will link in the description below. It is important that we have a good understanding of relays, and why they are so critical, and how they can help us. The things we will talk about today should help you better understand relays and some of the things that we must know when using them. Number one, voltage matters. When using relays, it is very important that we consider the voltage that we are using. This applies to both the coil and the contact side of the relay. Most relays are identified using the voltage the coil is rated for. So, if we have a 12 Volt relay, this typically means that that particular relays coil is rated for 12 Volts DC.
[1m:7s] The contact side of the relay will be rated for an entirely different voltage.
[1m:12s] It is very common for the contact side of the relay to be rated for up to 250 volts AC, but it can commonly switch DC voltage as well.
[1m:23s] It is also important to note that AC and DC coils are different and are not interchangeable. So, when using relays, pay attention to the voltage on both the coil and the contact side of the relay, and make sure that you are supplying the correct amount of voltage to that relay.
[1m:41s] Number two, normally open and normally closed: know the difference. Many relays have a normally open and normally close contact. However, some relays will only
have one or the other. It is important to understand the difference between the two so that the electrical circuit you are controlling functions as you intend it to.
[2m:3s] If you do not fully understand how normally open and normally closed contact function within a relay, please reference our other video in which we cover this in great detail. It is most common to use the normally open contact on a relay. However, most circuits can function using one or the other just depending on how it has been set up. So again, know the difference it can help determine whether an electrical circuit will function as planned or not.
[2m:29s] Number three, a relay is not a contactor. Don't get confused. Although relays and contactors function much in the same way, they are not the same. Contactors are generally used in scenarios where large amounts of voltage and current need to be switched. Whereas with relays, you don't typically switch more than 15 amps and 120 volts.
[2m:52s] Use the right device for the right scenarios and you will avoid any problems. Think of it this way: relays, equal low voltage and contactors equal high voltage. Number four a little power goes a long way. It is important to remember why we use relays in most cases. They allow us to control or switch higher voltage circuits with lower voltage control signals. This allows you to isolate yourself and your more sensitive control equipment from your higher voltage circuits, like maybe a motor, for instance. Relays are a cheap and easy way to remotely turn on and off these types of circuits. When in doubt, use relay to switch higher voltage. And number five, relays can be used both ways. Although it is most common to see relays being used to switch a higher voltage circuit, this is not the only way we can use relays.
[3m:49s] Another very common use for relays is to monitor the status of certain devices such as a motor.
[3m:55s] To do this, you would wire the relay so that the coil will become energized when the motor is actually running.
[4m:3s] By doing this, you can send a low voltage control signal back to your PLC or computer to inform you that the motor is, in fact, running. This is very helpful when we want to be able to monitor our electrical circuits and can be used in many different applications. So, remember, relays can be used in more than one way. So, let's quickly recap. Number one, voltage is important. Pay attention to the voltage ratings of the relay. Number two, normally open versus normally closed. Know the difference. Number three, relays are not contactors. Remember relays, equal low voltage and contactors equal high voltage. Number four, we most commonly use relays to switch higher voltage circuit, which is much safer. And lastly, number five, relays can be used in more than one way.
[4m:56s] For a full line of relays and thousands of other products, please go to our website. For more information or other educational videos, go to, the Internet's top source for industrial hardware. Also, don't forget: like and subscribe.