Types of Relays Explained

Puzzled by the seemingly endless types of relays roaming around?

Well you’re in luck as we decided to take a look into 5 common relay types in order to simplify this seemingly daunting topic. 

Basically, many people see a relay as a switch. The main difference between a relay and a switch  is that a switch is operated mechanically while a relay is operated electrically. Although this is a pretty general description, each relay follows this same basic principle. Where things start to differ is with the smaller details between each type of relay. Read on to decode the purposes of these relays and figure out which one is right for you!

Confused on what’s in a relay? Check out Del City’s blog post to get some in depth information on the technical aspects of these products! 

Change-Over Relays 


A Change- Over relay is the most common type of relay. These have 5 pins and a body with two contacts connected to a common terminal. These are wired to be either Normally Open (NO) or Normally Closed (NC.) Confused on the difference between Normally Open and Normally Closed? No worries!

When a relay is NO, it means that it will not conduct electricity until the coil is energized or turned “on.” Basically, the circuit is disconnected when the relay is inactive. On the opposite side, a NC relay will conduct electricity until the coil is energized or “closed.” This means that the circuit is still connected when the relay is inactive.

The Change-Over relay can control two different circuits, one NO and one NC. As the name suggests, it can also switch between these two types depending on your specific needs. No matter what type of circuit (NO, NC, or both), a change-over relay can switch current from one component to another. It is important to note that even though a Change-Over relay can switch between the NO and NC circuits, both cannot be on at the same time.

Time Delay Relay

A time delay relay matches the general outline of a normal relay (as described above), but is not instantaneous. A Time Delay relay can hold a power supply anywhere from 2 seconds to about 3 minutes once power is removed. These Time- Delay relay contacts must either be Normally Open or Normally Closed (see Change-Over relays for a refresher on these terms), as well as a specification on how the delay operates. This may sound complicated, but in reality, it is basically asking if the delay is an “on-delay” or an “off-delay.


Knowing the importance of the delay specification described above is crucial for fully understanding Time Delay relays. An “on-delay” timer starts immediately when the voltage is applied. Once the selected delay time is complete, the contacts will close. These contacts will then stay closed until the beginning voltage is not going to the coil.

On the opposite side, an “off-delay” timer does not start when voltage is applied. One needs to open the control input before the timing actually begins and the contacts will remain closed during this time. Once this time is complete, the contacts will open and the relay will shut off.

Latching Relay


A Latching relay works electrically like a normal relay, though it maintains its position even after power has been removed. This means that it will stay in either the “rest” or “set” position until the next input of power. This allows it to have a basic memory attribute. 

An example of a latching relay would be when multiple light switches control a single light. The relay will need to remember what position it was in, so that it can properly turn the light on or off. If the relay had not “latched”, the light switch would not be in the correct position to change the light’s status.

Solid State Relay


A Solid State Relay is set apart by one main thing: no moving parts. With other types of relays, the contacts moved in order to transfer the current from one terminal to the next. This is not the case with a Solid State Relay. This allows the relay to be faster than other relays as well as likely have less wear and tear throughout time.

Because the parts are not moving while the relay is in action, it can be considered very durable in comparison to other relay types. It can be activated many times without fail as opposed to the other types of relays we have discussed, which have shorter life spans. A Solid State relay is also equipped with ignition protection. When does this come in handy? This relay can survive in explosive environments and are much less sensitive to other external factors. 

Potted Relay

A Potted Relay is pretty simple once you understand the other types of relays. What sets this one apart is the added protection. When a relay is potted, it means that it was sealed with some substance in order to act as a barrier against harsh conditions or other possible obstacles. This also allows it to be more resistant to shock or vibrations. Common sealants for potted relays are thermosetting plastics and silicone rubber gels, among others. This is definitely the kind of relay you are looking for if your project is set in a more intense environment. 

Hi-Amp Relays are also used in a variety of applications and can be found in many of the designs mentioned above. These are meant for higher power jobs where you need a bit more “oomph” in your relay. Del City is proud to have expanded our line with Bosch-Tyco Hi Amp Relays commonly used for engine control, glow plug, heated screens, preheating systems, and more!

After seeing these types of relays, hopefully your woes have been put to rest! Confused on how a relay works? Want to read more about types of automotive relays? Check out one of our other articles exploring this topic!

If you still have questions, don’t hesitate to reach out to our Technical Support at 1.800.654.4757!

Posted in Relays & Power Distribution.