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What Time Delay Relay Do I Need?

We often get technical support calls asking about Time Delay Relays, but many people are unsure of the type they need:
  • Delay-on-make (DOM) or
  • Delay-on-break (DOB)

Let's look at a simple scenario to better understand the difference between DOM and DOB.

Suppose you have some security floodlights that you want to turn on for 20 minutes when an unsavory character triggers a nearby motion sensor. What would happen if a DOM relay were being used?

With a DOM relay, the motion sensor would have to be triggered for 20 minutes before the lights turned on and would turn off immediately once the trigger is gone. Under this setup, the lights don't turn on and the unsavory character gets away. However, if a DOB relay were being used, the results would be quite different.

With a DOB relay, the motion sensor only needs to be triggered for a brief time before the lights turn on. Once the trigger is gone, the lights will remain on for the 20 minutes, and the unsavory character gets caught.

If you have an application that involves timing take a look at the following products:

As always, if you have any questions or need help selecting the right relay, be sure to contact us.

Confidence and Peace of Mind

Functional Devices, Inc., located in the United States of America, has been designing and manufacturing quality electronic devices since 1969. Our mission is to enhance lives in buildings and beyond. We do so by designing and manufacturing reliable, high-quality products for the building automation industry.  Our suite of product offerings include RIB relays, current sensors, power controls, power supplies, transformers, lighting controls, and more.

We test 100% of our products, which leads to less than 1 out of every 16,000 products experiencing a failure in the field.