Every UL924 Relay Other Than ESRN

Tech Tuesday UL924 Relay

It’s midnight on a cold and quiet night. The wife and kids are out of town while you’re at home reviewing wiring diagrams. You hear the distinct sound of your fridge door closing. You carefully walk downstairs. No one is there. You go back to reviewing the relays that have been specified into this building. Footsteps. You turn around. No one is there. No one behind the curtain, no one under the bed, no one anywhere. Frightened, you do the only thing that gives you peace in this world – you go back to providing quality products for your customers. You sit down at your desk. Your eyes gaze toward the emergency lighting section. You pull out your pen and begin to draw a relay.

Just as you draw the final line, a hand grabs your wiring diagram! The shadowy figure dashes out the window before you get a good look at him. Left wondering who it could have been, you notice a piece of paper left where you spent hours slaving over your, now ruined, project. “You didn’t use a UL924 relay – The UL Inspector.” Attached was a bill for their time.



The ESRN is Functional Device’s most popular UL924 relay. It has automatic load control, which allows you to control the lights on your emergency circuit with the same wall switch and dimming signal as your normal circuit. It has many quality-of-life features for passing inspections, such as test buttons and indicator lights. If you were looking for a single UL924 device that can do everything, the ESRN is a great choice.

UL924 Relay Limited Use Cases

However, all those extra features do come at a cost. The lawyers are telling me to say a small cost, but an additional cost, nonetheless. If all you’re looking for is something to meet the “UL924” requirement, take a minute to check out our other product offerings. All these products are able to bring lights to full brightness in an emergency situation.

  • ESRN-1 Perfect if you want all the quality-of-life features of the ESRN but the lighting application does not require dimming override
  • ESR2401B If all you’re looking to do is shunt around the wall switch OR dimming signal when normal utility power is lost
  • ESR01P A double pole relay perfect for shunting around 3-wire dimming in the event of loss of normal utility power
  • ESRBE277C If you have separate circuits of emergency and normal lighting but during normal operation you want to turn them on and off with a single switch

These are just some of Functional Device’s UL924 products. If the voltages aren’t quite right or you want a different housing size, be sure to check out our full listing.

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Noah Smith
Noah Smith

Noah Smith, or as his friends call him "Noah", is a design engineer at Functional Devices. He graduated from Indiana University in 2018. Just kidding, he graduated from the superior Purdue University with a Bachelors degree in Electrical Engineering in 2018.

Outside of work, Noah spends his time fantasizing about going back to work. He is a seasoned traveler, having visited almost two states. His weekends are spent with his wife and what has been described as "too many cats."

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