Lighting Applications: UL 924 vs. UL 1008

March 24, 2020
Tech Tuesday

While taking tech calls here in Indiana, one thing I often hear about is the confusion between UL 924 and UL 1008 applications. It’s understandable seeing as they both deal with emergency lighting and their construction is very similar, but using one in place of the other won’t sit well with the inspector when they drop by. There are some very crucial differences between the two that we will explore in this blog.

Let’s start with the more common one: UL 924 applications. UL 924 devices are meant to be used in applications that take place downstream of a UL 1008 device. They are often used to bypass a wall switch or override a dimming signal on your emergency circuit in the event of normal power loss. Devices like this include modelsĀ ESR2401B and ESR2401D. Other more complicated versions of UL 924 devices, such as modelsĀ ESRN or ESRB, have 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, in addition to overriding both so that the emergency lights always come on at full brightness in an emergency situation. If you are installing lights, this is where you will be spending most of your time, and so in most situations a UL 924 device is what you will need. UL 924 devices do not, however, transfer power on the emergency circuit from normal to back-up. This is where UL 1008 devices come in.

UL 1008 devices are often called transfer switches. Transfer switches are used to transfer the power source of the emergency circuit from normal power to back-up power in the event of normal power loss. Typically, these are large and used to switch over entire buildings to back-up power. Sometimes a smaller transfer switch will be used to switch just a branch circuit of lights. These are called Branch Circuit Emergency Lighting Transfer Switches, or BCELTS for short. It’s these BCELTS that UL 924 devices often get confused for as they are closer to the same size. Some BCELTS on the market today even include a UL 924 rating, meaning they both transfer power and bring emergency lights on at full brightness. BCELTS are usually only used in a small amount of retrofit applications and it’s important that a UL 924 device isn’t used in its place.

In conclusion, if you have two power sources and one circuit that needs to switch between them, then use a UL 1008 device. If you’re just looking to override a switch or dimming signal so that an emergency light will come on full brightness, use a UL 924 device.

If you have questions, call us at tech support and we will do our best to point you in the right direction.


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About the Author

Tym Moore is an Electrical Engineer who hails from the best state of Colorado.
He graduated from Colorado State University in 2017 and moved to Indiana shortly afterward to marry his now wife. Outside of work, Tym spends most of his time driving back home, and complaining about how flat Indiana is.

Be sure to give Tym a call for tech support. He will always do his best to find a solution for you.