Lighting Applications: UL 924 vs. UL 1008

Lighting systems in commercial and industrial buildings must not only provide reliable illumination, but also meet strict safety and code requirements. Two critical UL standards — UL 924 and UL 1008 — govern different aspects of emergency and transfer power systems, yet they are often confused or misunderstood. Understanding the distinctions between these standards, however, is essential for facility managers to ensure code compliance, maintain occupant safety, and select the right equipment for each lighting application.

While taking tech calls here in Indiana, we’re often asked about the difference between UL 924 and UL 1008, which is understandable seeing as they both deal with emergency lighting and their construction is very similar. However, using one in place of the other won't sit well with the inspector when they drop by, so let’s dive into what these UL standards are and the very crucial differences between the two.

Functional Devices is obsessed with not only creating quality products, but also building components that meet strict requirements. Explore our UL-rated emergency lighting controls and reach out if you need help making the right selection.

What Is UL 924?

Let's start with the more common one: UL 924 and its applications. 

UL 924 covers emergency lighting and power equipment, ensuring that exit signs, emergency luminaires, and battery-backed lighting operate correctly during power outages.

UL 924 devices 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 models ESR2401B and ESR2401D. 

Other more complicated versions of UL 924 devices, such as models 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.

What Is UL 1008?

UL 1008 focuses on automatic transfer switches, and in fact, 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. This means they both transfer power and bring emergency lights on at full brightness. BCELTS are usually only used in a small amount of retrofit applications. It's important that a UL 924 device isn't used in its place.

Key Differences Between UL 924 and UL 1008

UL 924 and UL 1008 serve distinct purposes in lighting and power systems, and understanding these differences is critical for proper design and compliance. UL 924 specifically focuses on the performance of the lighting devices themselves, including battery duration, automatic switching, and emergency illumination levels.

UL 1008, in contrast, governs transfer switches, and its primary concern is system-level reliability, including switching speed, contact ratings, and coordination with upstream and downstream equipment. Here’s a table to easily compare:

While UL 924 ensures individual emergency lighting works during an outage, UL 1008 ensures that the building’s power distribution infrastructure can maintain service to critical circuits. UL 924 devices are meant to be used in applications that take place downstream of a UL 1008 device. 

Designers and engineers must consider both standards when creating a fully code-compliant emergency lighting system, as using the wrong equipment or neglecting either standard can compromise safety, performance, and regulatory compliance.

Frequently Asked Questions About UL 924 and UL 1008

Q: Are UL 924 and UL 1008 required by building codes?

A: Many local building codes and the National Electrical Code (NEC) reference these standards. UL 924 is typically required for emergency lighting systems, while UL 1008 is required for automatic transfer switches in critical power applications.

Q: Can equipment be UL listed for both standards?

 A: Some integrated systems combine emergency lighting and transfer switch functionality, but each component is generally tested separately for its respective UL standard.

Q: How often should UL 924 and UL 1008 equipment be tested?

A: Emergency lighting devices under UL 924 should be tested monthly and annually per NEC guidelines. UL 1008 transfer switches should be tested according to manufacturer recommendations and local code requirements, often annually.

Q: Do UL 924 or UL 1008 standards cover energy efficiency?

A: No, both focus on safety and reliability, not energy savings. Separate certifications or standards address efficiency.

Q: Can UL 1008 switches be used with renewable power sources?

A: Yes, as long as the switch meets voltage, frequency, and load specifications for the connected sources, including generators, solar inverters, or battery systems.

Lighting for Emergencies from Functional Devices

If you have two power sources and a single circuit that needs to switch seamlessly between them, a UL 1008 device is the correct choice. These automatic transfer switches ensure reliable power transfer to critical systems during an outage, protecting both equipment and occupants. On the other hand, if your goal is simply to override a switch or dimming signal so that an emergency light operates at full brightness, a UL 924 device is the appropriate solution. It guarantees that emergency lighting will function as intended when it’s needed most.

Selecting the right UL-rated device is essential for safety, code compliance, and system reliability. If you’re unsure which solution is best for your application, our team at Functional Devices is here to help. Contact us, and we will provide guidance to ensure you choose the right equipment for your specific lighting and power needs.

About Functional Devices, Inc.

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.