UL 924

Lighting Inverter Supply only works with UL 924 standard, tested, and certified systems, providing you with the industry’s highest capacity and efficiency systems. 90-minute lighting inverter systems provide industry-wide solutions for the current UL 924 standard. Article 700 or 701 of the National Electrical Code, NFPA 70, the Life Safety Code, NFPA 101, the Fire Code, NFPA 1, the International Building Code, IBC, and the International Fire Code, IFC.


Inverters help provide uninterrupted power to lighting systems in the event of an outage. This is important for facilities because emergency lighting must remain lit for at least 90 minutes when the power goes out. They also help facilities meet NFPA’s life safety requirements and UL’s 924 code, two standards your systems must meet.


You can buy emergency lighting units with backup batteries, which can meet the requirements without an inverter. Depending on the size and makeup of your facility, you may need more power to meet demand. Usually this comes from a backup generator or battery sets connected via diodes. The inverter helps provide power by converting electricity to a useable format. Facilities use alternating current, while the backup (emergency) power generally comes from a direct current. The inverter will convert the DC power to an alternating current, allowing your facility to continue functioning as it had before the outage.


The costs of inverters can vary from hundreds to thousands of dollars. You may easily be able to get by with a low cost solution, but before you decide, it’s good to get a second opinion before making a big investment. Whether you want to go at the shopping process alone or consult a guide, you should ensure each inverter you look has two very important listings: NFPA 101 and UL 924. To meet inspection and avoid liability, your backup power system will need to at a minimum pass these codes.

Members of our team are available to assist in the system selection process. You may provide a specification to us to review with you. You may need a walk through with an Electrical contact either provided by us or your own. We will assist every step of the way. Sizing review, voltage selection, Battery Runtime options are all important variables in the selection process. Proper documentation of System manuals and technical information are an integral part of the process so that the installation technician or contractor can properly plan and estimate the project.

90 minute battery runtime requirement

UL 924 certified lighting inverters must adhere to the NFPA Life Safety code 101 which requires the battery system provide uptime via battery runtime of 90 minutes, (1.5 hours). The requirement provides that the emergency power system restore lighting within 10 seconds after loss of normal power, and for a duration of 90 minutes from that time.  This is defined by standard NFPA 101 Systems shall be of the Type 10, Level 1 System, and Class 1.5. 

The requirement for illumination provides for 1fc level average illumination , and 0.1 fc. minimum of Illumination level and is allowed to decline to 0.6 fc average. 0.06 fc minimum is required at the end of the 90 minute duration. .

Batteries may be on board in an emergency light direct system. For central lighting inverters VRLA or lithium ion batteries produce the power at the central inverter, they are then hardwired throughout facility to the emergency lights and illumination areas. This provides several benefits.

Benefits of a Central Battery Inverter System

-A Central Battery Inverter System provides for simple maintenance in one location, vs. multiple to hundreds of physical points to maintain and oversee.

-All batteries are located in the Central Inverter for access, replacement and voltage checks.

-One communications system to monitor and respond to.

-Increased options for software, notifications, remote monitoring, and data logging.

-Provides ability to use various battery options such as lithium ion, Pure Lead Batteries, and VRLA (Valve Regulated Lead Acid).

Benefits of Lithium Ion Batteries for Central Inverter Systems

UL 924 UPS systems and central Lighting Inverters also work with longer runtime lithium ion battery systems to achieve the 90 minute runtime. Lithium batteries provide much less maintenance attention and a longer physical life of the batteries. The following are benefits to a lithium ion battery for Central Inverters.

-The physical life of the battery may be extended to 12-15 years, vs. traditional VRLA battery life of 3-5 years.

-The battery does not require a physical measurement to maintain it. Therefore frequent technician maintenance visits are not required.

-The batteries provide much more detailed information about themselves in real time to flag any problems. The notification of issues is much more immediate and pronounced.

-Batteries are much less physical footprint, as much as 30% of a VRLA physical footprint.

-Lithium Ion batteries shed much less heat in terms of BTU, less ventilation and attention to physical room cooling hvac.

Challenges still remain with certain OEM’s to provide lithium ion systems for general products. The shorter duration load support that lithium provides requires an oversizing of the battery system. The offset of higher capital cost up front, vs. lower annual maintenance over 10 plus years is the valuation calculation customers need to perform.

VRLA vs. Lithium ION vs. Pure Lead Batteries for Central Inverters

Customer are seeking newer technologies. The VRLA (Valve Regulated Lead Acid) Battery has been the standby in the industry for 50 plus years. The industry is just now providing the ability to combine Lithium Ion Batteries with Central Inverter Systems. Old tech meets new tech when comparing Pure Lead batteries and lithium. Below provides some detail of those options which may be readily available or upcoming for the central inverter industry.

VRLA Batteries = Lower Capital cost up front, higher attention to maintenance annually, more frequent replacement. (Life 3-5 Years)

VRLA batteries inherent nature is to degrade over time. This non-linear degradation requires them to be physically tested quarterly or semi-annually. In the case of a central inverter or a UL924 UPS system, it is a string of batteries. Because all batteries degrade at different rates, any decline acceleration of a single cell or battery affects all the others. For this reason frequent checks on the battery float voltage are required. Also for this reason, if a single cell is bad it must be removed and replaced immediately in order to not affect the whole string of batteries. The VRLA battery is currently the standard for central inverter systems.

Lithium Ion Batteries = Higher Capital cost up front, low attention to maintenance, long battery life duration (10-15 Years)

Much the opposite of a VRLA battery, the lithium ion battery maintains a general stable state over it’s life. It does not require the frequent checks regarding it’s voltage. It very much acts like binary computer with 1’s and 0’s. It can either be operating very well, or not. Because they intrinsically have very comprehensive monitoring systems, it will tell you when it is not. A lithium ion battery system that is set for standby applications for a Central Inverter System is not called on frequently to operate. Therefore constant discharge and re-charging should not be a frequent part of it’s life. This makes it a very stable storage system for a Central Inverter System solution long term. Current uses of lithium ion systems for cars, cell phones, and other consumables call on them frequently to discharge and re-charge. The momentary or 90 minute requirement of an outage for a central inverter system currently is only a couple times a year if any. However there are still challenges regarding packaging the lithium systems with Central Inverters mainly to achieve the 90 minute runtime. Talk to your LIS representative to see which sizes and models of inverter systems may be tied to a lithium ion battery plant.

Pure Lead Batteries = Mid Range Capital cost comparably, medium attention to maintenance annually, long battery life duration (8-10 Years)

Pure lead batteries are not new, and have traditionally been used for larger industrial or large physical battery plant with emergency generator applications. They operate and degrade in much the same way as a VRLA battery. They provide for about double the life of a VRLA. The do not require as much touch maintenance as VRLA but do require annual measurements. The components of Pure Lead and other materials provide for a more industrial, and longer lasting battery. Pure lead batteries are not used in smaller or even mid-sized central inverter systems. As an industry they can provide for an inverter system in a physical plant, large hospital, university, or campus office environment with many buildings connected to a central inverter system. Large applications that choose to use a generator and a large physical battery plant to achieve the cutover and runtime for UL 924 and Life Safety 101 can use Pure Lead batteries in conjunction with an automatic switching generator. Seek local codes and professional MEP design for these applications.