How to power emergency illumination systems

Emergency illumination insights

• Emergency illumination systems are required in most commercial buildings and are powered by an emergency power system.
• Various codes and standards define the performance of the emergency illumination system.

The design of emergency power systems for lighting necessitates a multifaceted approach, encompassing the careful selection of power sources, the establishment of robust wiring systems and the integration of effective controls. These components collectively ensure the system’s survivability and performance, adhering to the stipulations set forth by building codes and standards.

Emergency power systems play a critical role in ensuring the safety and functionality of emergency lighting within buildings. This article discusses the key design considerations for emergency power systems, with a focus on supporting emergency lighting. The National Fire Protection Association (NFPA) codes and standards serve as the primary source driving these designs, including:

• NFPA 70: National Electrical Code (NEC).
• NFPA 101: Life Safety Code.
• NFPA 110: Standard for Emergency and Standby Power Systems.
• NFPA 111: Standard on Stored Electrical Energy Emergency and Standby Power Systems.
• State and local building codes.

Sources of power for emergency illumination

Emergency illumination is needed for people to see how to safely egress a building in the event of an emergency such as a building fire or power loss from the electric utility. It is considered a life safety system.

Figure 1: Recessed style emergency lighting unit equipment. Courtesy: CDM Smith

The 2023 edition of NFPA 70, Article 700 requires that at least two sources of power must be provided for emergency lighting: One normal supply and one or more of the emergency systems listed in Article 700. The power source for emergency illumination must be available and supply power to the luminaire within 10 seconds after the loss of normal power supply. For certain building and occupancy types, the emergency power source must be located within spaces fully protected by approved fire suppression systems or within a two-hour fire-rated room.

Power sources for emergency illumination must be able to operate for a minimum of 90 minutes. Acceptable emergency power supply sources include the following:

• Battery equipped emergency luminaires : This is a built-in emergency battery integral to an architectural lighting fixture that meets UL 924 or UL 1008
• Unit equipment (see Figure 1): This is a standalone emergency battery unit with head lamps attached to the unit or remotely mounted. The unit can be installed via wall-or ceiling-mounts, recessed or

Figure 2: Lighting inverter with centralized storage battery. Courtesy: CDM Smith

Centralized storage battery (see Figure 2): Also called a lighting inverter, it has a larger battery size to serve multiple emergency light fixtures. This unit must meet the UL 924 standard.

• Uninterruptible power supplies (UPS, see Figure 3): Like the lighting inverter, the emergency UPS must be UL 924 listed and serve only emergency loads.
• Generator set (see Figure 4): Single or multiple generator engines and alternator sets connected to the facility emergency power distribution system and serving only emergency loads. The automatic transfer switch shall be UL 1008 listed.
• Other less typical emergency power supplies allowed by the NEC including battery energy storage systems, fuel cells, separate utility services (not from same utility substation) and microgrids.

When designing power for emergency illumination, it is important for the designer to determine the level, class and type of the emergency power supply system required for the installation in accordance with NFPA 110 or the local applicable codes. This is driven by local building codes based on the occupancy type.

For instance, Level 1, Class 2, Type 10 may be required for emergency lighting in convention centers. There are more considerations when designing emergency power source such as automatic transfer equipment, capacity and means of connecting temporary emergency sources. However, those requirements will not be discussed in this article.

Wiring for emergency illumination systems

Figure 3: Like the lighting inverter, the emergency uninterruptible power supply must be UL 924 listed and serve only emergency loads. Courtesy: CDM Smith

The wiring for emergency power, including branch circuits for lighting systems, shall generally be routed separately from normal facility power wiring and marked for identification as emergency. Emergency wiring circuits are required to be designed and located to minimize hazards that may contribute to failure, such as fire, flooding, icing, vandalism and other adverse conditions. One recommended practice is using red conduits or couplings, for emergency circuits. Another option is to use red box covers with panel names and circuit numbers indicated on the covers.

For specific occupancies as outlined in NEC 700.10(D)(2), such as assembly occupancies with greater than 1,000 occupants, buildings taller than 75 feet in height and educational occupancies with greater than 300 occupants, lighting system feeder-circuit wiring is required to be installed in separate rooms or spaces fully protected by an automatic fire protection system (such as a fire sprinkler) or be installed in a listed electrical protective system with a minimum two-hour fire rating.

Examples of electrical protective systems with a minimum two-hour fire rating may be identified in the UL Guide Information for Electrical Circuit Integrity Systems (FHIT). This system uses mineral-insulated cable as a primary component to achieve a two-hour fire rating.

Other ways to comply with NEC 700.10(D)(2) are to put the feeder in a two-hour fire-resistive assembly or encase it in two inches of concrete. Neither method will do what an electrical circuit protective system will do, which is maintain circuit operation during a fire. These methods may comply with the code but are ineffective at protecting circuits.

Battery-equipped luminaires, formerly called, ‘”unit equipment” in NEC, shall be connected to the same circuit that serves normal lighting in the area. The intent is that normal lighting fails while the normal source to battery-equipped luminaires fails, to ensure that the failure is noticeable to the building occupants.

Emergency system circuits for lighting

NEC Article 700 Part IV outlines many of the emergency system circuit requirements for emergency lighting systems.

Figure 4: Installed emergency generator set. Other less typical emergency power supplies allowed by the NFPA 70: National Electrical Code include battery energy storage systems, fuel cells, separate utility services (not from same utility substation) and microgrids. Courtesy: CDM Smith

A key requirement mandated in Part IV of Article 700 is that loads on emergency branch circuits shall be dedicated for emergency use. No normal lighting, equipment or appliances serving nonemergency loads may be connected to emergency lighting circuits. Separation of emergency lighting circuits from nonemergency circuits ensures that the integrity of systems, controls and physical assemblies that construct the emergency lighting circuits are maintained as designed and that their performance is as expected in a fire event.

Emergency illumination includes means of egress lighting, way-finding lighting and illuminated exit signs. The circuits serving emergency lighting systems shall work independently; failure of one emergency light fixture shall not leave a space in total darkness. This is a reliability requirement that facilitates emergency egress.

Branch circuits for emergency lighting shall be connected to an emergency power supply, independent of the normal power supply. It must automatically operate when there is a failure of the branch circuits supplying the normal lighting. A typical way of achieving this is with lighting inverters, emergency lighting units or UL 924 listed automatic load control relays.

Emergency lighting can also be supplied by a minimum of two branch circuits from separate and independent power sources. Emergency lighting can also be supplied by at least two branch circuits from separate and independent power sources. Means shall be provided for automatically energizing a system upon its failure.

Controlling emergency illumination circuits

Switch-controlled emergency lighting circuits shall be controlled by only authorized personnel. The design will include an emergency lighting transfer device that meets UL 924 or UL 1008 to switch power to an emergency circuit that serves emergency light fixtures. The transfer device will automatically switch power to the emergency source and bypass the switch control upon failure of normal power.

However, the branch circuit for emergency lighting with a lighting transfer switch shall not be rated greater than 20 amps.

For lighting control systems that use automatic load control relays, only the listed automatic load control relays are allowed to energize emergency lighting.

Do you have experience and expertise with the topics mentioned in this content? You should consider contributing to our WTWH Media editorial team and getting the recognition you and your company deserve. Click here to start this process.