How Does a Backup Driver Work?
An emergency backup driver provides backup power to lighting systems during power outages. To do this, backup drivers monitor the power line for any disruptions. If the driver detects an outage, it automatically switches power from the main supply to the battery to provide the light fixture with enough power to remain “On.” This energy change must not last more than 10 seconds, as mandated by the National Fire Protection Association (NFPA). The NFPA also requires various commercial and residential structures to utilize emergency drivers, including certain underground and high-rise buildings, to meet compliance codes. Emergency drivers can be wired to the existing driver or light fixture in various ways depending on the type of backup driver and output voltage.
Types of Emergency Backup Drivers
High-Voltage LED Emergency Drivers
High-voltage output LED backup drivers are wired between the main power line and the light fixture inputs. During emergency operations, the driver supplies high-voltage DC output to the light fixture. This type of backup driver often requires a 0-10V dimmable LED fixture to prevent the battery from rapidly draining energy during emergency operations.
Low-Voltage LED Emergency Drivers
Low-voltage backup drivers take over for the existing driver during power outages. Wiring these types of drivers is typically more complex since the output of the emergency driver must be directly connected to the LEDs. To determine which driver you need, you need a battery with a voltage ranger the same or larger than the existing driver’s output voltage.
All-in-One Emergency Drivers
Instead of the emergency driver supplying battery power to the light fixture, all-in-one battery backup kits feature a compact LED array that is illuminated instead. These types of drivers are usually installed in troffer and linear strip fixtures. The LED array and emergency driver have their own circuit board and function separately from the light.
Emergency Drivers for Specific Light Fixtures
Most battery backups are installed in the light fixture housing, meaning that lights with a slim profile will require compact drivers. Troffer, fluorescent, and flat panel lights typically need slim emergency drivers or all-in-one battery backup lighting kits that can fit inside the housing. Single-point hanging lights, such as UFO high bays, use specialized drivers that are designed to hang the light fixture from its integrated hook. Given the required power output, UFO high bay emergency drivers are typically bulky and heavy and cannot be placed inside the fixture housing.
Accessible Test Indicators
All emergency drivers are required to have manual test switches, as mandated by UL 924. Various test button options are available based on the fixture and mounting location, including wall-mounted test indicators, ceiling-mounted test indicators, and test buttons that integrate into the light fixture. Emergency backup kits for high bays or highly mounted lights commonly come with a remote-controlled testing button. This allows you to easily test the emergency system without needing a ladder or scissor lift to access the test button.
National Fire Protection Association Requirements
The National Fire Protection Association (NFPA) Life Safety Code 101 lists requirements for emergency lighting systems, including emergency drivers. All emergency drivers must meet the following specifications listed in NFPA 101 Section 7.9:
- Emergency drivers must provide at least 90 minutes of backup power
- Initial backup power illumination must average 1 ft-candle but no less than 0.1 ft-candle along the floor level of the egress. At 90 minutes, backup power illumination must average 0.6 ft-candle but no less than 0.06 ft-candle at any distance along the egress
- Emergency backup battery systems must be listed to UL 924
- Testing for self-diagnostic battery-operated emergency lighting equipment must be conducted at least every 30 days for at least 30 seconds. Visual tests shall be conducted no less than once every 30 days, and annual functional testing must last at least 90 minutes
- A status indicator on the driver should clearly show testing failures
- Emergency drivers must always be in operation or be automatically turned on
