The history of emergency lighting codes in the United States is generally traced back to the horrific fire disaster at the Triangle Shirtwaist Factory in 1911. Partly due to the absence of emergency lighting and exit signs, 146 employees lost their lives. In the century since that fire, emergency lighting codes have continued to evolve as electrical and lighting technology have advanced.
A component of that evolution has been the requirements for the power supplied to emergency lighting. Emergency lighting is an essential aspect of safety for building occupants, providing illumination in the event of power outages or emergencies. Recognizing that reliability is critical for these systems, many jurisdictions require emergency lighting systems to be on dedicated circuits.
Dedicated Circuits Ensure Emergency Lights Remain Illuminated
Emergency lighting systems exist to facilitate safe evacuation and navigation during emergencies. By mandating dedicated circuits for emergency lighting, regulatory bodies aim to guarantee the uninterrupted operation of these systems. Dedicated circuits ensure that emergency lights remain powered even if other electrical circuits fail due to overload, faults, or maintenance issues.
Dedicated circuits for emergency lighting involve separate wiring and circuitry, distinct from general-purpose lighting and power systems. This separation minimizes the risk of shared failures that could compromise emergency illumination. Emergency lighting circuits are typically designed with redundancy and backup batteries or generators to enhance reliability.
The National Electric Code (NEC) explains emergency lighting systems are intended to supply illumination or power automatically, or both, to designated areas and equipment in the event of failure of the regular power source or if an accident interrupts elements of a system intended to supply.
According to NEC 700-16, emergency illumination includes all forms of egress lighting, illuminated exit signs, and all other light fixtures necessary to provide illumination. Emergency lighting systems are required to be designed so that the failure of any individual lighting component will not leave required egress paths in darkness.
Looking closer at the requirements, NEC 700-9 details that two or more emergency circuits may be wired in a shared raceway, cable box, or cabinet. The code also states that wiring from an emergency source is to be kept entirely independent of all other wiring equipment unless specific situations exist:
- Wiring from the power source is located in transfer equipment enclosures
- Wiring is supplied from two sources in exit or emergency luminaires (lighting fixtures)
- Wiring is from two sources in a shared junction box, attached to exit or emergency fixtures
- The wiring is within a shared junction box attached to the unit equipment, containing only the branch circuit supplying the unit equipment and the emergency circuit supplying the unit equipment.
Additionally, NEC 700-15 stipulates that no appliances or lamps, except those required for emergency use, shall be supplied by emergency lighting power circuits.
In summary, emergency lighting components are required to utilize dedicated circuits. This dedicated power enables constant illumination during an emergency. The technical separation of emergency lighting from general-purpose electrical systems enhances reliability, clarity, and maintenance efficiency.
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