NFPA 101, the Life Safety Code, and the International Building Code (IBC) require emergency lighting in all commercial and industrial buildings to facilitate emergency egress of people from the building and to reduce the possibility of panic in buildings during the exiting of large numbers of people during an emergency. While NFPA 101 and the IBC require emergency lighting, the National Electrical Code (NEC) defines the type of electrical equipment that can be used for emergency lighting and the installation requirements for the circuits supplying the emergency equipment. Many local and some national codes require energy savings for all lighting in a building, so providing an automatic load controller where lighting can be switched off will permit compliance with energy-savings features for a building, while still maintaining the life safety aspects of emergency lighting. Automatic load-control relays are now permitted in the 2011 NEC to help comply with energy-savings requirements in local codes and in reconnecting emergency loads.
Emergency lighting loads must be automatically energized or re-energized within 10 seconds of the electrical power outage, based on 700.12 of the NEC, and must stay energized for at least 90 minutes or for the anticipated time of the building evacuation. Unit equipment or battery-pack lighting is often used to provide the temporary lighting during power outage. Unit equipment is covered in 700.12(F) and consists of a rechargeable battery, a battery charger, provisions for one or more lamps mounted on the unit equipment, provisions for remote lamps powered from the unit equipment, and a relaying device that will energize the unit equipment lamps upon failure of the lighting branch circuit. The batteries must have a suitable rating and capacity to supply and maintain at least 87.5 percent of the nominal battery voltage of the total lamp load of the unit equipment for at least 1.5 hours, or the unit equipment must supply and maintain not less than 60 percent of the initial level of emergency illumination for at least 1.5 hours.
Where unit equipment is not used for emergency illumination or is not the sole source of emergency illumination, an additional source of electrical power may be provided using an uninterruptible power supply (UPS), a generator, a fuel cell, or a separate service used to supply emergency lighting. With this method of emergency lighting, selected branch circuits can be automatically switched from normal power to emergency power upon loss of normal power by a transfer switch that is electrically operated and mechanically held in accordance with 700.5. In addition, the transfer switch is required to be listed for emergency use based on UL 1008, the standard for transfer switches, and must be approved for this application by the authority having jurisdiction as noted in 700.5(A) and (C). Where transfer switches are used for emergency lighting and power, the transfer equipment must only be used for emergency loads based on 700.5(D). All wiring from emergency sources must be kept entirely independent of all other wiring and equipment, unless in accordance with 700.10(B)(1) through (5).
Part V of Article 700 indicates switches installed in emergency lighting circuits must be arranged so that only authorized people have control of emergency lighting. This ensures that the emergency lighting circuits are not inadvertently turned off, thereby disabling the lighting. Switches connected in series or three- or four-way switches are not permitted in emergency lighting circuits. Additional switches that act only to put emergency lights into operation, but not disconnect them, are permitted. A dimmer system containing more than one dimmer and listed for use in emergency systems is permitted as a control device for energizing emergency lighting circuits. Upon failure of the normal source of electrical power, this dimmer system is permitted to selectively energize only those branch circuits required to provide minimum emergency illumination.
In addition to the other lighting control requirements, 700.24 in the 2011 NEC permits a listed automatic load control relay (ALCR) to automatically energize the emergency lighting load upon loss of the normal power supply. Section 700.2 defines an ALCR as a device used to energize switched or normally off lighting equipment from an emergency supply in the event of loss of the normal supply and to de-energize or return the equipment to normal status when the normal supply is restored. While an ALCR can be used for shunting around a control device and re-energizing a circuit that was intentionally turned off or dimmed, it is still required to be connected to a single source of emergency supply. As noted in 700.24, an ALCR shall not be used as transfer equipment and does not replace the need for a transfer switch at the point of connection to two sources of supply.
ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and email@example.com.