700.16 Emergency Illumination. Emergency illumination shall include all required means of egress lighting, illuminated exit signs, and all other lights specified as necessary to provide required illumination.
Emergency lighting systems shall be designed and
installed so that the failure of any individual lighting
element, such as the burning out of a lamp, cannot
leave in total darkness any space that requires
emergency illumination.
Where high-intensity discharge lighting such as high-and low-pressure sodium, mercury vapor, and metal halide is used as the sole source of normal illumination, the emergency lighting system shall be required to operate until normal illumination has been restored.
Exception: Alternative means that ensure emergency lighting illumination level is maintained shall be permitted.
700.17 Circuits for Emergency Lighting. Branch circuits that supply emergency lighting shall be installed to provide service from a source complying with 700.12 when the normal supply for lighting is interrupted. Such installations shall provide either of the following:
(1) An emergency lighting supply, independent of the general lighting supply, with provisions for automatically transferring the emergency lights upon the event of failure of the general lighting system supply
(2) Two or more separate and complete systems with independent power supply, each system providing sufficient current for emergency lighting purposes
Unless both systems are used for regular lighting purposes and are both kept lighted, means shall be provided for automatically energizing either system upon failure of the other. Either or both systems shall be permitted to be a part of the general lighting system of the protected occupancy if circuits supplying lights for emergency illumination are installed in accordance with other sections of this article.
700.18 Circuits for Emergency Power. For branch cir cuits that supply equipment classed as emergency, there shall be an emergency supply source to which the load will be transferred automatically upon the failure of the normal supply.
V. Control — Emergency Lighting Circuits
700.20 Switch Requirements. The switch or switches in stalled in emergency lighting circuits shall be arranged so that only authorized persons have control of emergency lighting.
Exception No. 1: Where two or more single-throw switches are connected in parallel to control a single circuit, at least one of these switches shall be accessible only to authorized persons.
Exception No. 2: Additional switches that act only to put emergency lights into operation but not disconnect
them shall be permissible.
Switches connected in series or 3- and 4-way switches shall not be used.
700.21 Switch Location. All manual switches for control ling emergency circuits shall be in locations convenient to authorized persons responsible for their actuation. In facilities covered by Articles 518 and 520, a switch for controlling emergency lighting systems shall be located in the lobby or at a place conveniently accessible thereto.
In no case shall a control switch for emergency lighting be placed in a motion-picture projection booth or on a stage or platform.
Exception: Where multiple switches are provided, one such switch shall be permitted in such locations where arranged so that it can only energize the circuit but cannot de-energize the circuit.
700.22 Exterior Lights. Those