Adoption and use of the 2014 National Electrical Code (NEC) is underway in many areas of the country. Adoption processes and timelines can vary between states and jurisdictions. With the 2014 NEC, a few additional requirements apply to emergency systems. Article 700 of the Code contains the minimum requirements for emergency systems. Because these are the minimum, one must do at least that much. Let’s take a look at three rules that must be applied where the new edition of the Code is adopted and enforced.


Surge protection


The first requirement to discuss is located in a new Section 700.8. It requires a listed surge-protective device (SPD) to be installed in or on all emergency system switchboards and panelboards. The proper type and rating of the SPD is essential, and the device must be suitable for the application. This requirement will help ensure emergency electrical-distribution systems continue to deliver reliable power to vital life-safety loads in the event of a voltage spike.


Voltage surges resulting from lightning strikes or due to various sources within an electrical system, such as switching of powered electronic devices, can destroy the electrical distribution equipment and the loads it supplies. Electrical equipment damage can occur from a single lightning strike nearby or the accumulative effects of multiple voltage surges from sources within an electrical system. Because SPDs are required to be listed, they include specific installation instructions that must be followed. It is important for electrical contractors to include SPDs and wiring for emergency panelboards and switchboards that are designated as emergency when designing and bidding on projects that include emergency systems.


Emergency system unit equipment


The revision to the exception following Section 700.12(F) contains another new requirement. The change deals with installation and use of unit equipment as the emergency illumination. Emergency lighting ensures egress illumination when the normal electrical supply is interrupted. An existing exception permitting unit equipment supplied by three or more normal circuits no longer allows multiwire branch circuits to serve the supplied area. Using normal multiwire branch circuits increases the risk of an area being without emergency lighting.


Before emergency-egress lighting operates, the lighting loss must be sensed or determined. Then, automatic action is employed to ensure emergency lighting is provided in proper areas. Where standard 1½-hour battery-unit equipment provides emergency lighting, these units normally sense loss of a branch circuit or a phase of a feeder, such as 120 or 277 volt (V). For most egress areas, this power-loss sensing works well. However, for three-phase lighting circuit areas, it is problematic.


Section 210.4(B) requires each multi­wire branch circuit to be provided with a means to simultaneously disconnect all ungrounded conductors at the branch-circuit origin. This can be done using multipole breakers or single-pole breakers with identified handle ties. If a multiwire branch circuit is used to comply with this exception, there is an increased possibility of leaving the area in total darkness if one circuit were to trip and cause the others to open. This revision restricts multiwire branch circuits from being used to comply with the exception and seeks to improve consistency with other NEC rules that restrict multiwire branch circuits in areas where similar hazards have been identified, such as 517.18(A) and 517.19(A).


Multiwire branch circuits


The third change involves a new Section 700.19. Article 700 no longer permits multiwire branch circuits protected by common trip circuit breakers or single-pole breakers connected by identified handle ties to serve emergency lighting and power circuits. The reason is emergency lighting and power could be interrupted or unavailable during ordinary line-to-ground faults and other problems where common trip circuit breakers or handle ties are employed. Reliability and power continuity for emergency circuits were the main drivers for this revision.


The revision reduces risks by preventing the unnecessary opening of the other one or two poles of a multiwire branch circuit because of an overload, ground fault or short circuit on any one pole of the multiwire branch circuit. For example, reliability is certainly decreased if a short circuit or ground-fault event in a 277V lighting ballast takes out the other two poles of a three-pole circuit breaker, interrupting the other two emergency lighting circuits. Branch circuits supplying emergency lighting and power require their own neutral conductor and must not be part of a multiwire branch circuit.


It should also be noted that, per 240.15(B)(3), a multiwire branch circuit supplying 277V lighting requires a common trip circuit breaker, which results in the loss of multiple lighting branch circuits when one circuit is subjected to a ground-fault, short-circuit or even overcurrent.


Conclusion


These revisions provide an improvement in ensuring power continuity for emergency systems. Refer to the 2014 NEC for more information and the exact language related to these changes.