Menu

Article 701

Legally Required Standby Systems

Part I. General

  1. Scope. The provisions of this article apply to the electri‐ cal safety of the installation, operation, and maintenance of legally required standby systems consisting of circuits and equipment intended to supply, distribute, and control electric‐ ity to required facilities for illumination or power, or both, when the normal electrical supply or system is interrupted.The systems covered by this article consist only of those that are permanently installed in their entirety, including the power source.Informational Note No. 1: For further information, see NFPA 99-2015, Health Care Facilities Code.Informational Note No. 2: For further information regarding performance of emergency and standby power systems, see NFPA 110-2013, Standard for Emergency and Standby Power Systems.Informational Note No. 3: For further information, see ANSI/ IEEE 446-1995, Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications.
  2. Definition.Legally Required Standby Systems. Those systems required and so classed as legally required standby by municipal, state, federal, or other codes or by any governmental agency having jurisdiction. These systems are intended to automatically supply power to selected loads (other than those classed as emergency systems) in the event of failure of the normal source.
    Informational Note: Legally required standby systems are typi‐ cally installed to serve loads, such as heating and refrigeration systems, communications systems, ventilation and smoke removal systems, sewage disposal, lighting systems, and indus‐ trial processes, that, when stopped during any interruption of the normal electrical supply, could create hazards or hamper rescue or fire-fighting operations.
  3. Tests and Maintenance.
    1. Conduct or Witness Test. The authority having jurisdic‐ tion shall conduct or witness a test of the complete system upon installation.
    2. Tested Periodically. Systems shall be tested periodically on a schedule and in a manner acceptable to the authority having jurisdiction to ensure the systems are maintained in proper operating condition.
    3. Maintenance. Legally required standby system equipment shall be maintained in accordance with manufacturer instruc‐ tions and industry standards.
    4. Written Record. A written record shall be kept on such tests and maintenance.
    5. Testing Under Load. Means for testing legally required standby systems under load shall be provided.
    Informational Note: For information on testing and mainte‐ nance of emergency power supply systems (EPSSs), see NFPA 110-2013, Standard for Emergency and Standby Power Systems.
  4. Capacity and Rating. A legally required standby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time. Legally required standby system equipment shall be suitable for the maximum available fault current at its terminals.The legally required standby alternate power source shall be permitted to supply both legally required standby and optional standby system loads under either of the following conditions:
    1. Where the alternate source has adequate capacity to handle all connected loads
    2. Where automatic selective load pickup and load shedding is provided that will ensure adequate power to the legally required standby circuits
  5. Transfer Equipment.
  1. General. Transfer equipment, including automatic trans‐ fer switches, shall be automatic and identified for standby use and approved by the authority having jurisdiction. Transfer equipment shall be designed and installed to prevent the inad‐ vertent interconnection of normal and alternate sources of supply in any operation of the transfer equipment. Transfer equipment and electric power production systems installed to permit operation in parallel with the normal source shall meet the requirements of Article 705.
  2. Bypass Isolation Switches. Means to bypass and isolate the transfer switch equipment shall be permitted. Where bypass isolation switches are used, inadvertent parallel operation shall be avoided.
  3. Automatic Transfer Switches. Automatic transfer switches shall be electrically operated and mechanically held. Automatic transfer switches shall be listed for emergency use.
    1. ARTICLE 701 — LEGALLY REQUIRED STANDBY SYSTEMS
      imageN
  4. Documentation. The short-circuit current rating of the transfer equipment, based on the specific overcurrent protec‐ tive device type and settings protecting the transfer equipment, shall be field marked on the exterior of the transfer equip‐ ment.
  1. Signals. Audible and visual signal devices shall be provi‐ ded, where practicable, for the purposes described in 701.6(A), (B), (C), and (D).
    1. Malfunction. To indicate malfunction of the standby source.
    2. Carrying Load. To indicate that the standby source is carrying load.
    3. Not Functioning. To indicate that the battery charger is not functioning.Informational Note: For signals for generator sets, see NFPA 110-2013, Standard for Emergency and Standby Power Systems.
    4. Ground Fault. To indicate a ground fault in solidly groun‐ ded wye, legally required standby systems of more than
    150 volts to ground and circuit-protective devices rated 1000 amperes or more. The sensor for the ground-fault signal devices shall be located at, or ahead of, the main system discon‐ necting means for the legally required standby source, and the maximum setting of the signal devices shall be for a ground- fault current of 1200 amperes. Instructions on the course of action to be taken in event of indicated ground fault shall be located at or near the sensor location.For systems with multiple emergency sources connected to a paralleling bus, the ground fault sensor shall be permitted at an alternate location.Informational Note: For signals for generator sets, see NFPA 110-2013, Standard for Emergency and Standby Power Systems.
  2. Signs.
  1. Mandated Standby. A sign shall be placed at the service entrance indicating type and location of each on-site legally required standby power source.Exception: A sign shall not be required for individual unit equipment as specified in 701.12(G).
  2. Grounding. Where removal of a grounding or bonding connection in normal power source equipment interrupts the grounding electrode conductor connection to the alternate power source(s) grounded conductor, a warning sign shall be installed at the normal power source equipment stating:

WARNING

SHOCK HAZARD EXISTS IF GROUNDING ELECTRODE CONDUCTOR OR BONDING JUMPER CONNECTION IN THIS EQUIPMENT IS REMOVED WHILE ALTERNATE SOURCE(S) IS ENERGIZED.

The warning sign(s) or label(s) shall comply with 110.21(B).

Part II. Circuit Wiring

701.10 Wiring Legally Required Standby Systems. The legally required standby system wiring shall be permitted to occupy the same raceways, cables, boxes, and cabinets with other general wiring.

Part III. Sources of Power

701.12 General Requirements. Current supply shall be such that, in the event of failure of the normal supply to, or within, the building or group of buildings concerned, legally required standby power will be available within the time required for the application but not to exceed 60 seconds. The supply system for legally required standby purposes, in addition to the normal services to the building, shall be permitted to comprise one or more of the types of systems described in 701.12(A) through (F). Unit equipment in accordance with 701.12(G) shall satisfy the applicable requirements of this article.

In selecting a legally required standby source of power, consideration shall be given to the type of service to be rendered, whether of short-time duration or long duration.

Consideration shall be given to the location or design, or both, of all equipment to minimize the hazards that might cause complete failure due to floods, fires, icing, and vandal‐ ism.

Informational Note: For further information, see ANSI/IEEE 493-2007, Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems.

  1. Storage Battery. Storage batteries shall be of suitable rating and capacity to supply and maintain the total load for a minimum period of 11∕2 hours without the voltage applied to the load falling below 871∕2 percent of normal. Automotive-type batteries shall not be used.•An automatic battery charging means shall be provided.
  2. Generator Set.
    1. Prime Mover-Driven. For a generator set driven by a prime mover acceptable to the authority having jurisdiction and sized in accordance with 701.4, means shall be provided for automatically starting the prime mover upon failure of the normal service and for automatic transfer and operation of all required electrical circuits. A time-delay feature permitting a 15-minute setting shall be provided to avoid retransfer in case of short-time re-establishment of the normal source.
    2. Internal Combustion Engines as Prime Mover. Where internal combustion engines are used as the prime mover, an on-site fuel supply shall be provided with an on-premises fuel supply sufficient for not less than 2 hours of full-demand opera‐ tion of the system. Where power is needed for the operation of the fuel transfer pumps to deliver fuel to a generator set day tank, the pumps shall be connected to the legally required standby power system.
    3. Dual Supplies. Prime movers shall not be solely depend‐ ent on a public utility gas system for their fuel supply or on a municipal water supply for their cooling systems. Means shall be provided for automatically transferring one fuel supply to another where dual fuel supplies are used.Exception: Where acceptable to the authority having jurisdiction, the use of other than on-site fuels shall be permitted where there is a low probability of a simultaneous failure of both the off-site fuel delivery system and power from the outside electrical utility company.
    4. Battery Power. Where a storage battery is used for control or signal power or as the means of starting the prime mover, it shall be suitable for the purpose and shall be equipped with an automatic charging means independent of the generator set.ARTICLE 702 — OPTIONAL STANDBY SYSTEMS 702.1
    5. Outdoor Generator Sets. Where an outdoor housed generator set is equipped with a readily accessible disconnect‐ ing means in accordance with 445.18, and the disconnecting means is located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure. Where the generator supply conduc‐ tors terminate at a disconnecting means in or on a building or structure, the disconnecting means shall meet the require‐ ments of 225.36.
  3. Uninterruptible Power Supplies. Uninterruptible power supplies used to provide power for legally required standby systems shall comply with the applicable provisions of 701.12(A) and (B).
  4. Separate Service. Where approved, a separate service shall be permitted as a legally required source of standby power. This service shall be in accordance with the applicable provisions of Article 230, with a separate service drop or lateral or a separate set of overhead or underground service conduc‐ tors sufficiently remote electrically and physically from any other service to minimize the possibility of simultaneous inter‐ ruption of supply from an occurrence in another service.
  5. Connection Ahead of Service Disconnecting Means. Where acceptable to the authority having jurisdiction, connec‐ tions located ahead of and not within the same cabinet, enclo‐ sure, vertical switchgear section, or vertical switchboard section as the service disconnecting means shall be permitted. The legally required standby service shall be sufficiently separated from the normal main service disconnecting means to mini‐ mize simultaneous interruption of supply through an occur‐ rence within the building or groups of buildings served.Informational Note: See 230.82 for equipment permitted on the supply side of a service disconnecting means.
  6. Fuel Cell System. Fuel cell systems used as a source of power for legally required standby systems shall be of suitable rating and capacity to supply and maintain the total load for not less than 2 hours of full-demand operation.Installation of a fuel cell system shall meet the requirements of Parts II through VIII of Article 692.Where a single fuel cell system serves as the normal supply for the building or group of buildings concerned, it shall not serve as the sole source of power for the legally required standby system.
  7. Unit Equipment. Individual unit equipment for legally required standby illumination shall consist of the following:
    1. A rechargeable battery
    2. A battery charging means
    3. Provisions for one or more lamps mounted on the equip‐ ment and shall be permitted to have terminals for remote lamps
    4. A relaying device arranged to energize the lamps auto‐ matically upon failure of the supply to the unit equip‐ mentThe batteries shall be of suitable rating and capacity to supply and maintain the total lamp load associated with the unit for not less than (a) or (b):
      1. For a period of 11∕2 hours, without the voltage falling below 871∕2 percent of normal voltage
      2. The unit equipment shall supply and maintain not less than 60 percent of the initial emergency illumination for a period of at least 11∕2 hours.

Unit equipment shall be permanently fixed in place (i.e., not portable) and shall have all wiring to each unit installed in accordance with the requirements of any of the wiring methods in Chapter 3. Flexible cord-and-plug connection shall be permitted, provided that the cord does not exceed 900 mm (3 ft) in length. The branch circuit feeding the unit equipment shall be the same branch circuit as that serving the normal lighting in the area and connected ahead of any local switches. Legally required standby luminaires that obtain power from a unit equipment and are not part of the unit equipment shall be wired to the unit equipment by one of the wiring methods of Chapter 3.

Exception: In a separate and uninterrupted area supplied by a mini‐ mum of three normal lighting circuits, a separate branch circuit for unit equipment shall be permitted if it originates from the same panel‐ board as that of the normal lighting circuits and is provided with a lock-on feature.

Part IV. Overcurrent Protection

  1. Accessibility. The branch-circuit overcurrent devices in legally required standby circuits shall be accessible to author‐ ized persons only.
  2. Ground-Fault Protection of Equipment. The alternate source for legally required standby systems shall not be required to provide ground-fault protection of equipment with automatic disconnecting means. Ground-fault indication at the legally required standby source shall be provided in accordance with 701.6(D) if ground-fault protection of equipment with automatic disconnecting means is not provided.
  3. Selective Coordination. Legally required standby system(s) overcurrent devices shall be selectively coordinated with all supply-side overcurrent protective devices.

Selective coordination shall be selected by a licensed profes‐ sional engineer or other qualified persons engaged primarily in the design, installation, or maintenance of electrical systems. The selection shall be documented and made available to those authorized to design, install, inspect, maintain, and operate the system.

Exception: Selective coordination shall not be required between two over‐ current devices located in series if no loads are connected in parallel with the downstream device.

Last posts

Sidebar