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Article 702

Optional Standby Systems

Part I. General

  1. Scope. The provisions of this article apply to the instal‐ lation and operation of optional standby systems.The systems covered by this article consist of those that are permanently installed in their entirety, including prime
  2. ARTICLE 702 — OPTIONAL STANDBY SYSTEMS

movers, and those that are arranged for a connection to a premises wiring system from a portable alternate power supply.

702.2 Definition.

Optional Standby Systems. Those systems intended to supply power to public or private facilities or property where life safety does not depend on the performance of the system. These systems are intended to supply on-site generated power to selected loads either automatically or manually.

Informational Note: Optional standby systems are typically installed to provide an alternate source of electric power for such facilities as industrial and commercial buildings, farms, and residences and to serve loads such as heating and refrigeration systems, data processing and communications systems, and industrial processes that, when stopped during any power outage, could cause discomfort, serious interruption of the proc‐ ess, damage to the product or process, or the like.

  1. Capacity and Rating.
    1. Available Short-Circuit Current. Optional standby system equipment shall be suitable for the maximum available short- circuit current at its terminals.
    2. System Capacity. The calculations of load on the standby source shall be made in accordance with Article 220 or by another approved method.
      1. Manual Transfer Equipment. Where manual transfer equipment is used, an optional standby system shall have adequate capacity and rating for the supply of all equipment intended to be operated at one time. The user of the optional standby system shall be permitted to select the load connected to the system.
      2. Automatic Transfer Equipment. Where automatic transfer equipment is used, an optional standby system shall comply with (2)(a) or (2)(b).
        1. Full Load. The standby source shall be capable of supplying the full load that is transferred by the automatic transfer equipment.
        2. Load Management. Where a system is employed that will automatically manage the connected load, the standby source shall have a capacity sufficient to supply the maximum load that will be connected by the load management system.
  2. Transfer Equipment. Transfer equipment shall be suita‐ ble for the intended use and designed and installed so as to prevent the inadvertent interconnection of normal and alter‐ nate sources of supply in any operation of the transfer equip‐ ment. Transfer equipment and electric power production systems installed to permit operation in parallel with the normal source shall meet the requirements of Article 705.Transfer equipment, located on the load side of branch circuit protection, shall be permitted to contain supplemental overcurrent protection having an interrupting rating sufficient for the available fault current that the generator can deliver. The supplementary overcurrent protection devices shall be part of a listed transfer equipment.Transfer equipment shall be required for all standby systems subject to the provisions of this article and for which an electric utility supply is either the normal or standby source.Exception: Temporary connection of a portable generator without trans‐ fer equipment shall be permitted where conditions of maintenance and supervision ensure that only qualified persons service the installationand where the normal supply is physically isolated by a lockable discon‐ necting means or by disconnection of the normal supply conductors.The short-circuit current rating of the transfer equipment, based on the specific overcurrent protective device type and settings protecting the transfer equipment, shall be field marked on the exterior of the transfer equipment.
  3. Signals. Audible and visual signal devices shall be provi‐ ded, where practicable, for the following purposes specified in 702.6(A) and (B).
    1. Malfunction. To indicate malfunction of the optional standby source.
    2. Carrying Load. To indicate that the optional standby source is carrying load.
    Exception: Signals shall not be required for portable standby power sources.
  4. Signs.
  1. Standby. A sign shall be placed at the service-entrance equipment that indicates the type and location of each on-site optional standby power source. A sign shall not be required for individual unit equipment for standby illumination.
  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:WARNINGSHOCK 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).
  3. Power Inlet. Where a power inlet is used for a temporary connection to a portable generator, a warning sign shall be placed near the inlet to indicate the type of derived system that the system is capable of based on the wiring of the transfer equipment. The sign shall display one of the following warn‐ ings:

WARNING:

FOR CONNECTION OF A SEPARATELY DERIVED (BONDED NEUTRAL) SYSTEM ONLY

or WARNING:

FOR CONNECTION OF A NONSEPARATELY DERIVED (FLOATING NEUTRAL) SYSTEM ONLY

Part II. Wiring

  1. Wiring Optional Standby Systems. The optional standby system wiring shall be permitted to occupy the same raceways, cables, boxes, and cabinets with other general wiring.
  2. Portable Generator Grounding.
    1. Separately Derived System. Where a portable optional standby source is used as a separately derived system, it shall be grounded to a grounding electrode in accordance with 250.30.
    2. Nonseparately Derived System. Where a portable optional standby source is used as a nonseparately derived system, the equipment grounding conductor shall be bonded to the system grounding electrode.
  3. Outdoor Generator Sets.
  1. Portable Generators Greater Than 15 kW and Permanently Installed Generators. Where an outdoor housed generator set is equipped with a readily accessible disconnecting means in accordance with 445.18, and the disconnecting means is loca‐ ted within sight of the building or structure supplied, an addi‐ tional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure. Where the generator supply conductors terminate at a disconnecting means in or on a building or structure, the disconnecting means shall meet the requirements of 225.36.
  2. Portable Generators 15 kW or Less. Where a portable generator, rated 15 kW or less, is installed using a flanged inlet or other cord- and plug-type connection, a disconnecting means shall not be required where ungrounded conductors serve or pass through a building or structure.imageN
  3. Power Inlets Rated at 100 Amperes or Greater, for Porta‐ ble Generators. Equipment containing power inlets for the connection of a generator source shall be listed for the inten‐ ded use. Systems with power inlets shall be equipped with an interlocked disconnecting means.

Exception No. 1: If the inlet device is rated as a disconnecting means

Exception No. 2: Supervised industrial installations where permanent space is identified for the portable generator located within line of sight of the power inlets shall not be required to have interlocked disconnect‐ ing means nor inlets rated as disconnects.

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