Standby Power Systems

By Mike Holt, for EC&M Magazine

To apply the requirements of the National Electrical Code’s as it relates to Standby Power Systems we need to understand that there are three different types of systems recognized by the NEC. They include emergency, legally required, and optional standby systems; the requirements for emergency standby systems are contained in Article 700, legally required requirements are in 701, and Article 702 covers optional standby systems.

ARTICLE 700 – EMERGENCY SYSTEMS
The requirements of Article 700 apply only to the wiring methods for "emergency systems" that are essential for safety to human life and are required by federal, state, or municipal governments or other agencies having jurisdiction. When normal power is lost, emergency systems shall be able to supply standby power in 10 seconds or less.

ARTICLE 701 – LEGALLY REQUIRED STANDBY SYSTEMS
Legally required standby systems provide electric power to aid in firefighting, rescue operations, control of health hazards, and similar operations. When normal power is lost, legally required systems shall be able to supply standby power in 60 seconds or less, instead of the 10 seconds or less required of emergency systems.

ARTICLE 702 – OPTIONAL STANDBY SYSTEMS
Optional standby systems are intended to protect public or private facilities or property where life safety does not depend on the performance of the system. These 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 that, when stopped during any power outage, could cause discomfort, serious interruption of the process, damage to the product or process. Optional standby systems are intended to supply on-site generated power to selected loads either automatically or manually.

Article 700 -- Emergency Systems

I. General

700.1. Scope
Article 700 is intended to apply to the installation, operation, and maintenance of emergency systems consisting of circuits and equipment intended to supply, distribute, and control electricity for illumination or power, or both, to required facilities when the normal electrical supply or system is interrupted. Figure 700.01.

Mike Holt’s Comment: Graphics are not contained in this newsletter.

Emergency systems are those systems legally required and classed as emergency by municipal, state, federal, or other Codes, or by a governmental agency having jurisdiction. These systems are intended to automatically supply illumination or power essential for safety to human life. The requirements of Article 700 apply only to the wiring methods for "emergency systems" that are essential for safety to human life and are required by federal, state, or municipal governments or other agencies having jurisdiction. When normal power is lost, emergency systems shall be able to supply standby power in 10 seconds or less.

FPN No. 3: Emergency systems are generally installed where artificial illumination is required for safe exiting and for panic control in buildings subject to occupancy by large numbers of persons, such as hotels, theaters, sports arenas, health care facilities, and similar institutions. Emergency systems may also provide power to maintain life, fire detection and alarm systems, elevators, fire pumps, public safety communications systems, industrial processes where current interruption would produce serious life safety or health hazards, and similar functions.

FPN No. 4: For specific locations where emergency lighting is required for life safety, see Life Safety Code, NFPA 101.

700.2. Application of Other Articles
Except as modified by this article, all other requirements contained in Chapter 1 through 4 of the NEC shall apply.

700.3. Equipment Approval
All equipment shall be approved for the intended use in accordance with 90.4 and 100.2.

700.4. Tests and Maintenance
Emergency system testing consists of acceptance testing and operational testing. This section requires both types of testing, and written records of both types of testing and maintenance shall be maintained [700.4(D)].

(A) Conduct or Witness Test. To ensure that the emergency system meets or exceeds the original installation specification, the AHJ shall conduct or witness an acceptance test of the complete emergency system before the system is used. A written record is required, see 700.4(D).

(B) Tested Periodically. Systems shall be operational tested periodically on a schedule acceptable during the life of the system by to the AHJ to ensure the systems are maintained in proper operating condition. The purpose of the text is to ensure that the emergency system remains functional and that adequate maintenance has been performed, see 700.4(E). A written record is required, see 700.4(D).

Author’s Comment: Running the emergency system to power the loads of the facility is considered an acceptable method of operational testing.

(C) Battery Systems Maintenance. Where battery batteries are used for starting, control, or ignition in auxiliary engines, the AHJ shall require periodic maintenance.

(D) Written Record. A written record shall be kept of such tests and maintenance.

(E) Testing Under Load. Means for testing all emergency lighting and power systems during maximum anticipated load conditions shall be provided.

Author’s Comment: For further information on test and maintenance see NFPA 72, National Fire Alarm Code; NFPA 99, Standard For Health Care Facilities; NFPA 101, Life Safety Code; NFPA 110, Standard For Emergency And Standby Power Systems; And NFPA 111, Standard On Stored Electrical Energy Emergency And Standby Power Systems.

700.5. Capacity
(A) Capacity and Rating. An emergency system shall have adequate capacity to safely carry all of loads that are expected to operate simultaneously on the emergency system. In addition, the emergency system shall be sized to restart emergency loads, such as motors, that may have stopped.

Equipment for the emergency system shall have suitable capacity to handle the maximum available fault current at its terminals. The use of current limiting devices (often fuses) in accordance with manufacturer’s instructions is one way of insuring the equipment is capable of handling the available fault.

Author’s Comment: See 110.9, 110.10, and 240.2, and 240.60 for other NEC requirements relating to the issue of available fault and current limiting devices.

(B) Selective Load Pickup, Load Shedding, and Peak Load Shaving. The alternate power source (generator, UPS, etc.) can supply emergency, legally required standby and optional standby system loads, where automatic selective load pickup and load shedding is provided as needed to ensure adequate power for:
the emergency circuits,
the legally required standby circuits, and
the optional standby circuits, in that order of priority.
The alternate power source can be used for peak load shaving, provided the above conditions are met.

Author’s Comment: Using the alternate power source for peak load shaving operation can be used to satisfy the test requirement of 700.4(B), provided all of the requirements of 700.4 are met. The use of the emergency generator to supply nonemergency loads ensures that the emergency generator will supply emergency power when it is needed.

A portable or temporary alternate source shall be available whenever the emergency generator is out of service for major maintenance or repair. According to the NEC Handbook, a major maintenance or repair procedure is one that keeps the generator set out of service for more than a few hours.

700.6. Transfer Equipment
(A) General. Transfer equipment, including automatic transfer switches, shall be automatic, identified for emergency use, and approved by the AHJ. Transfer equipment shall be designed and installed to prevent the inadvertent interconnection of normal and emergency sources of supply in any operation of the transfer equipment.

(B) Bypass Isolation Switches. Means can bypass and isolate the transfer equipment.

(C) Automatic Transfer Switches. Automatic transfer switches shall be electrically operated and mechanically held.

(D) Use. Transfer equipment shall supply only emergency loads. Other loads shall not be supplied from the emergency system transfer switch. Figure 700.06d.

Author’s Comment: A generator can supply emergency loads as well as other loads, but the transfer switch for the emergency system is only permitted to supply emergency loads. Multiple transfer switches are required where a single generator is used to supply emergency and other loads.

700.7. Signals
Audible and visual signal devices shall be provided, where practicable, for the following purposes.

(A) Derangement. To indicate derangement of the emergency source.

Author’s Comment: According to Webster’s Dictionary, derangement means to make insane!

(B) Carrying Load. To indicate that the battery is carrying load.

(C) Not Functioning. To indicate that the battery charger is not functioning.

Author’s Comment: To minimize emergency equipment failure, signal devices (audio and visual) shall be installed to annunciate trouble.

(D) Ground Fault. To indicate a ground fault in solidly grounded wye emergency systems of more than 150V to ground and circuit-protective devices rated 1000A or more. The sensor for the ground-fault signal devices shall be located at, or ahead of, the main system disconnecting means for the emergency source, and the maximum setting of the signal devices shall be for a ground-fault current of 1200As. Instructions on the course of action to be taken in event of indicated ground fault shall be located at or near the sensor location.

700.8. Signs
(A) Emergency Sources. A sign shall be placed at the service entrance equipment indicating type and location of on-site emergency power sources.

Exception: A sign shall not be required for individual unit equipment as specified in 700.12(E).

II. Circuit Wiring

700.9. Wiring, Emergency System
(A) Identification. All boxes and enclosures (including transfer switches, generators, and power panels) for emergency circuits shall be permanently marked so they will be readily identified as a component of an emergency circuit or system. Figure 700.09a.

(B) Wiring. To ensure that any fault on the normal wiring circuits will not affect the performance of the emergency wiring or equipment, wiring from an emergency source shall be kept entirely independent of all other wiring, except as permitted for:
(1) Wiring in transfer equipment enclosures.
(2) Luminaires supplied from two sources.
(3) Common junction box attached to luminaires supplied from two sources.
(4) Common junction box attached to unit equipment (battery packs).

Wiring of two or more emergency circuits supplied from the same source shall be permitted in the same raceway, cable, box, or cabinet.

(C) Wiring Design and Location. Emergency wiring circuits shall be designed and located to minimize the hazards that might cause failure due to flooding, fire, icing, vandalism, and other adverse conditions.

Author’s Comment: This requirement also applies to 700.12 power sources.

III. Sources of Power

700.12. General Requirements
In the event of failure of the normal supply to, emergency power shall be available within 10 seconds. The supply system for emergency purposes can be any of the following to satisfy this requirement.

Equipment shall be designed and located to minimize the hazards that might cause complete failure due to flooding, fires, icing, and vandalism.

(A) Storage Battery. Storage batteries used as a source of power for emergency systems shall be of suitable rating and capacity to supply and maintain the total load for a period of 1 1/2 hours minimum, without the voltage applied to the load falling below 87 1/2 percent of normal.

(B) Generator Set.
(1) Prime Mover-Driven. A generator set driven by a prime mover acceptable to the AHJ sized in accordance with 700.5. Means shall be provided for automatically starting the prime mover on failure of the normal service and for automatic transfer and operation of all required electrical circuits in accordance with 700.6. Figure 700.12b.

(2) Internal Combustion as Prime Movers. Where internal combustion engines are used as the prime mover, an on-site fuel supply shall be provided with an on-premise fuel supply sufficient for not less than 2 hours full-demand operation of the system.

(6) Disconnect. Where an outdoor-housed generator for emergency circuits is equipped with a readily accessible disconnecting means located within sight (within 50 ft) of the building or structure supplied, an additional disconnecting means is not required on or at the building or structure for the generator feeder conductors. Figure 700–1

Author’s Comment: See Article 100 for the definition of “in sight.”

(C) Uninterruptible Power Supplies. Uninterruptible power supplies used to provide power for emergency systems shall comply with the applicable provisions of 700.12(A) and (B).

(D) Separate Service. A second service where acceptable to the AHJ. This service shall be in accordance with Article 230, with separate service drop or lateral, widely separated electrically and physically from the normal service to minimize the possibility of simultaneous interruption of supply. Figure 700.12d 01.

Author’s Comment: Tapping ahead of the normal service equipment to provide power for the emergency system in not permitted by the NEC. Figure 700.12d 02.

(E) Unit Equipment. Individual unit equipment (battery pack) for emergency illumination shall consist of the following. Figure 700.12e:
(1) A rechargeable battery
(2) A battery charging means
(3) Provisions for one or more lamps mounted on the equipment, or can have terminals for remote lamps, or both, and
(4) A relaying device arranged to energize the lamps automatically upon failure of the supply to the unit equipment.

Unit equipment shall be permanently fixed in place. Flexible cord and plug connection shall be permitted, provided that the cord does not exceed 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, but it shall connected ahead of any local switches. The branch circuit that feeds the unit equipment shall be clearly identified at the distribution panel.

IV. Emergency System Circuits for Lighting and Power

700.15. Loads on Emergency Branch Circuits
No loads, other than those required for emergency use, shall be supplied by emergency lighting circuits.

700.16. Emergency 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 light bulb, will not leave in total darkness any space that requires emergency illumination.

V. Control — Emergency Lighting Circuits

700.20. Switch Requirements
The switches installed in emergency lighting circuits shall be arranged so that only authorized persons will have control of emergency lighting.

Switches connected in series or 3- and 4-way switches shall not be used.

700.21. Switch Location
All manual switches for controlling emergency circuits shall be in locations convenient to authorized persons responsible for their actuation.

VI. Overcurrent Protection

700.25. Accessibility
The branch-circuit overcurrent protection devices in emergency circuits shall be accessible to authorized persons only.

700.26. Ground-Fault Protection of Equipment
The alternate source for emergency systems shall not be required to have ground-fault protection of equipment and ground-fault indication of the emergency source shall be provided in accordance with 700.7(D).

Article 701 -- Legally Required Standby

I. General

701.1. Scope
The provisions of this article apply to the electrical safety of the installation, operation, and maintenance of legally required standby systems consisting of circuits and equipment intended to supply, distribute, and control electricity to required facilities for illumination or power, or both, when the normal electrical supply or system is interrupted.

Legally required standby systems provide electric power to aid in firefighting, rescue operations, control of health hazards, and similar operations. When normal power is lost, legally required systems shall be able to supply standby power in 60 seconds or less, instead of the 10 seconds or less required of emergency systems.

Author’s Comment: The requirements for legally required standby systems are very similar to those for emergency systems, Article 700. For example, wiring for emergency systems is required to be kept entirely independent of other wiring, but this is not the case for legally required standby systems.

The requirements contained in this article only apply to the wiring of permanently legally required standby systems, including the power source.

701.2. Legally Required Standby Systems
Legally required standby systems are those systems classed as legally required standby by municipal, state, federal, 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.

FPN: Legally required standby systems typically supply loads, such as heating and refrigeration systems, communications systems, ventilation and smoke removal systems, and industrial processes, that, when stopped could create hazards or hamper rescue or fire-fighting operations.

701.3. Application of Other Articles
Except as modified by this article, all other requirements contained in Chapter 1 through 4 of the NEC shall apply.

701.4. Equipment Approval
All equipment shall be approved for the intended use in accordance with 90.4 and 100.2.

701.5. Tests and Maintenance for Legally Required Standby Systems
Legally required system testing consists of acceptance testing and operational testing. This section requires both types of testing as well as written records of both types of testing and maintenance.

(A) Conduct or Witness Test. To ensure that the emergency system meets or exceeds the original installation specification, the AHJ shall conduct or witness an acceptance test of the complete emergency system before the system is used. A written record is required, see 701.5(D).

(B) Tested Periodically. Systems shall be operational tested periodically on a schedule acceptable during the life of the system by to the AHJ to ensure the systems are maintained in proper operating condition. The purpose of the text is to ensure that the emergency system remains functional and that adequate maintenance has been performed, see 701.5(E). A written record is required, see 701.5(D).

Author’s Comment: Running the emergency system to power the loads of the facility is considered an acceptable method of operational testing.

(C) Battery Systems Maintenance. Where battery batteries are used for starting, control, or ignition in auxiliary engines, the AHJ shall require periodic maintenance.

(D) Written Record. A written record shall be kept of such tests and maintenance.

(E) Testing Under Load. Means for testing all legally required power systems during maximum anticipated load conditions shall be provided.

701.6. Capacity and Rating
A legally required standby system shall have adequate capacity to safely carry all of loads that are expected to operate simultaneously on the system.

Legally required standby system equipment shall be suitable for the maximum available fault current at its terminals.

The alternate power source can supply legally required standby and optional standby system loads where automatic selective load pickup and load shedding is provided as needed to ensure adequate power to the legally required standby circuits.

701.7. Transfer Equipment
(A) General. Transfer equipment, including automatic transfer switches, shall be automatic, identified for emergency use, and approved by the AHJ. Transfer equipment shall be designed and installed to prevent the inadvertent interconnection of normal and emergency sources of supply in any operation of the transfer equipment.

(B) Bypass Isolation Switches. Means can bypass and isolate the transfer equipment.

(C) Automatic Transfer Switches. Automatic transfer switches shall be electrically operated and mechanically held.

(D) Use. Transfer equipment shall supply only emergency loads. Other loads shall not be supplied from the emergency system transfer switch. Figure 700.06d.

Author’s Comment: A generator can supply emergency loads as well as other loads, but the transfer switch for the emergency system is only permitted to supply emergency loads. Multiple transfer switches are required where a single generator is used to supply emergency and other loads.

701.8. Signals
Audible and visual signal devices shall be provided, where practicable, for the following purposes.

(A) Derangement. To indicate derangement of the standby source.

Author’s Comment: According to Webster’s Dictionary, derangement means to make insane!

(B) Carrying Load. To indicate that the standby source is carrying load.

(C) Not Functioning. To indicate that the battery charger is not functioning.

Author’s Comment: To minimize emergency equipment failure, signal devices (audio and visual) shall be installed to annunciate trouble.

701.9. Signs
(A) Mandated Standby. A sign shall be placed at the service entrance equipment indicating type and location of on-site legally required standby power sources.

II. Circuit Wiring

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

III. Sources of Power

701.11. Legally Required Standby Systems
In the event of failure of the normal supply to, emergency power shall be available within 60 seconds. The supply system for emergency purposes can be any of the following to satisfy this requirement.

(A) Storage Battery. Storage batteries 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 a period of 1 1/2 hours minimum, without the voltage applied to the load falling below 87 1/2 percent of normal.

(B) Generator Set.
(1) Prime Mover-Driven. A generator set driven by a prime mover acceptable to the AHJ sized in accordance with 701.6. Means shall be provided for automatically starting the prime mover on failure of the normal service and for automatic transfer and operation of all required electrical circuits in accordance with 700.6. Figure 700.12b.

(2) Internal Combustion as Prime Movers. Where internal combustion engines are used as the prime mover, an on-site fuel supply shall be provided with an on-premise fuel supply sufficient for not less than 2 hours full-demand operation of the system.

(5) Disconnect. Where an outdoor-housed generator for legally required circuits is equipped with a readily accessible disconnecting means located within sight (within 50 ft) of the building or structure supplied, an additional disconnecting means is not required on or at the building or structure for the generator feeder conductors.

(C) Uninterruptible Power Supplies. Uninterruptible power supplies used to provide power for legally required standby systems shall comply with the applicable provisions of 701.11(A) and (B).

(D) Separate Service. A second service shall be permitted where acceptable to the AHJ. This service shall be in accordance with Article 230, with separate service drop or lateral, widely separated electrically and physically from the normal service to minimize the possibility of simultaneous interruption of supply. Figure 701-11d.

(E) Connection Ahead of Service Disconnecting Means.
Where acceptable to the AHJ, connections located ahead, but not within the same cabinet, enclosure, or vertical switchboard section as the service disconnecting means is permitted.

The standby service disconnect shall be sufficiently separated from the normal service disconnection means to prevent simultaneous interruption of supply through an occurrence with the building or groups of buildings served. Figure 701–1

FPN: See 230.82 for equipment permitted on the supply side of a service disconnecting means.

(F) Unit Equipment. Individual unit equipment (battery pack) for legally required illumination shall consist of the following. Figure 701.11e:
(1) A rechargeable battery
(2) A battery charging means
(3) Provisions for one or more lamps mounted on the equipment, or can have terminals for remote lamps, or both, and
(4) A relaying device arranged to energize the lamps automatically upon failure of the supply to the unit equipment.

Unit equipment shall be permanently fixed in place. Flexible cord and plug connection shall be permitted, provided that the cord does not exceed 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, but it shall connected ahead of any local switches. The branch circuit that feeds the unit equipment shall be clearly identified at the distribution panel.

IV. Overcurrent Protection

701.15. Accessibility
The branch-circuit overcurrent protection devices in legally required standby circuits shall be accessible to authorized persons only.

701.17. Ground-Fault Protection of Equipment
The alternate source for legally required standby systems shall not be required to have ground-fault protection of equipment.

Article 702 -- Optional Standby Systems

I. General

702.1. Scope
The systems covered by this Article consist of those that are permanently installed, including prime movers, and those that are arranged for a connection to a premises wiring system from a portable alternate power supply. Figure 702–1

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

FPN: 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 process, damage to the product or process, or the like.

702.3. Application of Other Articles
Except as modified by this article, all other requirements contained in Chapter 1 through 4 of the NEC shall apply.

702.4. Equipment Approval
All equipment shall be approved for the intended use in accordance with 90.4 and 100.2.

702.5. Capacity and Rating
An optional standby system shall have adequate capacity to safely carry all of loads that are expected to operate simultaneously.

Equipment shall have suitable capacity to handle the maximum available fault current at its terminals.

The user of the optional standby system can select the load connected to the system.

702.6 Transfer Equipment
A transfer switch is required for all fixed or portable optional standby power systems.

702.7. Signals
Audible and visual signal devices shall be provided, where practicable, for the following purposes.
(1) Derangement. To indicate derangement of the optional standby system.

Author’s Comment: According to Webster’s Dictionary, derangement means to make insane!

(2) Carrying Load. To indicate that the optional standby source is carrying load.

702.8. Signs
(A) Emergency Sources. A sign shall be placed at the service entrance equipment indicating type and location of on-site emergency power sources.

II. Circuit Wiring

702.9. Wiring Optional Standby Systems
The optional standby system wiring can occupy the same raceways, cables, boxes, and cabinets with other general wiring.


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