Article 701 Legally Required Standby Systems

A. General



This article lays out the electrical safety requirements for the installation, operation, and maintenance of legally required standby power systems. This includes all equipment necessary to deliver power to the load. The reader is referred to NFPA 99-2002 (ANSI) Standard for Health Care Facilities for additional information, NFPA 110-2002 (ANSI) Emergency and Standby Power Systems for performance information, and to ANSI/IEEE 446-1995 Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications for further information.



These are systems that have this classification set by any governmental agency having jurisdiction. They are intended to supply power automatically to selected loads other than emergency system loads if the normal source fails. They differ from emergency systems in that they are not required for direct safety to life. They do supply power where the interruption might create a hazard or hamper rescue or firefighting operations. Some examples are given in the code to help the reader.


Application of Other Articles

Applicable articles of the Code apply unless otherwise modified in this Article.


Equipment Approval

Items must be approved for this use.


Test and Maintenance for Legally Required Standby Systems

(A) Conduct or Witness Test. When the installation is complete the authority having jurisdiction must either conduct or witness a test.

(B) Tested Periodically. To assure proper maintenance and operation the system must be tested on a schedule accepted by the authority having jurisdiction.

(C) Battery Systems Maintenance. Periodic maintenance is required if the batteries are used for control, starting, or ignition of a prime mover.

(D) Written Record. A written record must be kept of all tests and maintenance.

(E) Testing under Load. Provisions must be made for testing under load.


Capacity and Rating

The system must be able to supply the entire load operating together. It must also be able to withstand the available fault current.


Transfer Equipment

The transfer equipment must be automatic, identified for standby use, and approved by the authority having jurisdiction. Interconnection of the normal and emergency sources must be prevented. Bypass means for isolation of the transfer switch is permitted. Automatic transfer switches have to be electrically operated and mechanically held.



Audible and visual signals must be provided to indicate the derangement of the standby source, that the standby source is carrying the load, and that the battery charger is not functioning.



The type and location of the system must be indicated on a sign at the service entrance. There is an exception for certain unit equipment. If the system is grounded to a remote grounding electrode a sign must be placed at the grounding location identifying all emergency and normal sources connected there.

II. Circuit Wiring


Wiring Legally Required Standby Systems

The wiring for this system can occupy the raceways, cables, boxes, cabinets, etc. as the general wiring.

III. Sources of Power


Legally Required Standby Power Systems

The current must be available for use within 60 seconds of the loss of the normal power. The supply system can be any one of the following: storage battery, generator set, uninterruptible power supply, separate service, connection ahead of the service disconnecting means, fuel cell system, and unit equipment. Each is covered in the code in detail as to specific requirements. Again it must be noted that some of these may not be permitted for specific occupancies as noted in other documents (i.e., health care facilities).

VI. Overcurrent Protection




Ground-Fault Protection of Equipment

This is not required for the alternate source.



The system must be selectively coordinated with the supply side overcurrent protection devices.

Article 90 Introduction


Wiring and Protection

Wiring Methods and Materials

Equipment for General Use

Special Occupancies

Special Equipment

Special Conditions


Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

Annex D. Examples

Annex E. Types of Construction

Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120 © 2008-2020.
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