ractice for Electric Power Systems in Commercial Buildings
Recognized as an American National Standard (ANSI)
IEEE Std 241-1990

(Revision of IEEE Std 241-1983)

IEEE Recommended Practice for Electric
Power Systems in Commercial Buildings

Sponsor

Power Systems Engineering Committee
of the
IEEE Industry Applications Society

Approved December 6, 1990

IEEE Standards Board

Approved May 17, 1991

American National Standards Institute

Abstract:

A guide and general reference on electrical design for commercial buildings is provided. It covers
load characteristics; voltage considerations; power sources and distribution apparatus; controllers;
services, vaults, and electrical equipment rooms; wiring systems; systems protection and coordination;
lighting; electric space conditioning; transportation; communication systems planning; facility automation;
expansion, modernization, and rehabilitation; special requirements by occupancy; and electrical energy
management. Although directed to the power oriented engineer with limited commercial building
experience, it can be an aid to all engineers responsible for the electrical design of commercial buildings.
This recommended practice is not intended to be a complete handbook; however, it can direct the engineer
to texts, periodicals, and references for commercial buildings and act as a guide through the myriad of
codes, standards, and practices published by the IEEE, other professional associations, and governmental
bodies.

Keywords:

Commercial buildings, electric power systems, load characteristics
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1. Introduction .........................................................................................................................................................1
1.1 Scope .......................................................................................................................................................... 1
1.2 Commercial Buildings ............................................................................................................................... 3
1.3 The Industry Applications Society (IAS)................................................................................................... 4
1.4 IEEE Publications ...................................................................................................................................... 5
1.5 Professional Registration ........................................................................................................................... 5
1.6 Codes and Standards .................................................................................................................................. 6
1.7 Handbooks ................................................................................................................................................. 8
1.8 Periodicals .................................................................................................................................................. 9
1.9 Manufacturers' Data ................................................................................................................................. 10
1.10 Safety ....................................................................................................................................................... 10
1.11 Maintenance ............................................................................................................................................. 11
1.12 Design Considerations ............................................................................................................................. 12
1.13 Estimating ................................................................................................................................................ 15
1.14 Contracts .................................................................................................................................................. 16
1.15 Building Access and Loading .................................................................................................................. 16
1.16 Contractor Performance ........................................................................................................................... 16
1.17 Environmental Considerations ................................................................................................................. 17
1.18 Technical Files ......................................................................................................................................... 17
1.19 Electronic Systems ................................................................................................................................... 18
1.20 Power Supply Disturbances ..................................................................................................................... 18
1.21 Definitions................................................................................................................................................ 19
1.22 References ................................................................................................................................................ 24
2. Load
Characteristics..........................................................................................................................................25
2.1 General Discussion .................................................................................................................................. 25
2.2 Load Characteristics................................................................................................................................. 31
2.3 Electromagnetic Hazards, Pollution, and Environmental Quality ........................................................... 40
2.4 Additions to Existing Systems ................................................................................................................. 41
2.5 Total Load Considerations ....................................................................................................................... 42
2.6 Example Ñ Sample Partial Load Calculation for an Office Building..................................................... 46
2.7 References ................................................................................................................................................ 49
3. Voltage
Considerations .....................................................................................................................................50
3.1 General Discussion .................................................................................................................................. 50
3.2 Voltage Control in Electric Power Systems............................................................................................. 54
3.3 Voltage Selection ..................................................................................................................................... 63
3.4 Voltage Ratings for Utilization Equipment ............................................................................................. 65
3.5 Effect of Voltage Variation on Utilization Equipment ............................................................................ 66
3.6 Calculation of Voltage Drops .................................................................................................................. 70
3.7 Improvement of Voltage Conditions........................................................................................................ 82
3.8 Voltage-Drop Considerations in Locating the Low-Voltage Power Source............................................ 83
3.9 Momentary Voltage Variations Ñ Voltage Dips..................................................................................... 83
3.10 Calculation of Voltage Dips..................................................................................................................... 85
3.11 Phase Voltage Unbalance in Three-Phase Systems ................................................................................. 87
3.12 Harmonic Voltages .................................................................................................................................. 91
3.13 Transient Overvoltages ............................................................................................................................ 93
3.14 References ................................................................................................................................................ 94
3.15 Bibliography............................................................................................................................................. 95
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4.
Power Sources and Distribution Systems .........................................................................................................95
4.1 General Discussion .................................................................................................................................. 95
4.2 Electric Power Supply.............................................................................................................................. 95
4.3 Interrelated Utility and Project Factors That Influence Design ............................................................. 101
4.4 Electric Utility Metering and Billing ..................................................................................................... 102
4.5 Transformer Connections.............................................................