Overview

Figure 2-1 shows the most common electrical system voltages for 60-hertz (Hz) systems, and Fig. 2-2 shows the most common electrical system voltages for 50-Hz systems. In general, 60-Hz systems are designed to be in compliance with Institute of Electrical and Electronics Engineers (IEEE)/American National Standards Institute (ANSI)/National Electrical Manufacturers Association (NEMA)/ National Electrical Code (NEC) requirements, whereas, generally, 50-Hz systems are designed to be in compliance with International Electrotechnical Commission (IEC) or Australian standards. This book concentrates on 60-Hz systems but notes 50-Hz system information where it is pertinent. The immediate question arises as to how to select the most correct voltage for a system that is being designed, and the answer is equally straightforward and is shown in the flowchart in Fig. 2-3. The ultimate goal of this flowchart is to provide the load with proper current and voltage but not to exceed approximately 2500 amperes (A) at any one bus because of switchgear construction physical constraints.