Introduction

To provide electrical service to a building or buildings, you must first determine what type of system is available from the utility company, or from a privately owned and operated system, such as might be found on a college or university campus, industrial or commercial complex, as the case may be. Once this is known, it is important to understand the characteristics of the system-not only voltage, capacity, and available fault current, but the operational, reliability, and relative cost characteristics inherent in the system by virtue of its configuration or arrangement. Knowing the characteristics associated with the system arrangement, the most appropriate service and distribution system for the application at hand can be determined.

Figures 3.1 through 3.10 feature the most frequently encountered system configurations and associated key characteristics attributable to their arrangement.

Figure 3.1: Radial circuit arrangements in commercial buildings. (Adapted from IEEE Std. 241-1990. Copyright 1990 IEEE. All rights reserved.)

Figure 3.10: Basic spot network. (Adapted from IEEE Std. 241-1990. Copyright 1990 IEEE. All rights reserved.)

Figure 3.2: Radial circuit arrangement-common primary feeder to secondary unit substations. (Adapted from IEEE Std. 241-1990. Copyright 1990 IEEE. All rights reserved.)

Figure 3.3: Radial circuit arrangement-individual primary feeders to secondary unit substations. (Adapted from IEEE Std. 241-1990. Copyright 1990 IEEE. All rights reserved.)

Figure 3.4: Primary radial-selective arrangements. (Adapted from IEEE Std. 241-1990. Copyright 1990 IEEE. All rights reserved.)

Figure 3.5: Seeondary-selective circuit arrangement (double-ended substation...