There are several reasons to choose one voltage level over another for electrical transmission. Once the requirements for electrical transmission have been determined, the electrical engineer must design a system that is both safe and effective for the commercial building.

First, the requirements of the electrical system must be defined. Voltage is determined by the equipment requiring power. Another reason is the cost.

Low-voltage systems typically serve lighting, fire/life safety systems, receptacles, communication systems and small equipment. Medium-voltage systems serve many different needs in commercial buildings. ANSI C84.1 defines medium voltage as being “a class of nominal system voltages greater than 1,000 volts and less than 100 kilovolts.”

This will review both the application and design requirements for low- and medium-voltage electrical systems.

Learning objectives:

  • Know the codes and standards that define electrical system design, including NFPA 70: National Electrical Code.
  • Learn which products or systems typically fall into a low- or medium-voltage classification.
  • Understand the basics of a single-line diagram and the items included.
  • Review buildings in which both low- and medium-voltage electrical systems have been included and their application.