Basics of Electricity

This chapter introduces simple electrical circuits and common devices used to provide and control electrical power in heating, ventilation, and air conditioning (HVAC) systems. As all HVAC control systems will have relays, transformers, starters, and other electrical devices have electric systems in them it is necessary to understand the basic of electric circuits and systems. In a simple electrical circuit battery creates an electrical potential, called an electromotive force or voltage. The wires connect the battery to the device called the load, which has a resistance to electrical flow. When the switch is closed also called relay, an electrical circuit is formed direct current (dc) starts flowing. The electrical systems serving our homes and buildings are alternating current (ac) systems. Alternating current is produced by varying the electrical potential in a sinusoidal fashion. Further a power transformer is a device that is used primarily to convert one ac voltage to another. Based on the principle that alternating current in an inductor electromagnetically induces an electrical potential in adjacent conductors, transformers can interconnect two circuits without any electrical connection between them. Relays are used to implement control sequences using Boolean logic. Boolean logic is a way of making decisions using two-position switches or states. A switch may be opened or closed, also expressed as On or Off, 1 or 0. Many control systems are composed almost entirely of relays, so it is important to understand relay logic and how to read ladder diagrams of electrical devices.