Switchesįigure 3 shows the most common types of switches and their symbols. The current flow for a transformer using the dot symbology is illustrated in Figure 2. If at a given instant the current is flowing into the transformer at the dotted end of the primary coil, it will be flowing out of the transformer at the dotted end of the secondary coil. On the primary side of the transformer the dot indicates current in on the secondary side the dot indicates current out. The marks usually appear as dots on a transformer symbol, as shown in Figure 2. This information can be used to determine the phase relationship (polarity) between the input and output terminals of a transformer. In addition to the transformer symbol itself, polarity marks are sometimes used to indicate current flow in the circuit. Figure 1 (B) shows how the basic symbol for the transformer is modified to represent specific types and transformer applications. The basic symbols for the various types of transformers are shown in Figure 1 (A). The information that follows provides details on the basic symbols used to represent components in electrical transmission, switching, control, and protection diagrams and schematics.įigure 1 Basic Transformer Symbols Transformers Once mastered, this knowledge should enable the reader to successfully understand most electrical diagrams and schematics. This chapter discusses the common symbols used to depict the many components in electrical systems. To read and interpret electrical diagrams and schematics, the reader must first be well versed in what the many symbols represent. This article concentrates on how electrical components are represented on diagrams and schematics. To read and interpret electrical diagrams and schematics, the basic symbols and conventions used in the drawing must be understood.