DOE-HDBK-1016/1-93
Electrical Diagrams and Schematics
ELECTRICAL DIAGRAMS AND SCHEMATICS
When a switch is used in a circuit, it may contain several sets of contacts or small switches
internal to it. The internal switches are shown individually on a schematic. In many cases, the
position of one internal switch will effect the position of another. Such switches are called
ganged switches and are symbolized by connecting them with a dashed line as shown in
Figure 15 (A). In that example, closing Switch 1 also closes Switch 2. The dashed line is also
used to indicate a mechanical interlock between two circuit components. Figure 15 (B) shows
two breakers with an interlock between them.
In system single line diagrams, transformers are often represented by the symbol for a single-
Figure 15 Ganged Switch Symbology
phase air core transformer; however, that does not necessarily mean that the transformer has an
air core or that it is single phase. Single line system diagrams are intended to convey only
general functional information, similar to the type of information presented on a P&ID for a
piping system. The reader must investigate further if more detail is required. In diagrams
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