One-Line Diagram Standardized Symbols Information
In the Australian world, we use AS 1102 Graphical Symbols for Electrotechnical Documentation, which is derived from IEC 60617 Graphical Symbols for Diagrams.


  The following areas are covered in the database:
  
  
  Conductors and connecting devices
  Basic passive components
  Semiconductors and electron tubes
  Production and conversion of electrical energy (Includes generators and transformers)
  Switchgear, controlgear and protective devices (Includes all kinds of switches, circuit breakers, disconnectors, and so forth)
  Measuring instruments, lamps and signalling devices
  Telecommunications transmission, switching and peripheral equipment
  Architectural and topographical installation plans and diagrams
  Binary logic elements
  Analogue and hybrid elements
  


This set of standards would apply in the IEC-speaking world, i.e. Europe, the UK and Commonwealth, etc. I couldn't say what standard is used by our American cousins.