At which reference new single line diagram of electrical system is made?

usualy there are many standert the desgine enginner need to know to make the document . so one-line diagrams, use graphic symbols in accordance with IEEE and. ANSI standards

check for std related to:

Graphic Symbols for Electrical and Electronic Diagrams. 

Electrical and Electronics Diagram

such as :

C42.100-1992 

100-1977 

Y32.2-1975

 315-1975 

Y14.15-1966 (R1973) 

the signal line diagram is the vital road map for all future testing ,service and maintenance activities. reference new single line diagram is to  switchgear