Symbols
Symbols vary slightly from industry to industry, and widely from drawing type to drawing type, at least here in the states. For example, for Process and Instrumentation Diagrams (generally the first drawing created in the process controls industry) the symbols established by the Instrument Society of America (ISA) (ISA-S5.1) are generally used, although in some industries the letter designations vary slightly. For panel wiring the symbols developed by the JIC (Joint Industry Conference) for switches, relays, etc. are used, but in Europe the symbols for many items vary slightly. For power and distribution (for example MCCs and switchgear) a whole different set of symbols are used for switches, transformers, etc. If pneumatic controls are part of the system, the National Fluid Power Association has a whole set of symbols that are used, but they are different than the ones used on the P&I Diagram! When it comes to the physical panel layout, here in the states we use third angle projection with the top view above the object, but in most of the world they use first angle projection with the top view below the object.
Confused? You should be, because it is in many ways a mess. However, history creates strange artifacts, and that is what is going on here.
What I suggest you do, after a tall cold beer and surfing the web per the above suggestion, is to get a good set of "similar too" drawings. These will be a clean looking set of drawings from a past project created by someone you respect. Use these as the guideline for symbols, nomenclature, and format. Drawing symbols and technique don't have to "right", they just have to be consistent. If you use symbols that are per national standards but aren't familiar to your local contractor you will have problems. If you use symbols normal for your area you will communicate your design intent clearly. And, after all, clear and precise communication is the objective of creating the drawing in the first place!