There are 5 predefined PLC styles provided with AutoCAD Electrical, numbered 1 through 5. If one or more of these do not appeal to you or if you have a client with specific requirements not met by any of the 5 styles, you can pick one of the existing styles and modify it.
There are about 3 dozen symbols associated with each style. They are located in the library folder. They carry the file name "HP?*.dwg" where "?" is the style number.