LD: leakage monitoring module (leakage switch).
RD: weak wiring box (information wiring box).
Common markers also include: QS knife switch, FU fuse, KM contactor, KA intermediate relay, KT time relay, KS speed relay, FR thermal relay, SB button, SQ travel switch.
Expanded
Drawing the general rules of the electrical schematic
Drawing the main circuit: drawing the main circuit, should be based on the provisions of the electrical graphic symbols with a thick solid line drawing out the main control and protection of the electrical equipment, such as circuit breakers, fuses, frequency converters, thermal relays, motors, etc., and in turn marked with the relevant text symbols.
Drawing a simple control circuit: for simple control circuits, as long as the main circuit based on the function to be achieved, combined with the requirements of the production process and the first and second order of the action of the equipment in order to analyze, carefully drawn.
Drawing complex control circuits: for complex control circuits, according to the functions accomplished by each part, divided into a number of local control circuits, and then compared with typical circuits, to find out the similarities, in line with the principle of the first simple and then complex, easy and then difficult to draw each local link, and then find the interrelationships of the links.
References
Baidu Encyclopedia - Electrical Schematic Diagrams