The LG terminal is a line filter ground terminal in the power supply module. It is intended for guiding any external noise produced in the power supply or switching noise in the power supply unit to the ground. The L and N of the power supply are connected via a capacitor and the power supply has a midpoint potential.
Meanwhile, FG is a frame ground terminal as a measure against noise of the internal circuit (5 V, 24 V, etc.). It is connected with 0 V of the SX bus.
Generally, connect the LG and FG terminals using the shorting bar supplied and provide D-type grounding (100? or lower) with a wire of at least 2 mm2.