The low-cost reactive power electronic REQ/L models allow the delayed insertion of 4-8-12 capacitor banks, automatically with the changing of power factor, measured on the supply line, or manually by means of on board dip-switches. The presence of signal-leds allows a simple knowledge of the maneuvers and of the measures carried out from the relay. The insertion of the capacitor banks is made according to a logic that optimizes the number of maneuvers and does not stress the operating organs of the p.l.c. plant.