1.4 kW will pull about 5.8 amps at  240v so you are safe to put 5 maybe 6 on your circuit. How many outlets are you sharing on the circuit? To add more you would need to upgrade the panel to 200A then you could add 2 more 40A RCD's. Also I would spread the amps over multiple outlets because the wiring in one outlet is probably not sufficient to handle 40A.