Injection of electron cyclotron (EC) waves into the lower hybrid (LH) current-sustained plasma in WT-2 increases the efficiency and the ramp-up rate of the LH-driven current when the high-energy electrons that couple to the LH waves are EC-heated. On the contrary, the efficiency decreases and the current ramp-up rate becomes negative when the bulk electrons are EC-heated. This selective EC-heating of bulk electrons or high-energy electrons is achieved by changing the radial position of the EC resonance layer in the plasma column.