The 12C Series Powerstat variable transformers come in 240 Vac single- and three-phase, manually-operated, open-construction models designed for back-of-panel mounting. The transformers are rated 0.7A for constant current loads and 0.9A for constant impedance loads such as incandescent lamps. The tapping arrangement permits an output voltage of zero to line voltage or to 10% above line voltage to allow compensation for a drop in line voltage or to provide a wider working range. All 12C Series units are claimed to have improved thermal contact with the mounting base for cooler operation. They can be connected such that an increasing output voltage is controlled with either a clockwise or counterclockwise knob rotation. They require negligible maintenance and are designed for a long, trouble-free life. All are UL recognized for the USA and Canada and are priced from $93 to $406 depending on the model.