modulation cycle starts, a fraction of the total energy within each cycle is present at the output. "Boosting" by derating To achieve a "boost"-like effect, the PFC designs must be derated such that the maximum present at the input is higher than the nominal output requirements. When the supply is first turned on or operating under nominal conditions, the controller will continually be delivering less than 100% of its input. When a boost is required, the controller delivers a percentage closer to 100% of the maximum input available. Derating of mains powered, phase-fired controllers is important as they are often used to control resistive loads, such as heating elements. Over time, the resistance of heating elements can increase. To account for this, a phase-fired control must be able to provide some degree of extra voltage to draw the same heating current through the element. The only way of achieving this is to purposely design the supply to require less than 100% of the input's modulation cycle when the elements are first put in place, progressively opening the supply up towards delivering 100% of the input modulation cycle as the elements age. Applications The most common application is in dimmer switches for domestic lighting control. For industrial applications previously, extremely expensive and heavy multi-tapped transformers were used as the supplies for such elements, with the corresponding winding tap being connected to the element to produce the desired temperature. This limited the temperature resolution to the number of tap combinations available. They often find their way into controllers designed for equipment such as electric ovens and furnaces. In modern, usually high power, equipment, the transformer is replaced with phase-fired controllers connecting the load directly to the mains, resulting in a substantially cheaper and lighter system. However, the method is usually limited to use in equipment that would be unrealistic without it. This is because the removal of the mains transformer means that the load has electrical continuity with the input. For industrial ovens and furnaces the input is often the national grid AC, which is itself electrically referenced to ground. With the controller's output referenced to ground, a user need only be in contact with earth and one of the output terminals to risk receiving an electrical shock. With many high-power items of equipment running from three-phase 415 V, high current inputs and having any enclosure or framework present earthed (grounded), this