10 °C reduction in motor temperature under voltage optimisation due to the reduced losses in the motor. Common power quality problems Overvoltage Overvoltage refers to voltage higher than the voltage at which equipment is designed to operate most effectively. It can cause a reduction in equipment lifetime and increases in energy consumed with no improvement in performance. A commentary on the Wiring Regulations BS 7671 makes the following statements in relation to overvoltage: "A 230 V rated lamp used at 240 will achieve only 55% of its rated life" (referring to incandescent lamps) and "A 230 V linear appliance used on a 240 V supply will take 4.3% more current and will consume almost 9% more energy". Various technologies can be used to avoid overvoltage, but it must be done so efficiently so that energy savings resulting from using the correct voltage are not offset by energy wasted within the device used to do so. Reliability is also important, and there are potential problems inherent in running full incoming power through electro-mechanical devices such as servo-controlled variable autotransformers. Undervoltage refers to voltage lower than the voltage at which equipment is designed to operate most effectively. If the design of the VO does not take into consideration voltage drop over distance to remote power users, then this may lead to premature equipment failure, failure to start up, increased temperature in the case of motor windings and loss of service. Harmonics Harmonics are current and voltage waveforms at multiples of the fundamental frequency of the 50 Hz (or 60 Hz) main supply. Harmonics are caused by non-linear loads, which include power supplies for computer equipment, variable speed drives, and discharge lighting. "Triplen" harmonics (odd multiples of the third harmonic) result when phase voltages are not balanced in a three phase power systems and add in the neutral, causing wasteful currents to flow. The possible effects if the level of harmonics, known as total harmonic distortion becomes too high include damage to sensitive electronic equipment and reduction in the efficiency of the HV transformer. The efficiency of electrical loads can be improved by attenuating harmonics at the supply, or by preventing their generation. Some voltage optimisation devices also mitigate harmonics, reducing losses associated with harmonic content on the electrical system. Transients Transients are large, very brief and potentially destructive increases in voltage. Their causes include lightning strikes, switching of large electrical loads such