5th and 11th Harmonics – The 5th and 11th harmonics are also of particular concern to industry today. Although the 5th harmonic is much more prevalent, both have a negative sequence. This means that when distorted voltage containing the 5th or 11th harmonic is applied to a 3-phase motor, it will attempt to drive the motor in reverse, creating a negative torque. In order to compensate for this negative torque, the motor must draw additional fundamental current. This, in turn, can cause overheating and/or the tripping of over-current protection devices. 6-Pulse adjustable speed drives are a major source of the 5th, 7th and 11th harmonics. 12-Pulse drives are significantly more expensive, and are a source of the 11th and 13th harmonics, but through their design are able to eliminate the 5th and 7th.