The generation of AC electric power is commonly three phase, in which the waveforms of three supply conduits are offset from one another by 120°. Standard frequencies are either 50 or 60 Hz. The voltage across a pair of these conduits, or between a single conduit and ground is single phase electric power. Single phase power is what is commonly available to residential and light-commercial consumers. The design of induction motorss for single-phase power incorporates special design features to attain starting torque.