Ripple control is a common form of load control, and is used in many countries around the world, including the United States, Australia, Czech Republic, New Zealand, the United Kingdom, Germany, the Netherlands, and South Africa. Ripple control involves superimposing a higher-frequency signal (usually between 100 and 1600 Hz) onto the standard 50–60 Hz of the main power signal. When receiver devices attached to non-essential residential or industrial loads receive this signal, they shut down the load until the signal is disabled or another frequency signal is received.