Editing Power-line communication (section)

== Ripple control ==

[[Ripple control]] adds an audio-frequency tone to an AC line. Typical frequencies are from 100 to 2400 [[Hz]]. Each district usually has its own frequency, so that adjacent areas are unaffected. Codes are sent by slowly turning the tone on and off. Equipment at a customer site receives the codes, and turns customer equipment off and on. Often the decoder is part of a standard [[electricity meter]], and controls relays. There are also utility codes, e.g. to set the clocks of the power meters at midnight.

In this way, the utility can avoid up to 20% of capital expenses for generating equipment. This lowers costs for electricity and fuel usage. Brownouts and rolling blackouts are more easily prevented. Grids that use [[Combined cycle|cogeneration]] can enable auxiliary customer equipment when the generators are being run to generate heat rather than electricity.

An annoyance for customers is that sometimes the code to turn equipment on is lost, or load shedding is inconvenient or dangerous. For example, during a party, a dangerous heat wave or when life-preserving medical equipment is on-site. To handle these cases, some equipment includes switches to circumvent load shedding. Some meters switch into a higher billing rate when the ''party switch'' is flipped.