A black box is a device that helps correct power factor by reducing kVAR usage. (The power factor in your home is the ratio of the real power performing work to the apparent power stored within the circuit.) Ameren Illinois' residential rate structure does not bill by kVAR-hour usage and only bills by kilowatt-hour usage. Please Note: If you are an Ameren Illinois electric customer, these devices will not lower your Ameren Illinois electric bill.
In alternating current, volt-ampere reactive (var) is a unit used to measure reactive power in an AC electric power system. Reactive power exists in an AC circuit when the current and voltage are not changing at the same time. Vars may be considered as either the imaginary part of apparent power, or the power flowing into a reactive load, where voltage and current are specified in volts and amperes, the two definitions are the same.
According to the government's National Institute of Standards and Technology (NIST), in a residential setting, these devices may not deliver the advertised savings.