Reverse Supply also known as Backfeeding may occur when the power provided by the electrical generator is able to flow over the electrical service line. Because an electrical transformer is capable of operating in both directions, electrical power generated from equipment on the consumer’s premises can backfeed through the transformer and energize the distribution line to which the transformer is connected.

Backfeeding occurs when electric power is being induced into the local power grid. Power flows in the opposite direction from its usual flow. An alternating current (AC) power station typically delivers power to the power grid by inducing a current to flow into the power grid when the voltage is positive, and inducing it to flow out of the power grid when the voltage is negative, and a typical power grid load (e.g. factory or home) induces current to flow out of the power grid when the voltage is positive and into the power grid when the voltage is negative. If either of these types of facilities starts inducing current like the other, then backfeeding is occurring. Generators that are backfeeding pumping energy into the grid making it available for all to use.

A power station will typically backfeed when it is shut down, due to local loads (e.g. lights or repair equipment). A power grid load may backfeed if it has distributed generation installed, such as a grid-connected photovoltaic solar power system or a microturbine-based power generator.