Feeders are medium-voltage lines that carry electricity from a substation (or some other kind of power supply source) to a smaller substation or to the consumer directly (the final branch-circuit overcurrent device). This block of power starts off at the service provider's equipment and winds up at a subfeeder panel or service panel. The device where the feeder circuit ends can be owned by either the service provider or the consumer. Here the circuit is broken down into smaller circuits.
Feeder circuits are three phase distribution lines. They are the power source to other three phase and single phase circuits. Feeders must be capable in carrying the amount of current required by the load, plus any current that may be required in the future.