phantom circuit

noun Electricity.
  1. a circuit derived from two suitably arranged pairs of wires, each pair being a circuit (side circuit) and also acting as one half of an additional derived circuit, the entire system providing the capabilities of three circuits while requiring wires for only two.

Origin of phantom circuit

First recorded in 1880–85
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018