  Electrons move along potential or thermal gradients. In the presence of a
global gradient, applied e.g. to the two terminals of a conductor, this induces
electric charge and heat currents. They can also flow between two equilibrated
terminals (at the same voltage and temperature) if detailed balance is broken
in some part of the system. A minimal model involving two metallic islands in
series is introduced whose internal potential and temperatures can be
externally modulated. The conditions for a finite electric flow are discussed.
