In test circuits, the resistors serve to adjust defined conditions for the unit to be tested.Load resistors act on the power supply with their nominal current or discharge batteries.In test circuits for switchgears and semi-conductors they may be used in combination with condensers and reactance coils to adjust defined currents at nominal voltage.Test resistors must be adjustable within specified limits as a function of the respective application. They should be robust and dimensioned such that they can also survive limit loads and possible stepping errors without damage.