A vacuum pumping system comprises a plurality of vacuum pumping arrangements for evacuating an enclosure and an auxiliary vacuum chamber for evacuation by at least one first vacuum pumping arrangement. The vacuum pumping system has a first state for evacuating the enclosure and a second state for conserving power consumed by the system. In a first stage of the second state the first vacuum pumping arrangement is arranged to evacuate an exhaust of at least one second vacuum pumping arrangement and in a second stage the exhaust of the first pumping arrangement is arranged to be evacuated by the auxiliary vacuum chamber.