More than 20,000 homes in Melbourne's south-east have lost power in the third mass outage in Victoria in recent weeks. Thousands of homes in Boronia, Ferntree Gully, Knoxfield and Wantirna were affected just before midnight on Sunday after a fault at Boronia substation. Traffic and street lights were also reportedly impacted before power was fully restored at 1.09am. A spokeswoman for energy company AusNet Services said sub-station equipment was designed to shut off power to isolate the fault. Sunday's outage is the third major blackout in Victoria in as many weeks. Almost 7000 Victorian homes were left without power as the electricity network buckled again under scorching heat last Wednesday when the mercury reached 38 degrees. Thousands of homes were left without electricity and air-conditioning in Melbourne's northern suburbs, with 3200 power outages recorded in Coburg alone by energy provider Jemena at 10pm. In the worst blackout, 41,000 homes were plunged into darkness across the state on January 28, with some residents enduring a 15-hour blackout. The state government and energy providers will pay Victorians up to $180 compensation for the inconvenience. Politicians have lashed power companies such as United Energy, CitiPower, Powercor, Jemena and AusNet Services in the wake of the blackouts. Energy minister Lily D'Ambrosio and Premier Daniel Andrews vowed to take energy providers to task. "Nobody should have to cop these situations," Ms D'Ambrosio told 3AW's Neil Mitchell. "People are entitled to have confidence in their energy system". "Our poles and wires and substations let us down." Ms D'Ambrosio said she expected the Australian Energy Market Regulator would investigate the shortage and if energy providers were meeting their infrastructure maintenance responsibilities.