Debilitating strain on the province's power grid yesterday forced electricity providers in Calgary to institute rolling power outages to alleviate pressure on the taxed system.

Calgarians were sideswiped late in the afternoon by outages that left offices and homes in the dark, wreaked havoc on city street lights, stalled C-Trains and elevators, and kept emergency services struggling to keep up.

Enmax, as well as other electricity providers in the province, were ordered by the Alberta Electricity System Operator to implement rolling outages in their service areas to alleviate the stress on the grid, said Enmax spokesman Rocco Ciancio.

The supplier cut power to the city's 36 power regions, one area at a time, said Ciancio.

Unannounced rolling blackouts around the city yesterday and interruptions in phone service are being blamed on the weather.

All that comes as the Alberta Electric System Operator (AESO) called for a voluntary reduction in electricity use to combat a higher than usual demand sparked by the recent heat wave.

"The Alberta Electric System Operator's forecast shows that the last few days of unusually hot and humid weather has increased demand for electricity, primarily due to the higher use of air conditioning and irrigation systems," said spokesman Nancy Janes.

Around 4:45 p.m. power suddenly went out in homes and businesses downtown, in Bonnie Doon and Londonderry shortly before EPCOR spokesman Doug Downs issued a statement saying Edmonton's power company was responding to the energy-saving directive with 20 to 30-minute rolling power outages throughout the city.