Southern California Edison was forced to cut power to 70,000 customers on the evening of March 8 after the Path 26 transmission line became overloaded. Electricity demand soared during the year?s first heat wave, said the California Independent System Operator (CAISO), which is investigating the cause of the overload. The outage, however, is not considered a sign of things to come this summer, maintained both CAISO and Edison. ?What CAISO was dealing with Monday was not that the state didn?t have enough power,? said Edison spokesperson Gil Alexander. A transmission bottleneck was the apparent culprit. Demand was high, but not at record levels. Edison?s peak load that evening was 14,100 MW, compared to the utility?s all-time peak demand of 20,148 MW last summer. CAISO called Edison at 6:21 pm and asked it to shed 200 MW of load, said Alexander, and then quickly called again and asked the utility to drop another 100 MW. Edison restored power at 6:42 pm after CAISO called off the emergency. Path 26, which runs through Central California, was rated at its full 3,000 MW capacity that day, said Gregg Fishman, CAISO spokesperson. However, it was overloaded with 3,250 MW, which threatened to damage the line and substations. The grid operator said it had asked Southern California generators to power up additional units as temperatures soared into the 90s in Southern California?s interior valleys. However, demand temporarily outstripped supply as people returned to their hot homes and turned on their air conditioners. Total state demand that day peaked at 31,777 MW, said Fishman, almost 1,000 MW more than projected. Generators in Northern California were producing plenty of power, but they could not send it to Southern California. Fishman added that in the summer more plants operate in Southern California, so CAISO has more options for dealing with peak demand. Edison spread the blackout among small groups of customers in 93 separate communities in accordance with its rotating outage plan developed during the state?s energy crisis, said Alexander. In addition, the company told numerous commercial and residential customers covered by interruptible service agreements to turn off air conditioning equipment.