Chris Minns asks Sydney residents to keep washing machines off to avoid heatwave outages

Penrith in city's west reached 39.9C on Wednesday as premier called on residents to cut back on power usage between 3pm and 8pm

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Soaring temperatures and strained power supplies have prompted the New South Wales government to ask residents to reduce electricity use in a bid to avoid outages.

The premier, Chris Minns, said Sydney residents should avoid using power-hungry devices if they can during a crunch period, which was expected to last for five hours.

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