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Where possible, you'll receive prior notification of planned power outages which will let you know the affected timeframe.
While the power is off, treat all power lines, wiring and equipment as being live at all times as it could be restored earlier than planned.
Turn off your appliances at the wall. Use surge protectors for sensitive electrical equipment like computers and TVs to protect them when power is restored. Keep your fridge and freezer on and closed.
If you're dependent on mains powered electricity for critical medical support have an emergency response plan in place.