A power failure due to an energy surge is when the electricity of one or more customers goes out due to higher electricity demand on PG&E’s equipment than the equipment is designed to handle. Power surges occur when the flow of electricity is interrupted, then started again, or when something sends electricity flowing back into the system. When the frequency reaches its minimum or maximum level, there is a risk of failure of transmission lines. The breakdown of transmission lines due to over or under frequency is called Power Grid Failure.