Breakdowns can be caused by incorrect operation of automatic devices in the system and by errors on the part of the operating personnel. Dangers include overloading, overvoltages, short circuits, damage to insulating and supporting structures, mechanical damages and ground fault. Selective power blackouts can also be a deliberate policy in areas where the power supply or the infrastructure is insufficient.
Power failures are common in many developing countries and make it especially difficult to operate sophisticated computer systems and other equipment unless backup generating capacity is available. In Syria in 1993, for example, the average Damascus household and business was exposed to up to 8 hours of power cuts per day. In the mid-1990s in the Ukraine, whole towns received no electrical power for hours each day in an attempt to spread the insufficient available power over the whole country and thus prevent a system crash. In industrialized countries power failures may also be caused by failure of computer systems. In the USA it was reported that 126 power failures had occurred at 20 air route-control centres around the country directing traffic between airports. A further 495 failures had occurred at 181 airport-approach centres. Radar screens may consequently be blanked for up to several minutes. Many such failures occur as the result of the use of antiquated equipment whose modernization has been delayed.
In the summer of 2001, three-quarters of the 170 million Brazilians were told that they must immediately cut consumption by 20 percent or face rolling blackouts and unscheduled power interruptions. The measures were needed because of an exceptional drought (Brazil obtains more than 90 percent of its electricity from dams and has not invested extensively in alternatives). Outdoor street lighting has been cut by one-third, and nearly every nighttime activity in major cities was affected. Few ordinary Brazilians had any inkling of the seriousness of the crisis. Officials warned that it may become necessary to order the nation to adopt a four-day work week, giving employees Mondays off until the end of the year.