In spite of high levels of service security, power supply disruptions still occur regularly at power distribution system operators or power supply companies. Most of these malfunctions are so short (less than one second long) that consumers do not even notice them. However, interruptions lasting longer than 10 ms can cause disruptions to IT operations. In addition to malfunctions in the power supply system, however, switching off equipment when performing scheduled maintenance or cables damaged by excavation work can also cause the power supply to be disrupted.
Note that not only the obvious, direct consumers of electricity (PCs, lighting, etc.) depend on the power supply. Much infrastructural equipment used today depends directly or indirectly on electrical power, e.g. lifts, air conditioning technology, alarm systems, security gates, automatic door closing units and sprinkler systems. Even the water supply in high-rise buildings relies on electricity to generate water pressure on the upper floors using pumps. If the power supply disruptions occur over longer periods of time, disruption of infrastructural equipment can mean that no more activities can be carried out in the affected areas.
Apart from disruptions, other malfunctions of the power supply can also impair operations. Overvoltage, for example, can result in malfunctions or even damage to electrical devices.
It must also be noted that the organisation's own business processes may also be affected by disruptions or malfunctions of the power supply in the neighbourhood under certain circumstances, for example if access roads are blocked.
Examples:
Due to an error in the UPS of a computer centre, the UPS did not switch back to normal operation after a brief power failure. After about 40 minutes, the batteries were empty and all the computers in the affected server room failed.
At the beginning of 2001, there was a power emergency in California that lasted over 40 days. The power supply situation was so tight that the Californian Independent System Operator mandated rolling blackouts. These power outages, which lasted up to 90 minutes, not only affected households, but also companies in the high-tech sector. Since the power failure also caused alarm systems and surveillance cameras to be switched off, the power supply company kept their rolling blackout timetables secret.
In November of 2005, many communities in Lower Saxony and North Rhine-Westphalia were without power for days after heavy snowfall because numerous power line towers had collapsed under the weight of the snow and ice. It took several days to restore power.