The sudden and powerful electrical surge that knocks out your modem, kills your computer power supply, or toasts your motherboard, is very real but somewhat isolated. A far more common problem, that is much more difficult to spot, are the hundreds of smaller power surges and sags that negatively affect your system on a normal day, weakening vital electronic components and destroying data until there is finally a total failure.
Lightning is no longer the main killer of computers.
The smaller surges and sags that occur most frequently slowly degrade your equipment until it no longer functions. E xternal surges occur outside a facility and are generally caused by storms or normal switching operations of the power company and travel into a facility through AC power lines or telephone and cable lines. Internal surges are generated from within the building and travel throughout the AC lines within that facility. Internal surges are usually less severe than external surges, but occur much more frequently than external surges. W ith the increasing quantity and frequency of use of noise and surge generating electronic equipment, internal surges are occurring more often and with more strength.