Today's equipment is extremely vulnerable to voltage surges and electrical transients. Many of the components that make up the integrated circuits operate at low voltage, making them particularly vulnerable. Voltage surges and transients cause degradation of these circuits and eventually will lead to a failure.
Common causes are lightning strikes, Electrostatic discharge and operation of large electrical motors. Power company equipment failures, line failures and even neighbors with large power equipment can cause voltage surges, drops, ground potential changes are all possible causes of damage to electrical equipment.
Equipment has two sources of potential surges, the power supply and the communication lines.