Most electrical circuits reside inside a chassis with input and output devices and power supply lines attached to it.

The chassis provides an electrical cage inside which circuits are protected from and prevented from interference with external circuits and environments. At the power connectors, inputs, and outputs this protection is at the weakest link, and additional precautions are required.

Surge-suppression is designed to protect the circuitry from high voltage surges such as may occur from lightning strikes, electrical short, power-supply disconnections, bounce and brownouts, and electro-static shock.