The surge test involves multiple
high-power noise injections to the signal lines. This high-power injection
charges up the PHY IC's internal circuitry, resulting clamp stages within the
PHY. Including a good path for common mode noise to discharge from the signal
lines to the connector ground is recommended to improve the surge test
performance. Good isolation between the connector/system, as well as a good
discharge path from connector to earth ground is crucial for surge test
performance with shielded cables.