Two Sided Earthing Versus one Sided Earthing for Ethernet Cables

The discussion about the earthing method of Shielded Twisted Pair (STP) cables never stops. There is a difference in opinion between Local Area Network (LAN) equipment manufacturers and Electromagnetic Compatibility (EMC) specialists. LAN equipment manufacturers state that the cable screen should only be earthed on one side of the cable, because it can prevent a ground current loop. EMC specialists advise multi-point earthing, since it is the best way to increase immunity to different kinds of disturbances. To find out which earthing method gives better results, a few measurements are performed. Three kinds of test methods are used: a direct current injection (50 Hz) test, an electric fast transient bursts (EFT-B) test with a capacitive clamp and a continuous wave (CW) test using an Electromagnetic (EM) clamp.