The former fourth couplings and solutions having been described in Chaps. 2 – 6 , this fifth coupling path reviews the various disturbances existing on the power mains, finding their way from their source to the electronic components of a system. After a quick analysis of equivalent circuits for typical power distributions, the impedance profiles of US power line mains in the 20 kHz to 30 MHz range, is shown, as a rationale for the 50 Ω LISN. This introduces power line filters and their effect on power line immunity and power line emissions. A full example of the parasitic emission from a switch mode power supply is carried-on, leading to the choice of the optimal filter described next. Filters are of no use against long duration (>μs) transients, so transient voltage suppressors (TVS) are explained, including metal oxide varistors, Zener-based TVS, and gas tubes. Handy figures, tables, and graphs help selecting the proper device. Isolation transformers and Faraday shielded transformers are completing this chapter, along with back-up and uninterruptible power supplies.