Gyrotrons and High Voltage Power Supplies (HVPS) used on electron cyclotron (EC) systems are the source of large electromagnetic interference (EMI). Arcing events inside gyrotrons is the most frequently cited issue, but fast shutdown of a HVPS can produce similar effect. Even during normal operation, many diagnostics in the vicinity of the tokamak may be affected by the HVPS. The Swiss Plasma Center (SPC) has performed an electromagnetic compatibility (EMC) analysis of the ITER EC-system, in collaboration with F4E and IO. The analysis is based on lessons learnt at SPC (TCV tokamak and Falcon test facility). A conceptual design of the ITER Building 15 earthing system is proposed and a list of requirements relevant to EMC and to the earthing of the complete EC equipment has been established. The present article summarizes this work, presenting the key elements required to provide an optimal EMC environment to the ITER EC-system. Guidelines for a proper electrical installation of an EC-system in a fusion facility are issued, allowing for effective EMI mitigation and a reliable operation of the gyrotrons.