This paper represents the analysis and countermeasure about the causes of various trouble-examples by the noise in plants. These kinds of troubles came out the mis-operation and damage in various kinds of operating-facilities. The cause-analysis is following as: 1) the inappropriate-applications of protection devices installed to protect the noise. 2) the causes of voltage difference in separate ground systems. Therefore, To resolve the noise problems in plants, This paper proposed the two kind solutions to a problem. 1) The installation of appropriate noise protection devices and 2) The organization of equal-voltage by the common grounding system.