In this study, a ubiquitous sensor for condition monitoring of insulators and lightning arresters installed in power distribution lines and electric traction vehicles is presented. The sensor consists of two parts; a leakage current measurement and a lightning surge detection. Measured data are transmitted to a supervisory computer through ZigBee protocol based on IEEE 802.15.4. To detect leakage current, a window type Mn-ZCT is used and a low-noise amplifier with a gain of 60dB is designed, and this can measure leakage current in ranges of $100{mu}A{sim}5mA$. A sample-hold (S/H) and a Rogowski coil are injected to analyze the magnitude of surge current in ranges from 100A to 10kA with $8/20{mu}s$-waveform.