| 摘要 |
A measurement circuit (4) is provided in a sensor casing (5). The measurement circuit (4) measures voltage obtained by current according to voltage at a power line (2). The voltage at a power line (2) is generated in a probe (6), which is mounted on coating of the power line (2) and coupled to a conductor of the power line (2) in a non-contact manner. A signal ground line (7) of the measurement circuit (4) is connected to a metal plate (8). The power line (2) is wired in a distribution board casing (1), and the distribution board casing (1) is connected to ground through the sensor casing (5) made of resin that is of an insulating member. A predetermined electrostatic capacitance is formed between the distribution board casing (1) and the metal plate (8), and a noise current passed through the measurement circuit (4) can be decreased by passing the noise current to ground through the electrostatic capacitance. |
