In order to suppress both large current and arc discharge during hot switching, a grounding circuit is provided with: a first relay; a second relay; a third relay; a first resistance which is connected in series with the first relay to enable a feeding path to be connected with ground using the first relay; and a voltage divider which is connected in series with the second relay and the third relay, and which can be connected so as to divide a voltage between the feeding path and ground. The third relay is disposed at a voltage division point. When connecting the feeding path with ground, the first to the third relays are controlled such that the feeding path is connected to ground via the first resistance by the first relay, the voltage divider is connected in parallel with the first relay and the first resistance by the second and the third relays, and further the connection with ground by means of the first resistance is cut off by the first relay. When the connection of the feeding path with ground is to be removed, the first to the third relays are controlled so that a ground current can be cut off by the third relay.
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