| 摘要 |
PURPOSE:To prevent an electric conductor from being damaged during underground installation operation by sending low voltage current between a tool and a conductor so that contact between them can be detected. CONSTITUTION:A secondary side coil is connected through a relay 2 to a contact terminal 5 of a tool's main body and a contact terminal of an underground installation object 6, and it is operated in the condition that an output voltage of a normal transformer is impressed on it. On the other hand, a direct circuit for a all-time-open contact 22 of a relay 2, a bell switch 7 and a bell 8 is connected to a power source through a power source switch 1. In such a mechanism, when the relay 2 is being driven, if the tool contacted an underground laid object, the all-time-open contact 22 is closed, the bell switch 7 is closed and the bell 8 is sounded to give a warning. At the same time, by operation of the relay 2, the all-time-close contact 21 is opened and power supply to an electric tool M is discontinued. |
