| 摘要 |
The apparatus comprises at least one input terminal (9) adapted to be electrically connected to an external conductor (7), a ground terminal (19) and a protection circuit (22) connected between the input and ground terminals. The protection circuit (22) comprises transient voltage suppression means (23). For testing purposes, a DC voltage source (25) can be connected between the input terminal (9) and the ground terminal (19). In order to make the transient voltage suppression means (23) inoperative during this test, means (27) are provided for interrupting the electrical continuity of the protection circuit (22). At least the protection circuit (22) and the means (27) for interrupting are accommodated in a housing (24). The means (27) for interrupting comprise mechanically operated on-off switch and operating means (47) are provided for operating this switch from outside the housing (24) in a closed condition of the housing.
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