| 摘要 |
A monitoring module associated with a three-contact receptacle injects an RF supervisory signal into the line contact. When a power cable with a two-contact plug is inserted into the receptacle, a ground fault in the electrical equipment served by the cable provides an alternate path to ground for the injected RF supervisory signal thus reducing the RF current flow in the neutral contact. Such reduction is sensed in a differential amplifier and used to disconnect power. When a power cable with a three-contact plug is used, a discontinuity in the ground path reduces the RF current flow in the ground contact due to the injected RF signal. This reduction is sensed and used to disconnect power.
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