An apparatus includes a signal generation module that injects a signal in a pilot conductor with one or more AC components. The pilot conductor is connected to a grounding conductor of power cables connecting a power source to a load. A frequency change module periodically changes a frequency of each of the AC components, a current monitor module monitors current in the pilot conductor or ground return, an AC detection module determines an AC current for each AC component, and an AC threshold module determines if one or more of the AC currents determined by the AC detection module is below an AC threshold. A trip module opens a contact in response to determining that at least one of the AC currents is below an AC threshold for longer than an AC current time threshold. The contact disconnects the power source from the set of power cables.