What must properly selected grounds be able to carry to trip out the circuit?

Properly selected grounds must be able to carry fault current to trip out the circuit. When a fault occurs in an electrical system, such as a short circuit or ground fault, an excessive amount of current can flow through the ground. This fault current must be sufficient to trigger protective devices, like circuit breakers or fuses, to disconnect the faulty circuit from the power supply quickly, preventing damage to equipment and eliminating safety hazards.

The ground system is designed to ensure that during such fault conditions, the electrical current has a reliable and low-resistance path to flow, allowing the protective devices to operate correctly. Inadequate grounding may result in high voltages appearing on equipment frames or other conductive surfaces, leading to shock hazards or equipment failure.

In contrast, other options do not reflect the primary role of grounding. Load current refers to the normal operational currents, while voltage and residual current pertain to different aspects of electrical systems that do not directly deal with the safety function of grounding under fault conditions.