Final answer:
A power wire touching the body ground causing a fault is known as a ground fault, characterized by a live/hot wire contacting the appliance's metal case. A proper ground connection causes the circuit breaker or GFI to trip, preventing electric shock and forcing the appliance's repair.
Step-by-step explanation:
When a power wire breaks off and touches the body ground, the kind of fault this creates is known as a ground fault. This occurs when the insulation of a wire wears out and the live/hot wire comes into direct contact with the metal case of an appliance, which could potentially be the ground connection. In the absence of a proper ground, this condition could lead to a severe electric shock, especially in environments where a good connection to ground is possible, such as near water.
If the ground connection is intact, however, the presence of a ground fault should prompt safety devices like a circuit breaker or a ground fault interrupter (GFI) to trip, thereby stopping the current and preventing exposure to electric shock. The GFI device works by comparing the currents in the live/hot and neutral wires, and it will trip if it detects a difference exceeding a safe value, indicating that leakage current is finding an alternative path, which could be hazardous.
The significance of a proper earth/ground wire cannot be overstated, as it ensures that, in the event of a fault, the electrical current has a low-resistance path directly to the earth, thus protecting users from potential shocks and forcing repair of the appliance for safe operation.