So how does the ground connection protect people from faulty appliances such as when a frayed live wire touches a metal casing. The ground wire is designed to redirect this charge into the ground through the rod but according to this illustration, if you have a single ground connection no current flows. So how does the charge of a faulty appliances get redirected?
Well, let's take a look at an example of how this might work in a typical house in the United States. This example shows an installation that has no GFCI.
On the left side of the image, there are two devices. The first device is the 120 V 60 Hz incoming power feed, which has two wires coming out of it: the hot wire (shown in green) and the neutral wire (shown in gray). The second device is the ground rod.
Next is the circuit breaker panel, which contains two important things. On the hot wire, it has a circuit breaker (represented here by a fuse symbol). The other important thing it contains is a connection between the neutral wire (from the incoming power feed) and the ground wire (from the ground rod).
Out of the breaker box comes a cable which contains three wires: the hot wire, the neutral wire, and the ground wire. This cable connects to some kind of household appliance. The hot wire and the neutral wire are both connected to some kind of load (represented here by a resistor), and the ground wire connects to the case of the appliance. There's a complete circuit here, and the circuit has an 8 ohm resistor in it, so only 15 A of current flow, and the circuit breaker does not trip.
Now, what happens if a frayed live wire touches the metal case of that appliance? Then the circuit looks more like this:
Now a new complete circuit has been formed. The circuit starts at the incoming power feed, then goes into the breaker box, through the circuit breaker, out of the breaker box, through the hot wire, into the appliance, through the ground fault, back out of the appliance, through the ground wire, into the breaker box again, through the ground–neutral connection, back out of the breaker box again, and finally back to the incoming power feed.
This new circuit has very little resistance, so a huge amount of current will flow, and the circuit breaker will trip.
Notice that the ground rod doesn't actually play any role in this particular scenario. If the ground rod were missing, exactly the same thing would have happened.
Where the ground rod comes into play is if a hot wire touches, say, a metal fence outdoors. The metal fence probably doesn't have a ground wire attached to it, but the fence is in contact with the earth (the actual soil around the house). The ground rod is also in contact with the earth, and the earth conducts electricity (as long as it's not too dry!), and so a complete circuit is formed that way.