I don't understand the concept of grounding a circuit for safety reasons, in this circuit that I simulated, imagine my hand touching the circuit as the closed switch. I am creating a closed loop between my body and the circuit letting current to pass through me. If the circuit was isolated or floating however, it would be impossible for me to get zapped because there would be no closed path for the current to flow in and out. So what is the point of connecting the circuit to the earth ground? And secondly, does connecting any point in a circuit to the earth ground pull the voltage in that point to the ground level?
Answer
Ground used for safety is a completely separate concept from the ground in low-voltage circuits. While the latter is just a reference point with low impedance to power supply terminals, the safety ground is a completely separate circuit which normally carries no current.
In modern installations (with diff current protection) any current in the ground wire above a certain threshold leads to immediate circuit breaker tripping. This protects the person who somehow managed to touch a live wire, like in your example. The only way to get shocked without tripping the protection would be to touch both hot and neutral wires, while NOT touching the ground.
In older installations, ground wire is simply connected to conductive parts which could be touched, like metal cases (most often TN-S earthing, but other earthing systems exist). This guarantees that metal cases can't go live without provoking a prompt short circuit. Of course, if you open the case and manage to touch a live wire inside, there will be nothing to protect you.
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