[ELI5] What does it mean to be “grounded” against electricity, and why does it keep you safe?
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Electricity does not have a tendency to flow to ground. That is a common misunderstanding.
However, when a piece of electrical equipment is connected to the earth (via a metal rod in the actual ground), it is commonly considered “earthed” or “grounded”.
The reason is for safety of electrical shock. Electricity flows in a loop. It must complete a circuit back to where it came from,and it takes all possible paths. However, it prefers the easiest path.
So under normal circumstances, power is generated at the power plant, goes down the power line to your house, to the equipment, then back down the wire and power lines back to the power plant.
Now imagine what happens if you have two pieces of electrical equipment. In one, the incoming wire comes loose and touches the case. In the other, the return wire comes loose and touches the case. You then walk past and touch both cases, you now complete the circuit and get shocked.
To protect against this type of problem, metal equipment cases must be connected to a common point, so that if you touch two pieces of equipment at the same time, you don’t get a shock. Most power flows through the wire connecting them togetger, instead of you.
Because you are standing on the ground or washing with water in metal pipes in the ground, then it makes sense that the safety bond is also bonded to ground. So, that there is already an easier route for power than through you.
Finally, because you don’t want loose wires to go unnoticed, you need some way of detecting faults. This is easier if the power plant is also connected to ground. This way the ground itself completes a circuit of a wire comes loose and lands on the ground (or touches the case of equipment). There can then be fault detection systems in your home which detect this power flow to ground and cut off the power.
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