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I don't have much AC knowledge, but I am willing to learn. I've been surfing the web to find out more about outlet grounding. I still want to know more, that is why I am asking this here.

Grounding an outlet means to connect a third wire (apart from hot and neutral) to the earth by some conductive objects(pipes). This, I understand, helps prevent electrical shocks.

Now the questions:

  1. How is the ground wire connected to the outlet?

  2. If the ground wire is a path for electicity that protects you from becoming one, how does the outlet provide power at all?
    Why doesn't the entire current go through the ground wire?

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  • \$\begingroup\$ See Why don't we use neutral wire to ground devices .... It's not exactly the question you asked but may help. \$\endgroup\$ – Transistor Feb 4 '16 at 13:52
  • \$\begingroup\$ It's clear to me how grounding would help prevent a shock by touching the lamp casing.Now outlets are made from plastic.It 's just about touching the terminals in this case. \$\endgroup\$ – Daniel Tork Feb 4 '16 at 14:42
  • \$\begingroup\$ Grounding is there to protect you from faulty metal-cased appliances. It does nothing if the appliance is plastic, and those appliances may not even have a ground pin on the plug. The ground also does nothing to protect you if you touch a live wire directly. You need a GFCI/RCD to help you there. \$\endgroup\$ – Simon B Feb 4 '16 at 14:47
  • \$\begingroup\$ So that means anything that has a metal casing will be connected to the outlet's ground. \$\endgroup\$ – Daniel Tork Feb 4 '16 at 14:50
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    \$\begingroup\$ That msans anything with a metal casing should be grounded. \$\endgroup\$ – Robherc KV5ROB Feb 4 '16 at 14:51
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  1. By a third wire all the way back to your installation's main earth terminal (or whatever it's called in your country). That in turn is connected to the electricity supplier's ground, a solid earth stake in the ground, or both. You shouldn't just be connecting to random bits of metal that just happen to be nearby.

  2. In the normal course events all (or very nearly all) the current should flow between hot and neutral only. The wiring should be insulated from the appliance case or anything else that's conductive and touchable.

The ground is only used if a fault allows a live wire to touch something that is metal and grounded. By providing a low-resistance fault back to the supply ground, it discourages the electricity from going through you. If the system is well-designed, either a fuse will blow, a circuit breaker will trip, or a GFCI/RCD will trip.

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1:

  • The ground wire is generally connected to the outlet by a third conductor (wire) inside the "wire bundle" that connects the outlet to the circuit breaker box (or fuse box, if you still have one of those).
  • The circuit breaker box is connected to ground b 2 wires. One runs back to the utility pole with the 2 HOT wires, and the other connects to 1 or more 6'-8' copper-coated "ground rods" that have been hammered into the ground.
Wiring Diagram

2: Because of the way the power is "transformed" from single-phase high voltage on the transmission lines to split-phase 220V coming into your house (see image below), the power always looks for the "shortest" path to ground.
Transformer Schematic
This path is usually from the "hot" pin on an outlet, through your appliance, then back through the "neutral" pin on the outlet. Just in case (in case someone connected the wrong wire to the neutral pin), though, any part of an appliance that's metal and expected for you to touch is connected to the outlet's "ground" pin, to make sure there's no "hot" voltage on it to shock you.

NOTE: This description is of American wiring type. For all other wiring standards, there is no center-tap on the transformer, and (nearly) all outlets are 220V, but most of the basic premise still applies.

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  • \$\begingroup\$ Even if I didn't accept your answer,you clarified the matter to me and Simon's answer came to complete yours.Thank you! \$\endgroup\$ – Daniel Tork Feb 4 '16 at 15:01

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