Hello,
most non low-power electric devices have a ground pin to protect if a shortcut or something happens (Correct me if I got that wrong, already)
But how does it work? As far as I know you always need a completed circuit for electricity to flow. So how is an electric circuit closed if electricity flows to the ground?
In: Physics
there is a ground connection at the device but there is also a ground connection at the source of your power circuit. The second, pre-existing connection is the part you are missing that completes the circuit.
The power distribution network does connect to the earth at various points. At your home near your electrical service entrance for example you will likely either have a wire connecting to a copper rod that has been driven into the ground or connecting to metal water pipes that are buried in the ground. Upstream in the power network will be similar connections to the earth.
Those connections are what allow the circuit to be completed and power to flow.
An electrical circuit relies on both positive and negative electricity. This connection is what gives an appliance or electronic device the power it needs to operate. If something goes wrong, there will be a buildup of energy. This can cause the electrical connection and housing to store that excess power.
When an electrical malfunction occurs, this power will be stored in internal wiring and external metal housing. A static electric shock is a simple example. You’ll only notice this buildup when a connection is made to let lost the electricity being stored.
A circuit breaker will shut off when a short circuit occurs. However, without a grounding wire, the electricity will still be present.
A grounding wire takes the electricity that has built up during the malfunction and sends it outside of your home back into the ground. The grounding wire is typically connected to either a metal internal structure within the appliance, or on the external housing. When the malfunction happens, rather than having the energy build up in the circuit, it flows back to the ground and turns off the circuit.
The protection is by connecting the metal enclosure of the device, using metal wires, to the “ground” prong of the power plug, which in turn connects via the metal pipes that surround the electrical wiring in the house, to the actual ground.
This provides a *metal* link between the device enclosure and the actual ground, so that the electricity in a short can get to the ground very easily via metal conductors.
As opposed to that electricity getting to the ground by traveling through your hands, into your body across your heart, and out through your feet, when you touch the metal box enclosure of the device.
Basically, the electricity will follow a metal path to the ground rather than through your body.
The power plant is also grounded, so once in the ground, the electricity “returns” to the power plant. You can think of it as “power plant pushes out electricity through the wires” and it normally “returns” through the wires, but if a short-to-ground happens it can “return” through the ground too.
Not an electrician, but I watch a lot of Big Clive and this is my understanding of it. Electricity flows through a closed circuit between the connected hot/live and the neutral wires. The third ground wire connects to a metal casing or shroud or whatever that a person could touch but it usually* isn’t directly connected to the live circuit. What this does is create a direct path to ground if there is a short in the circuit, protecting the person touching the metalwork from getting shocked. This works because electricity wants to flow along the path of least resistance and human skin has a fairly high resistance compared to straight copper to ground.
* There are circuits that have the ground connected via a capacitor or something, and I’m not exactly sure how they work. I believe it has something to do with the capacitor making it hard to transmit power across unless there’s a surge.
The complete circuit for mains electricity in your house is from the transformer on the pole, down the hot wire, through your device, up the neutral wire, and back to the transformer
So how is ground able to complete this circuit?
Because we tied neutral to ground!
In your breaker panel all the neutral wires end up tied to all the ground wires which are all tied to a long metal rod in the dirt outside. This ensures that neutral is at roughly 0 volts relative to ground and hot is at 120VAC or 230VAC (depending on your country) and not 120VAC + 5000 VDC because the transformer is just floating at some high DC voltage.
Because we tied them together back at the panel, a valid path for current in the event of a fault case is also transformer->hot wire->short to device case -> ground wire -> breaker panel -> neutral return -> transformer
We leave ground on its own pin so that it isn’t carrying current and is always at 0V not 1-5V above depending on the current in the neutral wire.
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