Power is generated at the powerstation, gets sent through cables to our house, through wires into my microwave. My microwave has a fault so the current goes down the earth wire into the ground but then where? Where is the ground connected backup to this circuit to complete the link and allow the current to flow??
In: Physics
you asnwered yourself with the statement
the circuit is closed by its ground connection since that effectively means the eletricity flows into ground.
what causes the fault to trip is the fact this power doesnt return tothe smaller circuit creating a huge diferential, this is detected by system like GFCDs and causes the breaker to trip
The long and short of it is that you don’t *need* a complete circuit, its just the easiest way to explain eletricity. The standard water analogy explains this well: imagine electric lines as a water hose instead. If you cut one of the lines, its like you capped the hose at that point. Water/electricity is still pushing against the end, but has nowhere to go and thus doesn’t move. A complete circuit solves this problem of “nowhere to go” by pushing all the electrons in a loop, but its not the only solution. Ground connections solve this by essentially being a giant tank: electrons don’t get backed up because there is so much extra room in ground that you can just keep shoving electrons into it without affecting the overall makeup of it.
Effectively, the circuit your appliance is completed by the power station and the planet. When an appliance shorts to ground, its internal circuit is bypassed by the fault, so the current is not routed through its circuits as designed.
You basicly already answered your own question. The circuit closes through ground. The transformer that powers your house has a primary high voltage side and a secondary low voltage side. The secondary side of the transformer is grounded somewhere. What that looks like depends on the type of electrical network used in your region.
Now, if a electrical device faults through ground an electrical circuit is closed through ground and a current will flow through the earthing system of your house back to the transformer.
There also is a type of electrical network that either has a very high resistence connection to ground or is completly insulated from ground. Here only the appliances or machines are grounded, but the transformer is not. A single fault to ground poses no problem here. This type of electrical network is mainly used in huge factories or operating rooms in hospitals.
In Australian homes, we have both earth stakes and Main Earth Neutral links (MEN). When your microwave faults to earth, it travels along the earth wires in your home and back to your MEN link where it rejoins with the neutral wire back at the main switchboard, completing the circuit. It’s connected in a way so that your RCD’s will still trip.
An alternate path for the current is through the earth stake. Here is where things get a little strange. Because the earth is so big (im talking our literal planet), it can act as both an anode, a cathode and a standard neutral line. In other words, some current goes out to earth and just stays there. Some gets attracted by another, MUCH bigger earth stake out at the substation. And some goes straight to the aformentioned stake.
theres 3 wires. Hot, neutral, and ground. the hot carries the electricity to the appliance, the neutral carries it back so it can flow, and the ground provides a place for the electricity to flow to in case of an overload. some electrical things will work with only a ground (starter motor in your car for example) so the energy flows through the device and dissipates into the “ground” (eg the frame rail of the car). That’s not typical of ac power tho. im not an electrician though so reddit correct me.
*facepalm*
Every other answer here that says something to the effect of “it goes back to ground/earth through a ground/earth rod” is totally wrong. The electricity doesn’t go into the ground, and the idiom “electricity is always trying to get back to ground” is 100% untrue.
The *bonding conductor* (the term in Canada) is used to complete the circuit back at the panelboard where the circuit breaker resides. The bonding conductor—which in North America is usually a bare copper wire—is connected through the “ground” prong of the plug to the metal parts of the chassis of your microwave, and that bare copper wire goes all the way back to the panelboard. The neutral wire that normally completes the circuit is also connected back at the panelboard to the neutral *bus* (a bar of terminal contacts), which is itself *bonded* to the panelboard.
What I mean by *bonded* is that the neutral and the bonding (“ground”) conductors are *both connected to ground*, which is usually accomplished with a copper rod pounded into the ground outside your home. **The point of the ground rod is not to provide a path for current to flow back to earth, but to act as a reference point for the neutral and bonding (“ground”) conductors.** It means that the neutral and bonding conductors at your microwave, and in fact everywhere else in your home, will have no electrical potential between them (voltage between them is 0 V) because they’re already connected back at the source, and that the potential between the ‘hot’ conductor and both the neutral and bonding conductors will be the same (in North America mostly 120 V in a home).
This is important for a couple reasons. If your neutral and bonding conductors are 0 V relative to ground, by extension they are 0 V to YOU, because your potential relative to ground is also usually pretty close to 0 V. That means that anything else bonded to ground—like your microwave’s chassis—normally won’t have any voltage relative to you so you won’t get shocked by touching anything that is bonded. It also means that the microwave chassis and the hot wire of the circuit powering it are 120 V with respect to each other: same as the potential between the hot and the neutral. If your circuit didn’t have that bonding conductor and the hot wire came into contact with the chassis of the microwave it would make the chassis itself 120 V relative to you, which means if you touched it you’d get shocked.
Instead, if the hot wire touches the metal chassis the current will travel through that bare copper bonding conductor all the way back to the panelboard and complete the circuit. That wire has very low resistance—much lower than the circuitry of the microwave—which will make the current draw go waaaaaaay over the maximum rating of the circuit breaker and cause it to trip. This should all happen very quickly, protecting you from ever touching an energized microwave chassis and getting a shock.
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