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
*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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