I just added a circuit to my breaker box and it got me thinking about how the wiring all works. The neutral and ground both go to the bad bar in the circuit box, if they’re both in the same place then why can’t that just be wired inside the outlet and a single wire runs the length instead of two?
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Think of power flowing from the power plant down the live wire, through your equipment, back through the neutral and back to the substation.
For safety and practical reasons, the neutral is connected to earth at the substation.
Imagine what happens if the neutral wire breaks or becomes disconnected on the way. The neutral wires between your equipment and the break becomes connected to live and becomes dangerous.
For this reason, it is important that a safety earth connection be separate from the neutral. If the neutral wire breaks or becomes disconnected, and you connect earth and neutral together, your earth wiring can become live – as this is connected to exposed metalwork, this is extremely dangerous.
There is also a separate recommendation that your earh connection be of very good quality and highly reliable.
One option is to have completely separate neutral and earth connections. The neutral comes from the power company. You have your own earth electrode buried in the ground. The problem with this approach is that earth electrodes aren’t reliable and are of poor quality so don’t provide optimal protection – so require the use of additional protection such as RCDs (GFCIs). However, with good quality RCDs, this connection system is adequate and cheap,especially if you get extra “free” earth connections like underground pipes.
An alternative option is to have the power company provide separate neutral and earth connections. This used to be easy as underground cables used to use a lead outer sheath instead of plastic. The outer lead was buried in the ground and connected to the substation so it was a super good earth connection separate from the neutral wire. Now that lead cables are obsolete and being replaced or repaired with plastic this no longer works.
The next best option is the the power company to connect the neutral and earth and treat them as combined. But this is dangerous isn’t it? If the neutral wire breaks it is, or if an earth electrode fails it is. However, it is possible to work around this in a power grid. You can have highly reliable wiring – for example a loop so that a house is actually connected via a loop of cable to two substations. If the cable breaks at one point, there is still a backup neutral connection, so the system stays safe. Similarly, the power company can put an earth electrode at every pole as well as both substations. This makes the combination of earth electrodes super reliable.
This combined system works, as long as the power company use a highly reliable wiring design. If they do this, then you get a high quality, highly reliable and safe system. However, once you get into the house, it’s easier to treat them as separate.
The combined system is useful in dense areas, where there are substations close enough that the power company can guarantee high reliability wiring. This system is therefore often used in towns. However, out in the boonies, it may not be practical to use such a wiring design, so rural houses almost always use their own earth electrode.
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