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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There are a lot of redundancies in electrical wiring that become codified. Some stuff actually makes sense, and some stuff is pushed by manufacturers and distributors in order to make more money. When you start to think about why things are wired a certain way and can’t rationalize it anymore, there’s a good chance Siemens or Cutler-Hammer or whoever pushed to get a cash grab codified.
It’s worth mentioning that a neutral is always a white conductor, but a white conductor isn’t always a neutral. It’s good to have the bond in that instance in case things go south. Also, we have a LOT more electronics at home these days, and some of those electronically-controlled devices (dimmer switches!) need bonds and neutrals to function properly.
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In many countries in the world, probably all of them outside North America, that is not the case.
Here in Europe, only ground goes to a bus bar, which will be going into the actual ground.
The neutral stays next to the phase/live, and both go the distribution transformer somewhere in your street/neighborhood. At that point, the neutral is connected to the ground of the transformer.
neutral is common for all connections on that transformer. The European transformers are also much bigger than those funny bins people in the US have on a pole. Our transformers will be the size of a small van and power multiple streets.
By fixing the neutral to ground at the transformer, rather than at your house, they know for sure that the voltage difference between neutral and phase is what they want it to be. If the neutral was created at each house separately, there could be differences.
Because there is some distance between your outlet and the transformer, which might be 5 or 10 streets further, there actually will/can be a small voltage drop on the neutral. So if you measure the voltage between neutral and real ground, you might measure something like 2 or 5 volts.
In North America the power comes into your house as 240 volts carried on two live or hot wires. If you need 240 volts only you don’t need a neutral. Air conditioners for example generally only have two hot wires as they only need 240 volts. Many other appliances such as ranges will have the 240 volts and a neutral. This allows for both 240 volts (live to live) and 120 volts (live to neutral) to be available at the appliance.
Since most of the circuits in your house are 120 volts, it is provided by one live hot wire (typ. Black). But to complete a circuit you need a path back to the source. This is provided by the neutral (typ. White). The neutral can be considered as a center tap between the two hot wires provided by your utility. By doing this you end up with 240 volts from hot to hot, but 120 volts from hot to neutral. You should now be able to appreciate that the neutral is actually a current carrying wire.
The ground wire is a safety wire and is intended to only carry current in the case of a short circuit. If you use it as a neutral (bad idea) it becomes current carrying. This is not what you want.
The neutral is tied to ground at the panel to give you a zero reference. Voltage is a differential between two points. The neutral being tied to ground gives you the base reference.
Another poster stated that in much of the world, the neutral is not tied to ground at the service panel. In these cases it is very likely that the working voltage for the residence is 240 volts, not 120 volts.
You could use them the way you’re thinking (interchangeably) and the socket would still “work”. But it wouldn’t be safe.
The neutral is designed to carry the current back from the device in normal operating conditions.
The earth is designed to carry the fault current back from you (or something else) in fault conditions.
Earth is a safety wire. In normal circumstances you don’t “need” it, but in fault conditions you’ll be very glad you’ve got it.
Imagine a fault on a toaster where the live wire touches the metal casing of the toaster. The neutral isn’t touching the casing, so there’s no current: nothibg will trip. Until something touches the toaster to complete the circuit at which point there will be short circuit current.
That something could be you touching the toaster with current going through you to ground through your feet/hand touching the metal sink etc. Or you could just always make sure there’s a safety wire (earth) toucbing the toaster casing so that it takes the current instead of you.
In theory if everything always worked you’d need only one of them. But in practice, things break.
That’s why your dishwasher is grounded. A live cable in the dishwasher could contact the metal outside, and without that grounded you wouldn’t notice until you touched the machine and the sink at the same time. The sink often a good ground due to metal pipes, it would lead to a dangerous situation.
Now, why don’t you ground the dishwashee with the neutral cable?
First of all, anything that’s connected with a plug is not coded which is live and which is neutral. So, depending how you inserted the plug, the chassie would be either connected to live wire or to neutral. Not good.
Second, even if you ensuredwhich was neutral and which was live and their was a break in the neutral cable somewhere between the dishwasher and the panel, the machin would stop (no current flows, as their is a cable brake). No current through the heating element/motor means that the neutral wire would have the same voltage as the live wire. And remember that the neutral was connected to chassie…?
So, ground is a cable that’s must never ever be connected to a live wire, and if it happens to be connected by one fault, it will trip the fuse. Now, you can have two faults and get to a dangerous situation (ground wire broke AND lose wire!) .
I hope this explains it. It’s not due to physics, but to handling all sorts of faults.
To complete a circuit you need live and neutral, basically it’s not enough to pump electricity into something, it also has to have a way to escape to actually flow and deliver power. Ground is there to make sure that
A) IF current goes anywhere BUT from live to neutral, it has a better way to go to ground than through you
B) If you have any current going from live to ground you know that somewhere there are amps leaking out of a device so you have a special breaker that sensitively measures the amps through ground and if there are any the breaker has to trip within a very short time to, again, don’t allow live to deliver power through you if you touch the leak.
Ground is there to save you life. Neutral is there to power your stuff.
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.
One carries current under normal use and the other is only there to maintain a safe voltage level without carrying current (except in fault conditions). If only one wire was used there would be no guaranteed safe voltages at the parts of your appliances that you touch.
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