The grid transmits electricity to our houses through wires. Our Bryan Cockfield has introduced it well in his "Grid Secrets" series, but what role does the earth play? As we all know, it is used for security, but did you know that it is also used for power transmission in some cases?
Shown here is a diagram of a very typical house grounding system, as well as some current-carrying conductors commonly referred to as live and neutral wires. On the far left is the transformer outside the house, and on the far right is an electrical plug-in. Between them is a circuit breaker panel and a North American style wall socket. The green dashed line shows the normal path of current flow.
Please pay attention to the ground electrode used for electrical connection with the earth. Taking the National Electrical Code (NEC) as an example, Article 250.52 lists eight types of ground electrodes. A very good type is the electrode wrapped in concrete, because the concrete continues to absorb moisture from the ground and forms good physical contact due to its weight. The other is a ground rod or pipe that is at least eight feet long and inserted deep enough into the ground. Deep enough, we mean to include some factors, such as the frost line cannot be counted as a good ground because it has a high electrical resistance. You must be careful when using metal water pipes that appear to enter the ground, because some of these water pipes are usually replaced with non-metal water pipes during regular maintenance.
Also note that there are various metal enclosures connected to the grounding system in the picture. This is called bonding.
Now, how can grounding all these systems help us? Let's start by dealing with failures.
One purpose of the grounding system is to trip the circuit breaker in the circuit breaker panel when a short circuit occurs somewhere. This can happen if there is an appliance with a metal shell and the insulation layer of the live wire in the appliance is damaged, causing the copper wire inside to contact the metal shell. The shell becomes an extension of that line of fire. This is called a malfunction.
But the metal enclosure is connected to an electrical path consisting of the ground wire in the power cord plugged into the wall outlet and the wire from the wall outlet to the circuit breaker panel. In the National Electrical Code (NEC), these are called equipment ground conductors.
At least in North America, in the box where the service first enters the house, the equipment ground conductor is connected to the neutral wire. In this case, the box is the main circuit breaker panel. In most circuit breaker panels, this connection is achieved by connecting two wires to a metal strip that is screwed or glued to the panel housing, thereby making electrical connections through the housing.
Along the red dashed line of the fault, the high current now flows through the live wire, through the enclosure of the device, and uses the device ground wire as the return path for the circuit breaker panel. From there, the current passes through the housing of the panel to the neutral bar and the neutral wire back to the transformer. Along the way, the live wire passed through the circuit breaker in the circuit breaker panel, and the current was large enough to trip, disconnect the circuit and make it safe again.
But where did the earth come from? Usually not. However, sometimes, as shown by the blue dashed line, a small amount of current flows through a parallel path that includes the ground electrode and the ground.
Many people on Hackaday are very familiar with one purpose of grounding, which is the release of stray charges and static electricity to electrostatic sensitive devices and components (such as MOSFETs, CMOS ICs, and TTL chips). The way to deal with this situation is to wear an anti-static belt or work on an anti-static mat. These usually have a clip or a dedicated socket for connecting to the earth.
The charge on your body will put you at a different potential than the ground, so current will flow between you and the ground. The earth is electrically neutral to a large extent, it is easy to absorb the charge, so that the combination of the earth and you remain neutral.
Not all electrostatic discharges are accidental. We have introduced [Kevin Darrah]’s experiment before. He deliberately tested its impact on various components and tried a protective circuit.
Metal shells may also be charged by indirect lightning strikes, and any accumulated charge will flow to the ground in the same way.
In order to save costs, mainly in rural areas or remote and isolated houses, sometimes only one wire is used for transmission. This eliminates the cost of the neutral loop, provided that the cost savings make up for the reduced efficiency. The reduction in efficiency is due to the use of a higher resistance ground as the return path. Facts have proved that this is very safe. Australia and New Zealand have more than 200,000 kilometers of transmission lines using this method. In the United States, it is used in parts of the Midwest and Alaska.
Electricity is first provided by the grid to the primary of the isolation transformer, thereby isolating the grid from the ground. Here, the voltage is usually reduced from 22 kV to 19 kV. One side of the secondary is a single transmission line, and the other side is grounded.
Then use a distribution transformer at the customer site to convert 19 kV into a voltage suitable for the customer, such as 240 volts. One side of the primary is a single wire, and the other side is grounded for return, and finally returns to the ground side of the isolation transformer.
Soil resistance is a problem. The conductivity of dry soil is lower than that of wet soil. In Alaska, the ground rod must extend below the permafrost layer because the conductivity of ice is also poor. In addition, this higher resistance also causes the primary voltage to float higher and makes self-resetting circuit breakers difficult to reset because they rely on potential differences.
Additional phases can be added by adding second and third transmission lines.
Have you tried to create a good earth experience? Maybe you have encountered too dry soil and have to fix it? Or, as often happens, you are working in a place where you are sure that some wall outlets have no ground connection at all. Please let us know in the comments below.
Or go to the live side of the power distribution and check out Bryan's Grid Demystification series.
I think what confuses some people is seeing the neutral and ground wires in the circuit panel.
http://www.esgroundingsolutions.com/why-do-you-have-to-bond-the-neutral-and-the-ground-wire-in-the-main-panel/
Grounding is not always the case. Isolation grounding is used in many systems where electrical noise is a problem, and in some cases the same home run is used to return to the box, but it neglects to connect the neutral wire to the ground bar so that it can be directly grounded. It is most commonly found in hospitals, not residential or commercial buildings, but there.
The isolated ground is actually connected to the neutral point at some point in the system. Its isolation simply means that it is not directly connected to the typical ground used. Examples of these typical reasons are your metal conduit boxes, pipes, etc. Everything else is easy to use. The isolated ground is a separate wire that is directly connected to the ground terminal of the device and returned to the panel (not necessarily the panel that supplies power to the socket, it may be the upstream panel). Local hospital (one of the top three in the United States) I have never encountered IG in 10 years of doing electrical design for them. I do see that IG is in retail and restaurants, usually built by "design and build" contractors who know very little about the purpose of IG, except that POS computer vendors say they need those orange sockets.
Imma is going to put on my electrician's hat and take the oath of office! One thing people sometimes miss when reading NEC and related documents quickly is the difference between "grounded" conductors and "grounded" conductors. GroundED is the neutral point-it causes the voltage between this point and ground to be zero (the voltage at any point may not be zero because copper has resistance) and is expected to usually carry current (so if you cut it off, there will be It may be that there is a large voltage difference between the two ends). The grounding conductor can provide a good grounding connection for the connected things, so that if the above-mentioned charged refrigerator fault occurs, there is a better grounding path, instead of passing through some random people who just want to drink beer and turn on the tap at the same time, when they touch the present When the 120-volt refrigerator frame is charged, they will hold a grounded faucet. Instead of blowing up an unsuspecting person later, blow the fuse immediately.
True story: I once ended my job at a job, where I changed the electrical service of a house, where the wires on the street went underground through old metal pipes. When I poke something, I was shocked several times by accident and was very confused. Then I poke it with my voltage tester and found that the actual pipe carrying the wires from the street was live. The local natural gas company has been digging nearby, and their equipment ruptured the power supply pipeline, resulting in a gap in the wire. The pipe itself is corroded too badly, and there is no good connection between the outside of the pipe and the ground, so it will not cause a huge short circuit detected from upstream, but the freshly broken edge is well connected with the missing wire.
The current flowing through the earth is also the reason why we encounter the problem of geomagnetically induced current-it has become an unintentional single-wire transmission scenario, which can produce (mainly) DC voltage offset, can push the transformer out of the safe working area, and Things are completely messed up.
Quote: The difference between a "grounded" conductor and a "grounded" conductor. This is a difficult problem for many people. I have an electrical inspector who knows I am an engineer but not a licensed electrician and asked me "Where is the grounding conductor" ? Show me the grounding conductor". I will especially show them the point where the grounding conductor (from the grounding rod) is connected to the grounding conductor (the neutral connection bar) in the service entrance. Then they are usually, "Okay, okay, Now this looks like suspiciously neat wiring, like the homeowner did it :-)"
My God, you restored me a little confidence in your field. Most people I meet know the code, but when it comes to why this happens, they don't know anything. I had an argument with a dispute about the standard 120 or 220v mig welding machine is a low-voltage high-current device. He swore up and down that he could increase the welding voltage to more than 100v. When I asked him why he can put his hand on the workpiece for welding and talk about it here, he said you can't touch it. I forgot another point of detail, which made me feel scared, but it involved long-term operation, and he showed a lack of understanding of i^2*r.
Is there no differential fuse in the United States? In newer installations in Europe, I think this is the standard configuration. The differential fuse closes when hot (here: live) and neutral current are different. This difference may be much smaller than 16 amps or the main fuse you own. Because of this, it can even handle small leaks between the line of fire and the ground, such as through the human body or moisture.
Ground-fault circuit breakers are common in the United States—usually built into sockets and can protect the plug and anything that feeds downstream from the “load” terminal on the GFCI. I want to say that it will trip if there is something like 4 microampere difference, but I am too lazy to search for it on Google, so I may not know at all. GFCI sockets need to be used in wet areas, including kitchen counters, bathrooms and outside areas, and are also used to make traditional ungrounded sockets safer. In the past 15 or 20 years, AFCI, or Arc Fault Circuit Breaker, appeared in the United States, which looks for arc faults instead of ground faults. Residential bedrooms and other similar locations need them, so people sometimes only use afci circuit breakers to modify existing circuits. In most cases, changes to existing wires do not require changes to existing circuits to make them comply with the current NEC standards, but this does not apply to the requirements for installing AFCI, so if you touch it frequently anyway, if you In new buildings, you need to add AFCI protection to the circuit.
(None of this applies to the situation I said, there is no circuit breaker between the bare wire end of the basement projecting pipe and some large transformers upstream)
Okay, so I understand why it is not in the schematic above. In Europe, GFCI is usually installed with overload fuses
This is sometimes done in the United States, but it is more expensive than installing GFCI on the first socket of the circuit.
Yes, there is a GFCI circuit breaker on the panel of my mobile home in the 1980s, but there is also a GFCI socket in the garage because it was added later.
It's great to be able to test and reset from the source without having to trek to the panel.
I grew up in an old house, and there were two wires in the old house. I entered the computer and all these things came with 3 pin cords. For this, the GFI socket is a good solution because (if I remember correctly) it actually allows the GFI socket to disconnect its ground pin in this special case (when there is no ground wire). This is obviously a huge taboo in any other socket, but GFI makes up for the lack of grounding, at least from an electrical safety point of view (in principle).
When a handyman in the extended family remodeled my mother's bathroom, he rode on his high horse and wondered when the originally added add-on was connected to the bathroom and indeed had GFCI protection. My mother asked me about it, I told her it was protected, and told the "expert" that the protection was installed on the service panel. It turns out that experts did not know that they once existed as devices installed in the pane. I added this plugin shortly after the GFCI required by NEC, and yes, they are very expensive. The equipment has been used for ten years without failure. The cheap socket positioning equipment I used in my later work often failed. The point is that I have to wonder whether the more expensive panel positioning equipment is worth the money.
Circuit breakers with built-in GFI are a very painful thing. The only thing more frustrating than a GFI circuit breaker is a socket that is daisy-chained to a GFI socket. This was common when GFI outlets first appeared, and they were in the middle double-digit popularity. You can put one in a room and connect other sockets with a daisy chain, and they are protected by it. Of course, the problem is that many people don't know this, so they pop up the GFI instead of looking for the popped circuit breaker, but don't find it... If they are lucky, they will find the popped GFI before calling for expensive help.
The GFI circuit breaker is a real pain, because if you do something stupid and pop it, it's more than just eliminating the stupidity and pressing the reset button. It's more like you get rid of the stupidity and start walking wet, cover the distance in the basement with a towel, and then look around in the circuit breaker box to reset things. If you can’t see how this will unfold, please wait until someone in your house throws a hairdryer in the sink after showering, it will make a lot of sense.
What are the use cases for hair dryers and sinks filled with water? Who TF will do this, GFCI or not? I will have someone in my house tried this situation.
@Fred...think about Silvia Plath, but electrical
Some building codes require house-level GFCI, but interrupting too many power sources due to a single fault can be dangerous. The GFCI on the bathroom socket is good. It can prevent the person in the bathtub from being killed by a defective smartphone charger. However, it is much better to just cut off that socket than to cut off all the power in the house, leaving a person sitting in the bathtub in the dark room. This creates its own danger.
As others have pointed out, many GFCIs installed at the beginning of the trend can provide protection for all outlets away from the circuit breaker panel. Put it on the first socket in the kitchen, all other sockets are protected.
GFCI is very cheap. There really is no reason not to install each circuit on a separate GFCI. You shouldn't be in the dark because of the GFCI tripping. ...Of course, the mouse bit the lamp. :-)
In the UK, a new consumer unit must be a shunt load, that is, at least 2 RCDs (GFI), so that 100% of the consumer circuit will not fail due to the interference current in an RCD.
I wanted to write something, but I changed my mind. Just don't believe anything. Test it yourself and be safe. I have been an electrician for more than 30 years. And never trust anyone or anything. I was still electrocuted. Sometimes even God hates me. One thing I want to say. I did some really cool things. And went to places you never dreamed of.
As safe as possible...
The grounding problem caused serious damage to the audio equipment. I have encountered a situation where grounding causes potential problems between the ground rods, so my amplifier at the back of the house and my direct box in front of the house will cause problems unless the ground between them is lifted.
I also had to re-wiring several times overseas, because the misunderstanding of grounding caused unsafe conditions. For example, simple items such as "grounding" of water pipes are not enough, the neutral wire and the ground wire are not connected, or the ground rod is not connected. Add to a floating grid.
My understanding is that breaking the ground loop is an important reason why the MIDI specification requires a current loop signal.
In some places, grounding water pipes is a very bad idea. The soil will corrode the pipeline.
Or more importantly, the pipes have been replaced by plastic in invisible places.
Our house in 1910 suddenly leaked. The plumber traced a severely corroded water supply pipe outside the water meter near the street. When he cut the pipe, he received a severe electric shock!
It turns out that the squirrel has bitten off the neutral wire on the pole transformer, and the house has been grounded through the water pipe, so it has become a neutral wire. All the electric current corroded the pipeline. Neutral fixed, replace the service tube with plastic, everything is normal.
true story. The wife is taking a shower. I am in the kitchen. I turned on the light and she yelled!
She complained and was shocked. Shocked to tell you. Next is a large-scale investigation of voltage and action. When the kitchen light is on, the voltage from the shower head to the drain is 110 volts, and it is 0 when it is off.
I did some exploration, but found that there are two major problems with the wiring in this lease. One-the light fixture above the sink clamps the hot wire to the housing, causing a short circuit to ground. This is evident in the visual inspection-it is easy to fix. But why was there no fuze before? Could it be that there is no land?
The system is grounded through the water pipe. The water pipe is galvanized, but it looks a little deeper. It is connected with plastic. In very dry soil, the short galvanized layer is close to the surface. A real ground rod went in quickly.
All of the above happened in the 70s. But this is not unheard of. The KBR in Iraq did some poor quality work, which resulted in the deaths of about 18 American soldiers. Damn it's almost the same situation, there really is no excuse.
http://www.nytimes.com/2009/01/23/washington/23electrocute.html
By the way, we are still married :)
In Afghanistan, I often find the wiring is terrible. We live in a modified steel container, and the camp is powered by a generator. Without grounding, when there is water on the ground, if you touch the outside of the transport container (your feet are on the wet ground), you will receive a severe electric shock. I took out a multimeter and found that the voltage from the container to the ground was 115 volts! Fortunately I solved this problem and no one is worse than a bad "bite".
Another anecdote: My antenna was disconnected from the radio and the coaxial cable was hanging on the wall. We experienced a sandstorm and generated so much static electricity that there was continuous arc jumping from the conductor to the barrel of the UHF connector. This is why military-grade products have strict protection circuits.
Dude, I didn't think of the static electricity of the sandstorm. Glad to know:) My BiL has some stories about the container that lives there and the electrical problems he faces, but the main ones are ground loop problems and power failures. That place is dangerous everywhere, haha.
Another note about grounding the neutral wire. Someone pointed out that the isolated area is used in hospitals and other places. Another important place where the ground is not connected to the neutral line is in the sub-panels (i.e. garages, attachments). In this case, the circuit breaker panel will have 2 busbars, one for neutral and one for grounding. They should not be connected.
The reason for this is that if the neutral wire returned to the main board is damaged, the final result will be safe (the sub-panel is not powered). If the neutral wire and ground are joined at the sub-panel and the neutral wire connection is cut off, all current will pass through the ground wire The bearer will most likely not be detected.
This is why the subunit should have an RCD.
In the United States, the ground wire and the neutral wire (ground wire and ground wire) can only be connected near the service entrance. Anywhere inside, the neutral and ground wires should be separate. This helps prevent ground loops and potential accidental voltage differences from becoming too weird.
This is also true in the UK and most parts of the world.
(I think the first paragraph should make it clearer that it is the method used in the United States and Canada, while other countries may have very different grounding management methods...not everyone uses the TN-CS system)
Fascinating article. Why do 22Kv to 19Kv step down? I am not criticizing, I just don't understand. Apart from providing isolation, this seems almost meaningless, but I am sure I don't see the big picture.
This is actually a kind of sublimation! The 22kV phase-to-phase voltage is 12.7kV to neutral/ground voltage. 19kV and 33kV (phase to phase) have the same voltage relative to the ground, which is a common transmission voltage.
Therefore, it is almost certain that they are allowed to use the same insulators, fuses, switches, etc. as in the 33kV system.
The permitted SWER voltages (in Australia) are 11, 12.7 and 19kV. [AS 2558-2006 Australian Standard™ Transformer for Single Wire Ground Loop Distribution System]
Edit: Oops, correction: it is not a step-up transformer, the primary is connected in phases.
I was working in Greece a few years ago and we installed a box on the transformer pole. It stopped working. After further investigation, they scratched the transformer. The box, originally worth 20 times as much as a transformer, was left neatly on the grass
A naval partner from the Philippines works for a power company there. He told me that they found a copper thief at the end of a single tap for several miles. Starting from the main line, he cut the ground wire with an axe and yanked the copper wire down. At the end of the faucet, there is no ground wire, and the neutral wire becomes a huge transformer. They found the guy dead next to a pile of coiled wires, holding the last cut ground wire in his hand.
I used to use huge analog mixing desks (think 96 channels) for professional studios. As part of the customer acceptance test, the desk will be set in the factory, and the engineer will check whether the noise is within the specifications. It turns out that good grounding is essential for good performance, so we have a section of welding cable connected to a copper rod, and the copper rod is thrown into the stream behind. But in summer, the creek dries up, the ground resistance increases, and the noise level increases, so the test failed. So on the way back from the bar, everyone will pee on the ground rod. The acceptance engineer thought it was interesting. This is a good excuse to drink at lunch time.
Realize that high-voltage transformers are very dangerous. Even a well-trained engineer can set up the system incorrectly. Remember, you should try not to get your project into a death trap by removing a wire. I have seen PE use operators to connect transformers to ground in ungrounded systems. There is a break in the grounding wire, one side of your wire goes through the transformer, and the other side is grounded. Pay attention to safety and don't worry. While ensuring the safety of the system, consider all possible wire disconnections.
@ Annie In the United States, NEC requires that even the kitchen of a one-bedroom house has 2 20 A. Small appliance circuits, so the kitchen circuit is separated from other circuits or should be separated from other circuits, perhaps except for kitchen lighting.
For SWER systems, the ground loop is different from the neutral on the secondary side of the service transformer. When the mobile house leaves the factory, the ground bus is not connected to the neutral bus. Because there are some places in the United States that do not use grounded neutral conductors. If a mobile device is connected to such a system, the mobile home will become the grounding point for every household that shares the transformer secondary with it.
My house has a granary and corn dryer with 3-phase 220 settings. Every few years, they have to replace the service box because one of the legs will rust. I asked one of my electrician teachers and he suggested that it should be short-circuited to ground at some point. When I made a suggestion, my family looked at me in disbelief. (More about downtime/cost issues.)
However, when my cousin had to redo the motor controller, he found that the mouse had bitten the wire in the gooseneck. The box and wires were too old and corroded, and the fuse did not pop out.
Considering the electrical mess, I was surprised that no one was killed.
This will definitely cause problems!
In the "Handling Faults" post above, if a short circuit or failure occurs between the utility transformer and the circuit breaker panel (upstream), what will happen to the customer's electrical appliances?
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