can some one explain earth to me??? - Page 1
Forum section: electronics / beginners

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: January 30, 2015, 12:20:16 pm
content: hi everyone!i am 14 and i don really understand earth (not the planet, earth/ground if there the same). i know that its your friend and things in metal cases have to be earthed otherwise you will get a shock.so could someone try to explain very basically what earth is that would be much appreciated.thanks in advance!(PS dont be to harsh i have not been into electronics for long)

author: necessaryevil
author_rank: Regular Contributor
timestamp: January 30, 2015, 12:49:31 pm
content: Well, it is an alternative return path for electrical current. An electrical tension can only exist between two points and current can only flow in a "closed circuit", which means the power source and the device together with the wiring need to make up a closed loop.On power grid installations, one of the points is connected to the soil and is defined as 0 volt. This is called the ground, neutral, or whatever (I can be technically wrong, english isn't my first language and it could be different in US/UK/Australian english).The earth which you are referring to is called the protective earth. It is an alternative and short path to the gound/neutral. It could be viewed as an overflow drain (is this what it's called?) in your kitchen which prevens your whole house from flooding when your washer (or a water pipe) breaks down.The protective earth must have different wiring (in your house) than the neutral/0, because the large currents in the neutral conductor can cause stray voltage - which just means that the neutral conductor is not a guaranteed 0v. This is why the neutral conductor should NEVER be connected with the earth (again, in your house, in a powerplant they are connected)

author: Skimask
author_rank: Super Contributor
timestamp: January 30, 2015, 01:05:41 pm
content: http://lmgtfy.com/?q=earth+ground

author: klr5205
author_rank: Regular Contributor
timestamp: January 30, 2015, 01:07:10 pm
content: Put even more simply, "ground" is just a point of reference. It is an agreement that whatever spot you choose to call "ground" in your schematic will be 0V, with all other voltages measured with respect to it.The image below shows how you can define ground to be wherever you want without affecting anything:Earth, on the other hand is exactly that: An electrical connection to the earth. It's generally used as a safe path for current to flow in in the event of some kind of fault. For example, if somehow a hot wire in your properly earthed metal chassis were to contact the side of the enclosure, a large current would flow until your breaker trips. However, if your enclosure were not earthed and the same thing happened, the enclosure would just be sitting there at mains potential waiting for you to touch it and get an unexpected shock!

author: Howardlong
author_rank: Super Contributor
timestamp: January 30, 2015, 01:32:58 pm
content: On mains wiring, depending on your national wiring code and locale, sometimes the earth bonding point with neutral can be quite some way away.What this means is that the neutral and earth may have induced currents, perhaps only a volt or two, (mine's 1.3V) but lots of current, so several watts. It's perfectly feasible to use that power, by, for example putting it into a step-up transformer. As it doesn't go through your electricity meter, it doesn't cost a penny, just don't tell the Free Energy folk that!

author: AndreasF
author_rank: Frequent Contributor
timestamp: January 30, 2015, 03:00:22 pm
content: Quote from: Howardlong on January 30, 2015, 01:32:58 pmInteresting! But wouldn't the inductive coupling also cause current to flow in the "live" wire once you put a load between neural and earth, since it's effectively the primary side of an isolation transformer?

author: DrMag
author_rank: Regular Contributor
timestamp: January 30, 2015, 07:03:22 pm
content: One of the reasons we like to use earth as a ground reference is because of the size of the planet. When you draw a current, it creates a slight imbalance in the distribution of electrons locally. Ideally, you don't want your ground reference charging up (it's a headache in spacecraft applications, for example), so an ideal ground reference is one that can source a lot of electrons without significantly changing its own electrical potential. The earth is big, and the ground around us is conductive, so it works very well.Of course, it also leads to localized charging that result in lightning strikes, but that's probably another discussion. =)

author: Jeroen3
author_rank: Super Contributor
timestamp: January 30, 2015, 09:48:24 pm
content: I'lltry...Typically any appliance connected to an AC-grid will have neutral == earth. Not having any, directly or indirectly was prohibited ages ago (1920?) because it is dangerous.Any typical AC-grid will have 4 conductors and earth.You'll have 3 AC-phases, Neutral and Earth. The wires going to your house will be 1 of the phases, and Neutral. You house has it's own earth pin pushed firmly into the ground, and wires from there because you don't have soil on the first floor.Search forstar-wyeon google.The voltage will be generated over the generator stator coils, and instead of being kept at a floating potential relative to earth, it is referenced to earth directly at the source. By connecting earth & neutral.This is to prevent the potential equalizing currents* running through the appliances parasitic resistances and/or you because you're on earth and touching the appliance.Generators require lots of equalizing current, more than the few nA/uA your lab supply does.*Current required to get two nets at the same voltage.Neutral will also be electrically connected to earth using a current shunt. If any current is running through this shunt that means somewhere current is not following intended wired Phase-Neutral (or phase-phase) path and so there must be a leak somewhere. If this current gets too high, the generator will be disconnected from the grid to prevent stuff from burning out. Neutral and Earth are never disconnected.Actually, the above isn't true. There are multiple transformers between you and the generator. Since the generator may well be a few Kilo Volts.Variations on the transformer wiring exist, I don't know about Australia. At least one of the transformer secondaries will become a new Neutral, and thus be 0 Volt to earth.There is this wiki that might help youhttp://en.wikipedia.org/wiki/Ground_and_neutral.

author: Howardlong
author_rank: Super Contributor
timestamp: January 31, 2015, 01:45:37 am
content: Quote from: AndreasF on January 30, 2015, 03:00:22 pmIt depends where you neutral/earth bond is. I don't pretend to be an expert, It's probably 35 odd years ago that I was "educated" by my physics teacher in this feature, but almost all of that is going to be induced on the "other" side of the meter if your bond is only at the utility's site, and not locally, so it won't be metered. In the UK, some installations do have an earth bond at both the utility and the premises, so of course it wouldn't work in that situation.Thinking about it, I'm not sure it's all induced current: there can also be voltage drop between the utility and the premises due to resistance in the wiring combined with load. If it's induced, the voltage should be a fairly constant value over time. The resistively created voltage component will be variable based on combined load over the distribution network.

author: Nerull
author_rank: Frequent Contributor
timestamp: January 31, 2015, 03:53:39 am
content: US electrical code requires a local earth-neutral bond, so it would almost never work here, except in some older buildings.

author: xibalban
author_rank: Regular Contributor
timestamp: January 31, 2015, 07:24:43 am
content: I always thought of "earth" as being the universally adopted and absolute 0 Volt reference.You see, since voltage (or electric potential) at a point is always measured by comparing it to another voltage somewhere else, there is a need for one universal and absolute voltage level where everyone in the world could reference from, hence the "earth" i.e. the point of absolute 0 Volt.Also, since the generating station (or substations) of our power system connect the neutral with earth, the earth does provide a low resistance path for mains circuits.A fun fact:If you connect a 220V/220V transformer (yes whose input is equal to output), to your mains then you have effectively isolated the neutral-earth connection of the power system. In other words, you'd not receive any electrical shock from the output terminals since earth is no longer the return path to complete the circuitMy $0.002

author: helius
author_rank: Super Contributor
timestamp: January 31, 2015, 07:38:10 am
content: But the existence of earth currents (and geomagnetic fields) means that the earth isn't at the same potential everywhere. But as the accessible conductor with the most mobile charges, it's useful as a "universal drain"Ground/earth is also very important for RF signals, since antennas need a ground plane.

author: Howardlong
author_rank: Super Contributor
timestamp: January 31, 2015, 08:54:09 am
content: Quote from: helius on January 31, 2015, 07:38:10 amIt depends on the antenna. A dipole, for example, needs no ground plane.In addition, those antennas that do have "ground planes" don't have to have that ground plane physically connected to earth, it can be done with floating radials of appropriate size.

author: Muttley Snickers
author_rank: Unknown
timestamp: January 31, 2015, 09:10:41 am
content: Greeting's All,Whilst we are on this subject if I may indulge my curiosity.In regards to Earth potential difference which we have to takeinto account in larger systems that we install and maintain.I fully understand that this could be just another " piece of string "question but any thoughts on approximate measured voltage andavailable currents should one have a ridiculously long set of Flukeleads, say 5 or 10 Km's for impracticality sake and probe the earth.For indulgence sake we would exclude the leads resistance.I have read many manuals on avoiding Earth potential difference,but what if in the quest for knowledge I actually want some of it.Muttley

author: tggzzz
author_rank: Super Contributor
timestamp: January 31, 2015, 09:23:31 am
content: Quote from: Muttley Snickers on January 31, 2015, 09:10:41 amAre lightning strikes involved?If so you don't have to go more than a few yards to get large potential differences. Inches in the worst case, hence the advice to keep your feet together if you feel your hair standing on end.OTOH "earth"insideequipment (especially RF equipment) is largely a fiction, Here the term earth should not be used; "chassis" or "common" are better terms.This is far more information than the OP needs at this stage, but it can prime them to gradually gain further understanding over the years: "the concept of earth is a fiction, but in some circumstances there are useful approximations". The key point, as the OP clearly does realise, iswhatare the required properties of earth and/orwhyis there an earth and/orhowdoes the earth work (or otherwise).

author: Muttley Snickers
author_rank: Unknown
timestamp: January 31, 2015, 09:37:48 am
content: Are lightning strikes involvedNo, it's a nice sunny day, hypothetically.Muttley

author: electr_peter
author_rank: Unknown
timestamp: January 31, 2015, 10:54:29 am
content: Muttley,If you stick DMM probes in earth few cm (or few m) apart and measure large AC/DC voltage, run awayEarth represents 2 dimensional (or 3 dimensional) resistance grid, which has unexpected properties when compared to simple one dimensional resistance model (i.e. wires). This topic is important in context of mains power distribution and earthing in urban/rural/residential/industrial/marina areas.

author: tggzzz
author_rank: Super Contributor
timestamp: January 31, 2015, 11:09:06 am
content: Quote from: Muttley Snickers on January 31, 2015, 09:37:48 amAh, that's insufficient I'm afraidFamously Thishttp://news.bbc.co.uk/1/hi/uk/558095.stmoccurred nowhere near a cloud. If you fly in a 787, then be thankful for the lessons learned from that!

author: Muttley Snickers
author_rank: Unknown
timestamp: January 31, 2015, 11:15:21 am
content: I hope that I am not to far off topic in asking this question.All of our reference material is focused on the non introductionof earth loops and isolation of common conductive links betweenremote building's via opto isolation or open ended shields.I have been called to jobs in the past were devices and systemshave been destroyed because the previous installer did not seethat common connection of remote modules is not the donething for good reason.This is not a quest for free energy, we are not going back there.Many Thank'sMuttley

author: electr_peter
author_rank: Unknown
timestamp: January 31, 2015, 12:26:24 pm
content: Quote from: Muttley Snickers on January 31, 2015, 11:15:21 amElectrician: "I see unconnected terminal, it must be connected."Owner: "Why?"Electrician: "Because it is unconnected..."

author: tggzzz
author_rank: Super Contributor
timestamp: January 31, 2015, 12:38:07 pm
content: Quote from: Muttley Snickers on January 31, 2015, 09:37:48 amOr you can consider geomagnetic solar storms, which have had unpleasant effects as a result of the non-ideal properties of the earth (earth in both senses, of course!).

author: Muttley Snickers
author_rank: Unknown
timestamp: January 31, 2015, 12:49:04 pm
content: This silly smart TV restrict's me from staying logged in.Surprisingly E14/ Farnell dont carry 5 or 10 Km Fluke testleads with zero resistance, that now buggers me right up.Muttley

author: Lesterwyatt
author_rank: Regular Contributor
timestamp: January 31, 2015, 05:30:34 pm
content: Quote from: necessaryevil on January 30, 2015, 12:49:31 pmThis in not entirely true in the UK. In the UK we have several earthing systems one of which is called TNCS or PME.In this system the protective earthing conductor of an installation is connected to the neutral terminal supply side.from this point on every 40 meters or so there will be a earth electrode taken from the neutral until supply transformer where the star point will be earthed. This system guarantees a low impedance to earth typically 0.35 ohms or lower.There is however precautions to take when earthing a PME installation as a whole. The installer has to make sure that all conductive parts (extraneous) are earthed at the same potential, this includes mains water pipes gas and oil pipes. In the unfortunate event that the neutral conductor became open circuit, you would have 230V running through the installation protective conductor, and thus the installation extraneous conductive parts. Also care should be taken in shed installations of a PME system. If lets say you have a 40M run to a shed and the last earth electrode on a distribution network is 40M prior the service cable entering the property. Because of the long distance from last electrode there would be a possible potential difference between you at shed and the earthing system under fault conditions. You can get around this problem by installing an electrode at shed and referencing the shed at this potential (TT system).In electrical instillation's earthing is the most misunderstood subject, it has two main objectives:1. It keeps conductive parts at the same potential, this is so you don't get killed when your touching your kettle and your tap under fault conditions.2. It gives fault currents a low impedance path to earth, this will make sure your circuit breaker will disconnect in the required time (0.2 sec) .Also there is functional earthing, but i won't go in to that.LesterI

author: Nerull
author_rank: Frequent Contributor
timestamp: January 31, 2015, 09:28:11 pm
content: Quote from: necessaryevil on January 30, 2015, 12:49:31 pmA statement contradicted by the electrical code of many countries.

author: SeanB
author_rank: Super Contributor
timestamp: February 01, 2015, 06:27:00 am
content: Neutral and PE are never connected in the house, only at the utility side where they are connected on the supply side of the electricity meter, along with an earth rod connection and bonding to water piping if metal. Inside they are required to be separate. Often they will be separate all the way back to a substation transformer bonding bus, which can be 200mm2 copper bar.

author: aveekbh
author_rank: Regular Contributor
timestamp: February 01, 2015, 06:49:42 am
content: Quote from: rickselectricalprojects on January 30, 2015, 12:20:16 pmThis is how I understand it. The earthing system serves two purposes:In any mains-connected equipment, all exposed metal (i.e., the chassis) needs to be earthed. This ensures that any conductive surface is always at 0 volts. Thus, if you touch the metal, your hands and feet are at the same electrical potential, and you will not receive a shock.Should the chassis come into contact with live voltages, any shock can be fatal. Because the chassis is electrically connected to earth through a wire, a large current would flow through the earth connection. This should be enough to cause safety mechanisms to activate - fuses would blow or circuit breakers will trip - cutting off the supply, and keeping people safe.Please feel free to correct me if I'm wrong.There are various ways in which the earth connection can be provided. This video will give you an idea about the systems in use in the UK, but the principles are the same everywhere.These days, one should also have a residual current device which will also disconnect the supply if there is an abnormal condition. These are an additional safety feature, and should also be used in conjunction with fuses or circuit breakers.Hope this helps

author: c4757p
author_rank: Super Contributor
timestamp: February 01, 2015, 06:53:00 am
content: Quote from: SeanB on February 01, 2015, 06:27:00 amAgain, depends on the country. The US has nearly one transformer per house, so we do things a bit differently.