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    protective earth neutral

    sorry for a dumb question......

    But at the Mains supply service panel, the Earth and Neutral wires are connected together.

    So why bother taking Earth, Live and Neutral to a 3-wire offline SMPS?

    Earth and Neutral are connected together.

    Why not just connect up Live and Earth
    OR... Live and Neutral

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    neutral and earth

    The Neutral is connected to a metal plate buried in the Earth at the Transmitting Station.

    The Earth is connected to a metal plate buried near the point of usage.

    The Neutral is used to provide a reference to the Line Supply.
    The Earth is to protect the Equipment by connecting it to ground potential that is same as the usage so potential difference between the user and the Equipment is low if not zero in case of failure.

    I have never heard of Earth connected together with Neutral as Neutral comes from the Transformer.

    Hope this helps.



    •   Alt26th April 2009, 17:47

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    earth live neutral

    I am pretty sure that at the transformer sub-station that exists just before a domestic property, the neutral is connected to Earth.

    That is, the Neutral, at the SECONDARY of this transformer, is connected to earth ?



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    earth neutral fault

    Different earthing arrangements have been used thrue the history of electrical power, and different ones are in still in use today. They have different implications regarding electrical safety. Apart from general accepted IEC regulations, additional national rules are in effect. For a general terminology and explanation, see http://en.wikipedia.org/wiki/Earthing_system



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    connect live neutral and earth

    as can be seen here

    http://www2.theiet.org/Publish/WireR...s_answered.pdf

    ...figure 1, top of second page...This is the most common TN-S system ........earth and neutral are connected together.........they are the SAME node.

    so why are they BOTH taken to an equipment?

    they are the same node, and surely we should only take one of them to an equipment -surely?



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    why earth to neutral

    An electrical engineer should know the answer since his study! In a short, you have to guarantee, that the PE connector provides a reliable earth connection and can't carry a dangerous voltage in all cases of broken wires, short circuit and overload.

    Thus, the PE (protective earth) must be separated from neutral in the installation and isn't allowed to carry load current, while neutral must be isolated against accidental contact as good as live.

    You can surely figure it out yourself, when you consider different cases of failure. See IEC 364-4-41 Protection against electric shock for respective regulations.



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    where should neutral connects to earth ground

    If you understand why the Earth & Neutral is connected at the transformer and at POA of the premises, you should also understand why we run A, N & PE to all points!

    A & N are PHASES supplying current to the circuit, PE is for Protective Earth under fault.

    The Neutral "should" be at Earth Potential, but under different conditions this isn't always so. Think of faults and also three phase transformers, wired star, with harmonics and unbalanced loads.

    Think about the potential (pun intended) combination of current paths under different fault conditions, especially when Human contact is involved.



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    multiple earth neutral connection

    OK, the thing is, The Earth connection foxes me out because mainland Europe do perfectly well without any Earth connections to their domestic goods.

    I dont understand why we in UK need it (Earth connection) when in mainland Europe they don't



    •   Alt28th April 2009, 19:24

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    tn-c rules earthing

    I don't see, that UK has different safety regulations. There are apparently different habits.



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    difference between earth and protective earth

    i realised that the reason for using earth as a reference in the power grid was because if a mains connected electrical apparatus suffers physical damage such that the live connection touches the metal outer casing, then a large current would flow to earth and blow the fuse.

    this would de-activate the equipment so that if a human touched the damaged equipment with two hands, then a large shock current would not flow through the person's heart and kill them, since the fuse had blown.

    the other reason for earthing as i know it, is for electrical noise filtering....where common mode noise is filtered to earth.
    -This is seen if you build a crystal AM radio, and it usually wont work till you earth the reference by directly connecting it to earth ground.......it desnt work due to noise "killing" out the small RF signal.



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    live and neutral together

    Hi!

    There is only one exception where Neutral/Earth are common, and that is the T-N-CS system, formerly called Protective Multiple Earthing, often utilised in rural areas where clay/sandy soils that don't provide efficent ground earthing are found!

    T-N-CS/PME has to be specially authorised because it is extremely dangerous if the combined earth/neutral conductor develops a fault or high-resistance, and the Supply Authorities are obliged to put a warning notice at the supply terminals when PME is in use.

    Even so, when T-N-CS/PME ***is*** in use, the Live, Neutral & Earth Conductors ***must still*** be separately connected to the final
    appliances/consumer loads, and the Supply Authority will supply a separate Earth Connecting point at the meter inlet!

    Hope this helps!

    Chris Williams



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    Re: Earth and Neutral are connected together

    I'm in the UK.

    The reason why some devices need an earth and some do not is because of the types of internal isolation they have. An earth is necessary if there is any chance of an exposed conductive part touching the user or an external connection being attached (headphone socket for example). If all the 'live' or potentially live points are out of reach, for example inside a TV cabinet, the earth is not necessary.

    Where it IS possible to touch conductive parts, it is still possible to use equipment without an earth provided it is 'double isolated' which means there are at least two barriers between the incoming power and exposed parts. Equipment designed this way should bear a symbol which is two concentric squares and it will normally have been tested to high voltage ( >1.5KV) to ensure no conduction can take place. Usually, the double barrier is a transformer where the primary and secondary windings share the same core but cannot come into contact with each other.

    An earth IS used wherever there is a risk of electric shock by direct connection to incoming AC or by build up of charge through capacitive leakage. The idea is that should a component failure occur or conductive path be made, the current will flow via the earth connection and operate the safety trip in the fuse board. If the fuse board has earth leakage trips, they will detect the current and switch the power off, if it has balanced trips, it will detect the line and neutral are carrying different currents and turn it off, either way you are protected.

    Brian.



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    Re: Earth and Neutral are connected together

    Sorry to re-initiate this thread. But I was going through and am not sure I completely understood. I don't mean to piss anyone off (seriously) with what is a easy and fundamental concept to many. But I don't see how eem2am 's question has been answered. I am still confused as to how A and N are PHASE when Neutral is connected to ground. From the image trekkytekky provided I tend to thing that the Neutral wire, though connected to ground potential (like Earth) isn't connected to the conducting frame of the appliance and device, and that is why it needs another wre (Earth) to connect it to ground potential?

    Maybe someone can answer this by clearing: Why Neutral and Earth are required when the two are "shorted" at the station? Doesn't that make them one point. Eem2am, if you understood it yourself, I would appreciate it if you explained it.

    Thanks.



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    Re: Earth and Neutral are connected together

    The reason is that Earth as connected to the conducting frame (Chassis) of equipment should remain at or close to zero potential at all times. If you take a worst case scenario, the phase and neutral shorted directly together, until fuses blow somewhere, there would be equal resistance back to the transformer on the phase and neutral wires so it would adopt half the AC potential at the point of shorting.

    Take a real example, here at home I have a 440V 3-phase feed directly to the transformer (substation) with 200A fuses in each of the phase wires. On occasions in storms the wires, which arrive overhead on poles, have shorted together. The N wire rises to about 100V AC above earth potential. If I used N as the chassis it would be dangerous to touch but the Earth which isn't carrying a return current would still be at zero and quite safe. Although I have 3-phase feed which is unusual for domestic use, the same still applies to a normal single phase connection.

    Please don't ask why I have an industrial power feed to a small four room house - it's for historical reasons, the overhead cables used to go to other places which no longer exist, the supply was just left as it was.

    Brian.


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    Re: Earth and Neutral are connected together

    "On occasions in storms the wires, which arrive overhead on poles, have shorted together. The N wire rises to about 100V AC above earth potential. If I used N as the chassis it would be dangerous to touch but the Earth which isn't carrying a return current would still be at zero and quite safe"

    Just to make sure I understood: If the Phase and Neutral are shorted the Neutral is no longer at ground potential - so using it as a ground is dangerous.

    The Neutral still connected to ground at the station though right? But along the transmission lines its also been shorted (for some reason) to the phase wire - result is that Neutral is no longer at ground potential, so for a device at home, a nearby ground potential is required and that is connected by the Earth wire, which is connected to the chassis. Have I got it right?



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    Re: Earth and Neutral are connected together

    I'm trying to fathom that statement but I think it's right. What I meant was if a fault occurred, maybe elsewhere in the network in a different building and a lot of current flowed down the neutral wire, it's resistance and inductance would cause a voltage to be dropped along it. Worst case would be a direct phase to neutral short circuit which would look like two low value resistors (the phase wire and the neutral wire) connected across the AC source at the transformer. So the voltage would be about half the transformer voltage. The Earth wire would not be carrying that current so it would still be at or close to zero volts and therefore safe. Basically, the idea is to keep the power carrying wires and the safety wire apart. Of course it is possible for current to flow to the Earth wire if a fault happens but in that case one of two things should happen: the Earth current should operate the Earth leakage trip or the imbalance in phase and neutral currents should operate the RCB trip.

    Brian.



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    Re: neutral and earth

    Quote Originally Posted by maheshkuruganti View Post
    The Neutral is connected to a metal plate buried in the Earth at the Transmitting Station.

    The Earth is connected to a metal plate buried near the point of usage.

    The Neutral is used to provide a reference to the Line Supply.
    The Earth is to protect the Equipment by connecting it to ground potential that is same as the usage so potential difference between the user and the Equipment is low if not zero in case of failure.

    I have never heard of Earth connected together with Neutral as Neutral comes from the Transformer.

    Hope this helps.
    neutral is not buried anywhere as far as i know...in many cases neutral wire is connected to earth to remove space charges from earth conductor..Neutral wire is tapped and that tap is earthed,but the neutral wire itself is not buried.
    Last edited by rambleach; 20th April 2012 at 17:46.


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