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I recently installed a solar inverter in my house and learned that earth must be connected to neutral. I am very puzzled by this, since AC changes direction of current flow, so according to me, there is no real "neutral". If the sine wave is at the bottom of the graph, neutral will be live? In that case current will flow in the other direction.

How can it be that neutral will always be 0 volts if there is no current flowing through the system? I tried asking people, but the only answer I got was "there is a feed" which is your live. But what happens if the AC wave goes below 0 volts? In that case you will shock on earth.

I have played with electronics my whole life, but when I learned this fact, at first, I didn't want to believe it.

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  • \$\begingroup\$ By connecting neutral to ground there still is a potential difference between the two wires. It is about that difference. \$\endgroup\$
    – RemyHx
    Nov 29, 2022 at 5:59
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    \$\begingroup\$ To be clear, there IS current flowing in the 'neutral' wire. In fact, it's the EXACT SAME amount of current flowing in the 'live' wire. Consider: GFCI devices don't sense short circuits, they sense when the amount of current on the live is different from the current on the neutral (and if so, it may be flowing through YOU), and then they trip. Somewhere around 10mA is enough imbalance to do it. \$\endgroup\$
    – Kyle B
    Nov 29, 2022 at 7:17
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    \$\begingroup\$ Do you have any problem connecting a battery negative terminal to ground? Do you have any problem connecting battery positive to ground? \$\endgroup\$
    – Andy aka
    Nov 29, 2022 at 9:51
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    \$\begingroup\$ Why do you think that if the sine wave is at the bottom of the graph, neutral will be live? And why do you think that if the AC wave goes below 0 V, then you'll get a shock from the earth? I can tell that you have some misconception that's leading you to these false conclusions, but I can't tell what that misconception actually is. \$\endgroup\$ Nov 29, 2022 at 10:36

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In any utility supply, the neutral is the terminal that is earthed.

In the three phase supply shown below, the neutral is the star point that is earthed.

enter image description here

The line-to-line voltage is 400 V and the line-to-neutral voltage is 230 V.

A person, standing barefoot and touching the neutral terminal, will not experience an electrical shock since neutral and earth (being tied together) are at the same potential.

Then again, a person standing barefoot and touching a line terminal will experience only a 230 V electrical shock.

Likewise, in the single phase inverter shown below, the neutral terminal is the one that is earthed.

enter image description here

Contact with the neutral terminal of the inverter, whilst being barefoot, will not result in an electrical shock.

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You have a misconception here, and that misconception is causing you to falsely believe that if the white wire from the inverter is earthed, then the white wire will sometimes be live and the earth will sometimes shock you.

The cure for your illness is to fix that misconception. Unfortunately, from your question, I'm not able to tell what your misconception actually is.

Maybe your reasoning is something like the below. Please note, by the way, that every sentence in the below paragraph is false.

With an AC power source, half of the time, the black wire is energized, and half of the time, the white wire is energized. Therefore, if you connect the white wire to earth, then the earth will be energized half of the time. Touching something that's energized will shock you. Therefore, if the white wire is connected to earth, then touching the earth will shock you.

The truth is that the inverter will not energize the black wire half of the time and the white wire half of the time. What is true is that half of the time, the black wire has a higher potential than the white wire, and half of the time, the white wire has a higher potential than the black wire. However, "higher potential" doesn't necessarily mean "energized." If we can somehow force the white wire to be at ground potential (which is safe to touch), then what will happen is that the black wire is sometimes above ground potential (which makes it dangerous to touch) and sometimes below ground potential (which also makes it dangerous to touch).

Well, "somehow forcing the white wire to be at ground potential" is exactly what connecting the white wire to the earth does. When the white wire is connected to the earth, a tiny amount of current flows through that connection and causes the white wire to stay at ground potential at all times.

No significant amount of current will actually flow through the earth, because current only flows in loops, and there's no complete loop there.

Assuming that the soil is conductive and there isn't a lot of current going through it, touching the soil all by itself and nothing else will never shock you. You only get a shock if you touch two substantially different potentials, and the soil obviously can't have a substantially different potential than itself.

(However, if the soil has high resistance, or if it somehow has a lot of current going through it, then two parts of the soil can have substantially different potentials, and so touching the soil potentially could shock you.)

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  • \$\begingroup\$ +1 for "every sentence in the below paragraph is false" \$\endgroup\$
    – BrtH
    Nov 29, 2022 at 17:12
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    \$\begingroup\$ Re, "if it somehow has a lot of current..." Every so often, you'll see pictures like this one in the news. Cows cluster under a tree, seeking shelter from a storm, Lightning strikes the tree, Immense current radiating away from the base of the tree over the surface of the ground creates enough voltage gradient to allow a lethal fraction of the current to run up one leg of a cow, through it's torso, and down another leg. All fall down. \$\endgroup\$ Nov 29, 2022 at 20:56
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    \$\begingroup\$ @SolomonSlow if only those cows had known about positioning their legs along an equipotential line, or balancing on one leg... \$\endgroup\$
    – P2000
    Nov 30, 2022 at 5:33
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  1. Voltage is always a measurement between 2 points. We say that Neutral is 0V because it's the reference point we use to measure other voltages in the system - so naturally if we measure from Neutral to Neutral, we measure 0V.
  2. Terminology: we don't "connect the Neutral to Earth", we define the Neutral conductor as the conductor which has been connected to Earth. It's subtle, but there is a difference. If there is no Earth connection, then there is no Neutral. As above, you can still choose one wire as the 0V reference by which to make other measurements, but you won't be measuring against Neutral, because of it's not Earthed, it's not Neutral.
  3. Yes, the AC voltage and current changes direction 50 or 60 times a second (depending on where in the works you are), but why do you think this would be a problem for Neutral being 0V? We've defined Neutral as 0V so that we have a reference to be able to measure other things. If Neutral were not 0V, how would we know if Live/Line was positive or negative?
  4. Current always flows in a loop. Always! Neutral being 0V does not mean that there's no current flowing in it. Whatever current flows "out" of the Live/Line wire, that same current is returning through the Neutral wire (for a single phase system).
  5. You're never "shocking the Earth", because there's never any current flowing through the Earth (in a properly functioning system). If something goes wrong (like your Neutral wire breaks) and you do end up returning current through the actual Earth back to your local distribution transformer, then you'll notice some weird behavior from (and possibly damage to) electrical appliances in your house because sand & rocks & mud & dirt don't conduct nearly as well as copper or alumin(i)um wires do.
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I think you are a bit confused what an AC voltage is and how it works...

So first: how do we measuse a Voltage? We always have to connect two leads. We define one as the reference and measure the potential difference of the other one to this reference.

So if you have a single 5VDC source you can't say if it's +5V or -5V as long as the reference is not defined. The only thing you can say that the coltage difference between the two leads is 5V. What your Voltmeter shows (plus or minus) depends on how you connect it.

Only if we define the - lead as the reference, we can say, we have a +5V source.

From a measurment point of view the only thing we do by connecting Neutral to GND is that we reference it. Now we can measure the phase against a known (GND) potential.

This connection has benefits and downsides in practice, but it's just the way it is.

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