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I live in a house where each socket has 3 connections,:

  1. hot (phase)
  2. neutral
  3. ground

Where:

  • The voltage between hot and neutral is about 220V AC.
  • The voltage between ground and neutral is about 2-3V AC.

Can I use those 2-3V as a 'free' (not paying for it) power source? Do you know any project using them?

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    \$\begingroup\$ That's not free power. Repeat after me: there's no free power. There's no free power. Anyone talking about free power on youtube is trying to sell me something. There's no free power. \$\endgroup\$ Commented Apr 26, 2020 at 10:50
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    \$\begingroup\$ Ok @MarcusMüller, not 'free energy', but 'energy without paying for it' \$\endgroup\$
    – Tasossssss
    Commented Apr 26, 2020 at 10:52
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    \$\begingroup\$ No, if you consume energy after the meter, you will pay for it. \$\endgroup\$
    – Justme
    Commented Apr 26, 2020 at 10:54
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    \$\begingroup\$ @Tasossssss no, it's not energy without paying for it. See my answer. \$\endgroup\$ Commented Apr 26, 2020 at 10:58
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    \$\begingroup\$ @KingDuken "Not "free energy", but "energy without paying for it"" \$\endgroup\$ Commented Apr 26, 2020 at 20:20

4 Answers 4

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Short answer: Kirchhoff current law says... no. That ‘free’ current makes its way back to the utility feed, through the meter, and back to the pole, along with all the other currents in your house.

Long answer: in the video, they’re using the voltage difference between neutral and ground at the plug. This is caused by I-R drop on the neutral wire carrying the return current back to the panel. There’s a corresponding I-R drop on the hot wire, which you could see if you were to measure the hot voltage directly from the panel to the receptacle. You will only see this if there is a load on the circuit feeding the receptacle. Otherwise it won’t be there.

Here’s the thing: neutral and ground are tied together at the panel. All that’s happening in the video is that some of the neutral current is being shunted back to the panel via the ground wire. But make no mistake: it still makes its way back to the panel, through the meter, and to the utility. And the meter will see it and tally it. So it’s not ‘free’ as in beer at all.

(Don’t ever connect neutral to ground at the socket. It defeats the safety function of the ground wire, which normally never carries current.)


Now, about that I-R drop. 2-3V is an acceptable neutral drop per electrical codes, so there’s no need to ‘fix’ it. If it were more than that, it would be time to call an electrician to fix the faulty neutral, which he or she would do by making the run shorter, installing a new run, using thicker wires, or converting the run to use higher voltage.

The latter ‘fix’ is why some runs in a US home are 240V (dryer, oven, A/C) while normal plugs are 120V. Using higher voltage reduces wire loss for these high-power devices, so in that sense it’s ‘free’.

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  • \$\begingroup\$ I think the voltage differential would draw very little current. Causing no heat. Now, since it's alternative current, it's another story. When neutral is high, the current potential is probably far higher. And voltage too. \$\endgroup\$
    – Fredled
    Commented Apr 26, 2020 at 22:15
  • \$\begingroup\$ Every current through a wire causes heat. That aside, although the setup in the very-sketchy video draws “very little”, it’s not zero. That energy comes from somewhere. And that somewhere is the utility feed, which is metered. It’s not free-as-in-beer. \$\endgroup\$ Commented Apr 26, 2020 at 22:22
  • \$\begingroup\$ Just to be clear, tying neutral and ground together at the panel is standard practice, I assume your comment is directed to doing this at the socket? \$\endgroup\$
    – crasic
    Commented Apr 27, 2020 at 17:57
  • \$\begingroup\$ The key is that PE usually carries no current so the drop is reduced, if you swapped exactly half your loads in your house to using PE for return you would measure no difference at the receptacle \$\endgroup\$
    – crasic
    Commented Apr 27, 2020 at 17:59
  • \$\begingroup\$ Edited to clarify that the neutral-ground monkey business is at the plug, not the panel. Doing this might cause a GFCI to trip, if the branch is equipped with one. \$\endgroup\$ Commented Apr 27, 2020 at 18:08
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Of course not. The connection are called Live or phase, Neutral or return, and earth or ground. The neutral is connected to earth at some point in your home, so ideally neutral and earth should have no voltage difference. However depending on how the wires are routed, there will be return currents on the neutral wire. Since all wires have resistance, the current on neutral wire will cause voltage drop over it, so neutral will only have same potential as earth only at the place where they are connected.

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  • \$\begingroup\$ Neutral is connected to the ground/earth at some point 100 meters away from the house by the electrical company. The 'Ground' is a cable into the earth, common for the whole building \$\endgroup\$
    – Tasossssss
    Commented Apr 26, 2020 at 11:07
  • \$\begingroup\$ ... and that means that the neutral voltage will vary a lot with changes in neutral current. In a fault situation it could hit half-supply voltage. Forget your idea. \$\endgroup\$
    – Transistor
    Commented Apr 26, 2020 at 11:10
  • \$\begingroup\$ @Tasossssss your house would normally have a ground spike (or variation thereof) within a few meters of the main panel. It's not normal to only rely on the utility ground. \$\endgroup\$
    – brhans
    Commented Apr 26, 2020 at 15:18
  • \$\begingroup\$ In my house, neutral and earth are connected at the fuse panel in the cellar. Theorically one could use either wire for neutral or earth. But it's not always the case, and not always some 100m from the house, Sometimes the neutral goes back to the power plant. Or somewhere further up the distribution network. Connecting a load between neutral and earth can be very dangerous. \$\endgroup\$
    – Fredled
    Commented Apr 26, 2020 at 22:08
  • \$\begingroup\$ Sometimes there is even no neutral, but a combination of two 380V phases. If that would be the case he would have had a nice surprise by mesuring the voltage between the so-called neutral and earth. \$\endgroup\$
    – Fredled
    Commented Apr 26, 2020 at 22:09
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  1. It's not free.

  2. It's dangerous (that 2-3V could momentarily become hundreds of volts when an appliance is turned on or off).

  3. Unless you have faulty wiring you won't get much power out of it.

  4. This is not electrical engineering, it's a disgusting hack.

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    \$\begingroup\$ 5) Draw more than 20mA from neutral to earth and the RCD will disconnect power to your entire house. (GFCI for American readers) \$\endgroup\$
    – user16324
    Commented Apr 26, 2020 at 11:36
  • \$\begingroup\$ @BrianDrummond if it has one. \$\endgroup\$ Commented Apr 26, 2020 at 20:35
  • \$\begingroup\$ @BrianDrummond LOL. True. \$\endgroup\$
    – Fredled
    Commented Apr 26, 2020 at 22:30
  • \$\begingroup\$ @BrianDrummond unlike Europe USA generally does not have building RCD, opting for receptacle GFCI. I once knocked out power to my floor of hotel rooms during a stay in Europe by taking a faulty power strip that I had been using for years at home \$\endgroup\$
    – crasic
    Commented Apr 27, 2020 at 18:04
  • \$\begingroup\$ @crasic yes, arrangements vary, but OP said 220V, so I was only translating in case someone asked what an RCD was. In my house each RCD only darkens half the house. Good job on the hotel though! \$\endgroup\$
    – user16324
    Commented Apr 27, 2020 at 18:11
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What you're measuring is probably a combination of

  • neutral shift, due to the neutral conductor not being a perfect superconductor, but having a resistance and, unlike the protective earth conductor (what you called "ground"), carrying significant current
  • high-frequency crosstalk and radio pickup being misinterpreted by your multimeter as useful AC voltage
  • other measurement artifacts.

No, you cannot use it, and it's not free:

If it's actually a ground shift, it's already energy you pay for (and that voltage difference will instantly break down as soon as you stop having a load that leads to current in the neutral wire) and your devices suddenly using less payable energy at same power as soon as you add another current return path. Any energy that you have here HAS already passed your meter. And thus, you're paying for it – in this case, the energy is just used to ever so slightly warm up a neutral wire, but you're still paying for it. The energy doesn't come out of nowhere – it's actually missing from the useful power of your intentional loads.

If it's radio pickup: it's much more high-frequency than you think, and it will instantly break down as soon as you try to attach a load. Radio receivers deal with femto- to microamperes; that's the amount of current you could theoretically, after somehow magically converting that to DC, use. Even then, it's not free – the radio transmitter used electricity to induce it. Most of it is probably broadcast FM radio and TV; and in most countries it's forbidden by law to abuse broadcast radio to power anything but a receiver circuit.

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    \$\begingroup\$ Huh? Abuse broadcast radio to power anything? This wouldn't affect the transmitter in any way. Ḯ've never heard of such a law, and I see no reason why it would be necessary. \$\endgroup\$
    – vidarlo
    Commented Apr 26, 2020 at 19:59
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    \$\begingroup\$ I would still like to see example of such a law. Googling gave no hints... \$\endgroup\$
    – vidarlo
    Commented Apr 26, 2020 at 20:03
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    \$\begingroup\$ @MarcusMüller I have never heard of someone stealing a radio signal from their neighbour by building a bigger antenna. I'm not saying it's possible, but... \$\endgroup\$ Commented Apr 26, 2020 at 20:16
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    \$\begingroup\$ @MarcusMüller you'd have to build something like commons.wikimedia.org/wiki/File:Moosbrunn_SW_Antenna.jpg to even have a chance of creating an appreciable radio shadow for your neighbors, you still wouldn't absorb much power from it (mostly it would reflect), and if it's illegal it's because of zoning laws prohibiting 100m tall towers, not "abuse of radio". \$\endgroup\$
    – hobbs
    Commented Apr 26, 2020 at 20:17
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    \$\begingroup\$ @MarcusMüller I doubt that an "elektrischen Anlage", as reasonably defined, exists here... but also you would have to actually succeed in harming your neighbor, thanks to 248a. \$\endgroup\$
    – hobbs
    Commented Apr 26, 2020 at 21:54

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