Electronic – Free-as-in-beer power from neutral and ground


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

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


  • 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?

Best Answer

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’.