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Of course we are not talking about code or best practice, but hypothetically if someone wanted to do some welding a few hundred meter from the closed power point could he/she run one hot conductor to the site and just bury the neutral in the ground and get to welding?

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  • \$\begingroup\$ A similar question came up some time ago. It turns out that there are some places in some countries where the earth has been used as a conductor. But I believe this was done with much higher voltages and lower currents and longer distances. I doubt you will get good enough conductivity for a low voltage welder. (Low voltage meaning less than 500 V). \$\endgroup\$
    – user57037
    Commented Mar 15, 2021 at 7:27
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    \$\begingroup\$ en.wikipedia.org/wiki/Single-wire_earth_return \$\endgroup\$
    – user57037
    Commented Mar 15, 2021 at 7:29

4 Answers 4

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Aside from (obvious?) danger, the typical ground resistance is too high for that to work.

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Chris's question is not 100% clear. Leaving aside safety and the rest, and focusing on feasibility, it may be interpreted as if you have a conductor in the soil or the soil alone.

  1. conductor in the soil, as a grounding system nearby: provided cross sections are sufficient (e.g. refer to BS7671 or IEC 60364-4-41 for the cross sections that should be used if you ground your "equipment", or make a full calculation with BS7430 or IEC 60364-5-54). Of course, if there are other users of the same grounding system, the might be affected by the sudden current spikes flowing in it.
  2. using soil alone, as @mkeith said, it depends on the soil resistivity. When you perform soil resistivity measurements, your instrument tells you first the resistance between the voltmetric electrodes and then calculate the soil resistivity: the former values are not so large, in the order of some ohm for most soils.
  • Example: a soil resistivity of 33 ohmm, gives you 0.5 ohm for a measurement at 12 m separation. The wider the separation the larger also the depth of the ideal half sphere between the two electrodes and thus the used volume of soil. If you are some hundreds m apart you have a some hundreds m long some hundreds m deep half sphere; in common soil with less than 100 ohmm resistivity it gives you let's say 1 ohm.
  • Two ingredients: Now, what you need is i) good coupling with the soil, and ii) the possibility of putting so much current in the soil from your Low Voltage distribution (protection relay!). i) good coupling = you must bury a copper conductor of several meters, or better a metallic plate or large tape (see IEEE Std. 80 or BS7430 for its resistance). ii) your welding machine must be insulated by a transformer otherwise zero sequence relay will trip, or remove the relay.

Now: isn't it easier/safer to bring a long three-conductor cable sized for the voltage drop, such as a 3x4 mm2 and put your welding machine there near the point where you want to work? A bit more expensive in terms of Cu$ (copper money), but easier and linear to implement.

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No

Again No

Not safe, not advised to even dream about it.

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  • \$\begingroup\$ I was scandalized, but it is happing right now.... i just want to understand the physics of how it is working . \$\endgroup\$ Commented Mar 15, 2021 at 23:44
  • \$\begingroup\$ @chrisalyui the physics is really not complicated. Current is flowing through the ground instead of a wire. \$\endgroup\$
    – user57037
    Commented Mar 17, 2021 at 6:30
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Hypothetically, ignoring all safety and such, it could work if and only if the resistance of the ground leg is small enough to conduct enough current for the welder to do its job. I know that very dry soil, and hard frozen soil and bedrock do not conduct electricity very well. So the best chance for success would probably be in a place where there is lots of damp soil.

I have never measured soil conductivity quantitatively and I am not sufficiently motivated to research the topic. But I know from experience and lore that electric fences become ineffective in very dry climates and hard frozen climates due to the lack of conductivity in the soil.

I also know from a previous question and answer that in some cases, power is actually distributed from utility companies via a single wire, relying on earth to return the current to the source. Here is the wikipedia:

https://en.wikipedia.org/wiki/Single-wire_earth_return

Note that in the case of utility installed systems there is an isolation transformer involved and customer premise wiring does NOT use soil or earth as a current carrying conductor.

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