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suppose I am using very good earths ( let 2 numbers) at my home to avoid the risk of failure of neutral of electric company. Then should I common my earth with neutral? But if this is done the in case of failure of neutral, other consumers may load my earth, leading to over heating. So can I rely completely on my good quality earths and break the neutral of electricity company?

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    \$\begingroup\$ Safety is a very complex question in the environment you are hinting towards. Besides, even in the best of cases there are reasons to tie neutral to ground and reasons not to do so. It depends on context. And that's when you know the situation reasonably well. So I can't imagine that anyone can offer a good answer given how little you know (or perhaps even could know) about your circumstances and what you are doing yourself, or your neighbors are doing, or what kinds of failures are common with your supplier company. You need local, trained advice. \$\endgroup\$ – jonk Nov 13 '17 at 7:57
  • \$\begingroup\$ you cannot use earth as return for your house power because you will induce current in the soil that can be felt by someone walking barefoot on the ground. depending on circumstance, it could even cause injury. \$\endgroup\$ – jsotola Nov 13 '17 at 8:05
  • \$\begingroup\$ @jsotola guess what ground is in almost any power system? Exactly, a well-grounded earth prod of some kind. So, while you're technically right, for very high currents and very bad earth connectivity, a voltage gradient might be measurable at floor level, I don't think this is a valid concern here. \$\endgroup\$ – Marcus Müller Nov 13 '17 at 8:09
  • \$\begingroup\$ @jsotola See en.wikipedia.org/wiki/Single-wire_earth_return \$\endgroup\$ – pipe Nov 13 '17 at 8:24
  • \$\begingroup\$ Technically you could have your own delta-Y transformer and have your own local ground for your own local neutral. Legally, you have few to none options depending on where you live. \$\endgroup\$ – winny Nov 13 '17 at 8:27
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How you should connect your earth and neutral will be dictated by your local wiring codes. Your supplier may be unhappy if you don't follow them. The same goes for anybody you manage to electrocute.

That said, unless you have gone to a lot of trouble to achieve a very low earth impedance, the chances are that the worry about other people's supplies through your earth is less of a problem than you think it is.

A simple earth rod may only achieve impedances in the tens to hundreds of ohms. If that's the case, then even a dead short between supply and earth will only allow a few ones or tens of amps to flow. Using appropriate gauge wire between your main earth terminal and the earth rod will keep that safe. This limit will apply no matter how many other consumers' supplies are attempting to use your earth connection.

Singe wire earth return supplies - ones with no neutral connection - only really work at high voltages. At normal domestic voltages, the voltage lost at the earth rods soon becomes excessive. You don't say what your supply is, so let's assume 30A at 230V. Let's assume that you have somehow managed to get down to 1 ohm on your earth connection (perhaps the foundations of your building are reinforced conductive concrete), and the suppliers have done the same at their transformer. That's 2 ohms total. If you now try to pass 30 amps through this, you'll drop 60 volts just in the earth connections, and your supply will be down to 170 volts.

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  • \$\begingroup\$ "... the worry about other people's supplies through your earth ...". It's real enough. I know of one case where a chap rewired his terraced house. On passing by the fuseboard he noticed a smell of melting plastic. It was from the earth wire which, in Ireland, is connected to neutral at the incoming supply. The older houses didn't have a neutral link so when the utility neutral broke his house was the return path via ground for the whole terrace. \$\endgroup\$ – Transistor Nov 13 '17 at 13:00
  • \$\begingroup\$ @Transistor That tends to happen if there's a shared metal utility pipe (water or gas). In such cases, the bonding wire from the utility to the main earth terminal, and from the main earth terminal to the supply cable, needs to be quite substantial. \$\endgroup\$ – Simon B Nov 13 '17 at 16:13

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