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In 3 phase transmission lines we have different voltages depending on how we measure it. Phase to phase voltage is going to be 1.73 times more than phase to neutral. So far I understand everything that I've just said. Now, phase to neutral has the same voltage as phase to earth. This means that phase has a higher potential than earth and that earth has a lower potential than phase which would in theory be 0 V. Why is earth at 0 V with respect to phase and not floating?

The only reason I think that earth is at 0 V (with respect to phase) is because at the power station there is a metal pole stuck to the earth which is connected to neutral thus allowing current to flow through the earth and up the neutral pole. If there weren't a pole, current wouldn't flow through earth and earth would not be at 0 V it simply would be floating. Right?

Any help is greatly appreciated.

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    \$\begingroup\$ Why is the number 0 the value 0 with respect to 0? \$\endgroup\$ – Harry Svensson Nov 4 '18 at 10:08
  • \$\begingroup\$ Yes, you are right. It is the use of frequent points of tethering to local Earth that ties the system down close to Earth. The use of copper stakes, Ufer grounds, etc. Otherwise systems and remote sections would indeed float. Floating has value. Grounding has value. There are times to prefer one or another. But for households, it is considered safer, after much gnashing of teeth, to not float but instead to keep the system tied close to local Earth. \$\endgroup\$ – jonk Nov 4 '18 at 10:38
  • \$\begingroup\$ There are problems this creates. If you live near a smelter, for example, which uses huge circulating currents, the currents in the Earth itself will create large voltage differences which can literally force copper and silver to migrate and plate off, requiring periodic replacement of copper busbars, for example. Every approach has benefits and costs. It's all a two-edged sword. You make choices and then live with them. \$\endgroup\$ – jonk Nov 4 '18 at 10:42
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Yes, in some grounding schemes (eg. TN) N is grounded at the power station end and that is what makes N = E. In some other systems like IT, N is not grounded and the Ls are floating.

Look up grounding schemes/grounding systems.

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