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We all know that birds don't get electrocuted while standing on a single power line, but if the bird touched the ground while holding the power line, it will die instantly.

One thing that riddles me is that I don't understand why the bird doesn't act as "ground" while touching the power line with voltage of 120v while the bird has a voltage of 0v. the potential between the two is 120v. why is it that only when the bird touches the ground that also have voltage of 0v the bird dies?

Adam77
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1 Answers1

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The bird doesn't have a voltage of 0V, its voltage is floating, which means that it has the same voltage as anything it touches.

As soon as the bird touches ground, the bird gets a voltage of 0V. When it takes off, it is floating again. When it touches the powerline, it gets a voltage of 120V.

Only when it touches the powerline and the ground at the same time, one end of the bird has 120V, and the other end of the bird has 0V, which means that a current will flow, killing the bird.

Also, what makes ground ground is convention, nothing more. If the powerline was DC (unlikely I know, but for simplicity, bear with me), we could declare that the ground has a voltage of 1,000,000V, and the powerline has 1,000,120V. Or that the ground has -120V and the powerline has 0V. But neither of those would be very practical in daily use.

Dampmaskin
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    In this case 'what makes ground ground' is not convention but actually connecting the neutral of the transformer to a real earth ground. – vu2nan Apr 08 '20 at 11:34
  • Yes, both equating and basing the electrical ground of the real earth ground are conventions and practices that make all sorts of sense. :) – Dampmaskin Apr 08 '20 at 12:04