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Pre-face: My step-father and I were turning the heat down on the water heater. He demonstrated that touching the ground wire doesn't shock you.

My understanding is that the ground wire doesn't have current unless the case of a short-circuit, or over-abundance of energy. The wire also has very little resistance.

My question, if the water heater had a short-circuit or had an access flow of energy. Would he have been shocked? Please explain instead of yes or no.

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No.

The elementary idea of grounding is that excess current finds an easier way to the ground than through your body.

If you're wet, you 'may' in minimal probability get a minor shock, but unless your body offers the current a path easier or at least comparable to the metallic ground wire, the answer is no.

EDIT: Current gets divided in inverse ratio to resistance offered by the paths, hence very less or in this case negligible current flows through a path which has a very high resistance compared to the other.

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  • $\begingroup$ Current goes through all paths available to it regardless of resistance. The idea of least resistant path for current has been proven false. $\endgroup$ – Mason T. Mar 24 '14 at 16:11
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    $\begingroup$ @NappaTheSaiyan It gets divided in the inverse ratio of resistance. So, if one of the path has 1000 times the resistance as the other, it'll have 1000 times less current as the other. Practically, negligible. That's what I mean. As far as I know, it was never a myth. Was it? I would like to see some reference. $\endgroup$ – Cheeku Mar 24 '14 at 16:13
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    $\begingroup$ I understand what you're saying since, the wire has such low resistance almost all the current will flow through it. So only a small amount will flow through the higher resistance which is your body. $\endgroup$ – Mason T. Mar 24 '14 at 16:16
  • $\begingroup$ The amount of current flowing in the ground doesn't matter as long as the ground is a good one. The voltage on the ground wire is zero regardless of current, excepting highly unusual extreme cases. But you still might get a shock for reasons unrelated to the current if your other hand is touching something "hot", or if you've developed a static charge (e.g. rubbing your shoes on a carpet). I don't think those situations are what the OP had in mind, though. $\endgroup$ – garyp Mar 24 '14 at 16:41
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The answer is "no". Assume that the ground wire has a resistance of 1 ohm, and your step father has a resistance of 100,000 ohms, which is actually a bit lower than the "normal" value when measured with dry hands. This means that your step father will experience a current flow that is 1/100,000 times the current flow through the ground wire, assuming that there is a short circuit in the water heater. In addition, since the ground wire has such a low resistance, there will be a LARGE current flow through it. This current flow will immediately trip the associated circuit breaker, shutting off current to the water heater. Unless your step father happens to be touching the ground wire at EXACTLY the time that the short circuit happens, there will be no current flowing through him. Even if he is unlucky enough to touch the ground wire at the exact wrong time, the current flow through him will be so low, and last for such a short duration, that no harm will occur.

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