Question on Mains return current

Since the neutral wire is grounded at the circuit breaker panel, I am confused as to whether current actually flows along the neutral back to the service head?

If not, then what actually absorbs the current? (I realize that it is AC, but the current must be going somewhere during a single cycle).

• I think this wiring arrangement depends on where in the world you are. Where I'm originally from (South Africa) neutral is not grounded at your panel, but is grounded back at the utility service transformer 'somewhere down the road'. Feb 23, 2015 at 14:51

Perhaps the below sketch will help. This is earthed according to Australian practice (AS 3000).

Note that the dirt ('general mass of the earth') is high impedance and no appreciable current flows between the earth electrodes. Therefore, any current flowing via the active conductor must return via the neutral conductor, since there is no other possible path for it to flow.

Q: "If there is no appreciable current between the earth electrodes, then why is it dangerous to touch a live wire?"

A: Touching a live wire does not, itself, kill you. Note that birds are quite happy to sit on powerlines.

What kills you is completing a circuit between active and earth (or neutral). A very direct way of doing this is shown below. Note that many things are bonded to earth - the steel frame of your house, the reinforcement bars in concrete slabs, plumbing (metallic water services must be bonded to earth in Australia), and so on.

You don't even have to touch two metallic conductors to be electrocuted. Ground has 'high' resistance but not infinite resistance. Therefore, when a live wire touches the ground, a current diffuses into the ground, eventually returning to the source. If you present a lower resistance path for this current, it will flow through you. This is the concept of 'touch voltage' and 'step voltage' which we must consider when designing high-voltage installations.

Touch voltage is very bad, because if you touch a live conductor with your hands, and the current flows to your feet, it will traverse across your chest i.e. your heart. The heart is very sensitive to electric shock.

Step voltage is not so bad, because the current flows into one leg and out the other. There are no really important organs between your legs.

As an aside - we have had incidents where crane drivers have contacted HV overhead lines. The recommended action is to stay in the crane as the surrounding metal is all at the same voltage, so you won't be electrocuted. If you do have to run away, i.e. because the crane is on fire, the recommended action is to jump off (so you don't touch the metal of the crane, and the ground at the same time - they may be at different voltages) and then bunny hop away with your feet close together. Keeping your feet close together minimises the voltage between your feet.

Yes, I am serious.

• If there is no appreciable current between the earth electrodes, then why is it dangerous to touch a live wire? Feb 25, 2015 at 16:42
• @Darren: See edit above. Feb 27, 2015 at 12:50
• Nice answer. Why do you have to bunny hop away? If you run, only one foot touches the ground at a time. Feb 27, 2015 at 13:01
• Kynit: before you are running, you have to make a running start, which probably involves two feet on the ground. I'd rather hop. Feb 27, 2015 at 13:09
• I really appreciate your detailed answer. Thanks! However I'm not sure I agree with the statement "There are no really important organs between your legs" :) Feb 27, 2015 at 15:48

It goes back to the transformer on the pole. Grounding is just for safety. The pole transformer should also be grounded and there should also be a neutral wire between the service panel and transformer where the return current will normally flow.

• Please kindly add a rough schematic if possible.. Feb 22, 2015 at 19:31
• If both the breaker panel and the pole are at zero volts, then why would there be current flow between them? Feb 22, 2015 at 19:55
• If you draw 10A on the hot, then 10A will flow in the neutral wire both to your service panel and at the transformer. This current flow will produce a voltage drop in the neutral wire between the service panel and the transformer. The ground rod does provide another current path to the ground rod connected to the transformer, but this will be a much higher impedance path. Feb 22, 2015 at 20:34
• I guess this is where I am getting confused. If the neutral wire is grounded at both ends, then how can there be a voltage drop? Feb 22, 2015 at 21:51
• 'grounded' just means connected to a ground rod. Dirt is not a superconductor, hence if current flows you will get a voltage drop. Feb 22, 2015 at 21:53