Electrical – Shock from Capacitive Coupling


In an AC supply which is not earth grounded, I see a small amount of current flowing to ground from both wires of the supply (live wire has higher) even though the circuit is incomplete.

It is due to capacitive coupling? Can anyone explain it?

And why do I get more current from the live wire to ground than the neutral to ground even though neither are grounded?

Here is a photo for context.

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Best Answer

I see where the diagram is attempting an isolated system. However, that is wrong. The system is not isolated: it is bonded to earth. You can't miss the neutral-ground bond in the diagram; it looks like a human!

What can be said about isolated systems is "the first ground fault is free". It doesn't do any harm, because the systems aren't connected except for that, and that does not complete a circuit. This first ground fault effectively becomes the neutral-ground bond. That can work in an industrial setting where there is staff maintenance doing frequent testing to detect that "first ground fault" and fix it before there is a second.

In your ideal diagram, the human is not shocked because he's the only ground fault. However if there's a second ground fault, he's dead.

Capacitive coupling doesn't tingle. What's more, capacitive coupling can't occur at all unless wires are running in parallel for some distance. You are trying to use "capacitive coupling" as a catch-all for all unexplained current and that's just wrong.

We often get people on diy.se who say they've replaced their GFCI 3 times and can't understand why it trips when they use their expresso machine. Duh, but they are too vain to accept their precious little appliance could possibly have a ground fault. Don't fall into that trap.

Newsflash: Your machine isn't isolated. If it's supposed to be isolated, then it has a ground fault. That's why it shocks you when you touch it.

The reason more current flows hot-earth than "neutral"-earth is that the ground fault is closer to "neutral" than to hot.