How High Does Voltage Have To Be Before It’s a Serious Hazard?

Voltage in itself isn’t dangerous. A 10,000–volt shock can be no more disturbing than a pinprick, but you can get a serious jolt from a 12–volt automobile battery. What’s dangerous is the amount of electric current that flows through your body as a result of the voltage.

A current of electricity, as you undoubtedly know, is a flow of electrons. The voltage is the amount of push that urges them to flow from one place to another. If they are given no place to flow to, no amount of urging by a voltage will make them flow. Voltage is like height: No matter how high you may be on a cliff, the height is harmless as long as you don’t take a direct route to the ground below. Electrical safety is simply a matter of making sure that the electrons can get to the ground by a route other than through your body; they can’t hurt you if they’re not flowing through you. That’s why the birds are safe perching on high-voltage transmission lines.

But it’s high time we focused on those electrons that I talk about in several places throughout this book.

Electrons are the negatively charged particles that make up the entire bulk of all atoms. Every atom of every substance is essentially a blob of electrons with an incredibly tiny, incredibly heavy, positively charged nucleus buried somewhere in the middle.

The electrons in atoms have certain energies that are characteristic of the type of atom they’re in. What makes a flow of electricity possible is that many of these electrons are easily detachable from the rest of their atoms and will travel elsewhere under the influence of a voltage shove. In most cases it takes only a few volts to evict at least some of them from their home atoms.

Some electrons are so loose that you can just rub them off. Scuff your shoes across a carpet on a dry day and some electrons will be rubbed off your shoes’ atoms onto the carpet. Because your feet are presumably firmly connected to your shoes, your entire body now has a deficit of electrons, while the carpet has a surplus. Normally, all atoms are electrically neutral, because they have just as much positive charge in their nuclei as they have negative charge in their electrons. But now, your body has fewer electrons than your atoms require.

If you now touch an electron conductor such as a metal radiator or water pipe, electrons from the huge supply in the rest of the world, the ground,  will eagerly leap to your finger even before it touches the metal, lighting up the intervening air with a crackling blue spark and inspiring you to utter an expletive. Instead of a water pipe you may even touch another person, who is unlikely to be as electron-deficient as you are, and some of his electrons will jump to your finger, eliciting an expletive from him.

But here’s the thing: The voltage that urged the electrons to flow into your finger from the water pipe or your shocked friend may have been several thousand volts, but you’re not dead because the number of flowing electrons, the amount of current, was much too small to do any harm to your body. After all, your shoe soles aren’t exactly electric generators, like the ones down at the power plant that push gazillions of electrons through transmission lines to your house.

At home, where the voltage has been reduced to 120 or 240 volts, if you touch a “live” wire while some other part of you is connected to the ground, the power company will blindly supply as many electrons as can possibly flow through your body, that is, as large a current as can flow through you, given your body’s resistance to the flow. And you’re a dead duck.

In short, the danger of electricity lies not in how many volts you are subjected to, but in how much electric current flows through your body. The trouble is that we never know what the current can or will be in any given situation, so we must stay away from any voltage above battery levels at all times.