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Avoiding Shocks Like the Plague

Your body is a delicate machine. Electric shocks, depending on certain conditions, can be fatal, even at relatively low voltages. What comes out of your wall outlet is deadly if you play around with it. Even electrical gadgets working off batteries can cause you serious damage.

How voltage and current can get you

Your body is like a big resistor. Usually, your body’s resistance is high enough to prevent damage when you’re exposed to low voltages. However, certain conditions can lower your body’s resistance, lowering the amount of voltage needed to cause you serious damage, such as giving you a nasty burn. Those conditions might include handling electronics with sweaty palms or trying to change your 12 volt (V) car battery on a rainy day — either can turn a slight tingle into a fatal event.

Both AC (alternating current, such as the power from your wall outlet) and  DC (direct current, such as from a battery) voltage can damage you in different ways:

AC voltage: This type of voltage regularly reverses direction. This can cause your heart to shift its regular beating pattern in a condition known as ventricular fibrillation. If this happens, your heart muscles go out of whack in a way that causes blood to stop pumping. In this situation, even if you cut the current, your heart might not be able to find its proper rhythm, and you could die.

DC voltage: This type of voltage is on constantly and causes your muscles to contract and seize up quickly (including your heart muscle). If you grab an electrical device in conditions that cause your body to conduct DC voltage, your hands could become frozen (unable to let go of the device), and your heart could stop. If someone cuts the current quickly, though, your heart might begin to beat again (and you’ll be able to attend that Rotary luncheon next week).Short of killing you, electric shock can cause burns as the current dissipates across your body’s natural resistance (that is, your skin).

How much is too much?

Most resistance in your body is in your skin. If your skin is wet or damp, that resistance is lowered. If you handle an electrical device with damp hands, even voltages under 20V or so (not enough to even light a low-wattage lamp) might be sufficient to do you serious damage. The 120V coming out of your electrical outlet has a lot of punch: more than enough to kill you.

Four AA batteries in series — which is what we use in the projects in this book — generate only about 6V. We did that on purpose to keep you relatively safe. Just because AA batteries don’t have a high voltage output, don’t think that they can’t hurt you. If you short them out, all the electrons will flow quickly from the negative to the positive poles and generate a lot of heat — enough heat, in some cases, to destroy the battery and possibly burn you. If you feel heat coming from your circuit or the batteries, you might have a short-circuit or a component inserted the wrong way. Turn it off and let things cool down; then check to see what’s causing the problem.

The resistance in your body can vary greatly. For example, if you have sweaty hands and touch a live wire with one hand while the other hand rests on a metal table, this is a very dangerous situation. Because you have moisture on your hands — which lowers your contact resistance — a higher current will flow through your body for a given voltage. If you have dry hands — one hand touching a live wire, the other hand in your pocket — and your feet on a dry, rubber mat, there’s far less danger from the same amount of voltage because your resistance is higher. However, if a higher voltage comes your way, even with the higher resistance, you could die. Bottom line: There is no iron clad rule as to what level of voltage will kill or seriously injure a person because of all the variables. Regardless of how much voltage you work with, develop safe work habits now.

Is it the voltage or the current — or both?

Electricity is the movement of electrons (current) through a conductor when a voltage is applied across the conductor. Electric current is what burns your skin, stops your muscles cold, and causes your heart to go into fibrillation. If you touch a live wire (that is, any conductor at some voltage), current can flow through your body because it is a conductor. The amount of current that flows through your body depends upon your body’s resistance to the flow of electric current and how much voltage is applied.

Ohm’s Law deals with the relationship between voltage, current, and resistance. Here’s the law, for those among you who appreciate equations:

Current = Voltage ÷ Resistance

The calculation for what’s dangerous involves the current, the voltage, and your body’s resistance. The current passing through your body is equal to the difference in the voltage that’s being applied to two spots on your body (for example, your hand touching an electric circuit and your feet touching the floor, or one hand touching a live conductor and another hand resting on a chair), divided by your body’s resistance.

Common sense: Protecting yourself from getting shocked

Although you should always use care working with electricity, we want to let you know some common situations to avoid that could turn your body into a super conductor. You know you shouldn’t stick your finger into an electrical outlet (we hope!), but you should also get into some other good habits. Read on.

Rings are out

Metal is a dandy conductor. Wearing rings or other metal jewelry around electricity is a lousy idea. For example, when the skin on your finger is surrounded by a ring (a terrific contact point) and you touch a voltage source, your body’s resistance can be very low. In that state, even a lower voltage jolt could do you serious damage. Leave jewelry somewhere else. (Tell your spouse or fiancée that we said it’s okay for you to take off your wedding ring when working with electricity.)

Another good reason to avoid jewelry is that it can snag on things. Imagine working on a breadboard filled with wires and tiny components, only to have your ring or necklace catch on something and yank it out. At the least, you have to put the component back in place; at the worst, you could damage the component and have to replace it.

Beware of water!

Don’t work in a wet environment (say, outdoors on a rainy day, or while standing on a damp garage floor). This prevention might seem obvious, but consider that cup of coffee on your workbench. What would happen if you knocked it over while working with electricity? You need to become super careful about anything wet or moist in or near your work area. This includes you: If you just came in out of the rain or from a run, dry off before working on electrical equipment.

Respect electricity

Here’s one simple rule that you should memorize right now: Never touch a component in a circuit that has power (an energized circuit). Turn off all power sources or remove the source from the circuit entirely before touching it. One trick that electricians use is to keep their left hands in their pockets when working with electrical equipment. If a zap occurs, it will flow from their right hands to the ground — not from hand to hand, passing right through the heart.

You shouldn’t be working with live electricity — ever! — but this trick of trade used by more advanced users shows how important it is to understand how electricity works and respect its authority.


Even when the source is removed, some electricity might remain. To be absolutely sure, before you touch anything, test the circuit with your multimeter. (We talk about how to use a multimeter in "Discovering schematics".) And don’t take somebody else’s word that the power is off; always check and double-check this yourself!

Don’t work with AC-operated circuits unless you absolutely have to. And if you do, it might not be a bad idea to have a friend nearby who is trained in CPR. Visit www.redcross.org for more information about CPR training.