IN THIS CHAPTER

check Knowing the risks of working with electricity

check Protecting yourself from the perils of stray electricity

check Safeguarding your gear from static electricity

When I was a kid, I helped a good friend named Barry who built a Tesla coil. By “helped,” I mean that I hung out in his garage and watched while he meticulously wrapped thousands of turns of bare copper wire around a huge glass milk bottle, painted it with dozens of coats of lacquer, and polished the brass ball that attached to the very top of the coil. I’m quite certain he couldn’t have done it without me.

When it was done, we plugged it in and marveled at what it could do. Sparks flew at random a foot or two into the air from the ball at the top of the coil. If you held a crowbar in one hand, you could draw a spark several feet from the ball to the crowbar. The current coming off the ball flew through the air and into the crowbar, and then passed through our bodies and into the ground. You could also light up a fluorescent light tube simply by holding the tube in your hand within a few feet of the coil.

To this day, I cannot believe Barry’s parents let him build it. I know my parents wouldn’t have let me build one. My mom was kind of like the mom in A Christmas Story, who wouldn’t let her son Ralphie have a Red Ryder BB gun (the one with a compass in the stock and this thing that tells time) because “you’ll shoot your eye out.”

That was my mom. No Tesla coils for me. Too dangerous.

None of the electronic projects described in this book are anywhere near as dangerous as a Tesla coil. In fact, most of them pose no threat at all. That being said, it’s important to remember that whenever you’re working with electricity, you’re working with something that’s potentially very dangerous.

The possibility of electric shock is always present whenever you work with electricity, but there are other potential dangers as well. You probably won’t shoot your eye out, but if you’re not careful, you might start a fire or otherwise injure yourself or someone else.

The purpose of this chapter, then, is to keep you safe while you experiment with electronics. Please read it well, and please heed every bit of advice I give here.

Facing the Realities of Electrical Dangers

There’s no escaping the simple fact that an electric shock, if strong enough, can kill you. So whenever you work with electricity, you must be sure to take every precaution you can to avoid being the recipient of a shock strong enough to do damage.

In the United States, somewhere between 500 and 1,000 people die every year from accidental electrocutions. Many of those are industrial or weather-related accidents in which people come into contact with downed power lines. But many of them are completely avoidable accidents that happen in the home. In the sections that follow, I give you specific guidelines for avoiding accidental electrocution.

Household electrical current can kill you!

Too many people are under the false impression that the 120 volts of alternating current running through household electrical wires isn’t enough to kill. So let’s start by getting one fact straight:

The electricity in your home wiring system is more than strong enough to kill you.

You’re exposed to household electrical current primarily in two places: in electrical outlets and in the lamp sockets within light fixtures. As a result, you should be extra careful whenever you plug or unplug something into or from an electrical outlet, and you should be careful whenever you change a light bulb. Specifically, you should follow these precautions:

Never change a light bulb when the light is turned on. If the light is controlled by a switch, turn the switch off. If the light isn’t controlled by a switch, unplug the light from the wall outlet.
If an extension cord becomes frayed or damaged in any way, discard it. When the insulation begins to rub off of an extension cord, the shock hazard is very real.
Never perform electrical wiring work while the circuit is energized. If you insist on changing your own light switches or electrical outlets, always turn off the power to the circuit by turning off the circuit breaker that controls the circuit before you begin. Many people die every year because they think they can be careful enough to safely work with live power.
Never work on an AC-powered appliance when it has power applied. Simply turning the appliance off isn’t enough to be safe. If the appliance has a power cord, unplug it before you work on it. If it doesn’t have a power cord, turn off the power to the appliance by throwing the circuit breaker on your home’s electrical panel.
Take extra precautions when you’re working with your own AC circuits. In Book 4 , I tell you more about working with AC circuits; I say more about AC safety then.

IS IT TRUE THAT CURRENT, NOT VOLTAGE, KILLS?

There is an old adage that “it’s the current that kills, not the voltage.” Although this statement may be technically true, it’s also dangerously misleading. In fact, it stems from a fundamental misunderstanding of what current and voltage are. It can cause you to take dangerous risks if you don’t understand the relationship between current and voltage.

The danger from electric shock occurs as current passes through vital parts of your body — specifically, your heart. It takes only a few milliamperes of current to stop your heart. At somewhere around 10 mA, muscles seize up, making it impossible to let go if you’re holding a live wire. At around 15 mA, the muscles in your chest can seize up, making it impossible to breath. And at around 60 mA, your heart can stop. It takes only a few moments of exposure for these effects to occur.

So yes, it is current passing through your body that can kill you.

But current is inseparable from voltage. Current can’t happen without voltage, and all other things being equal, the greater the voltage, the greater the current. As a result, it’s very difficult to receive a lethal shock from three volts even if you’re dripping wet and standing on bare concrete. But under those conditions, 30 volts may be enough to create a painful and damaging shock.

Saying “it’s the current that kills, not the voltage” is kind of like saying “it’s lack of oxygen, not water” that causes drowning. Although it may be technically true, isn’t it the water that causes the lack of oxygen?

Even relatively small voltages can hurt you

Most of the projects in this book work with AA batteries, usually two or four of them tied together to produce a total of three or six volts. That’s not enough voltage to do serious harm. Even if you do get a shock with three or six volts, you will probably barely feel it.

However, it’s possible to injure yourself with voltages even as low as three or six volts. If you accidentally create a short circuit between the two poles of a battery, a lot of current will flow very fast. This will very likely cause the wire connecting the two ends of the battery to get very hot, and the battery itself may also heat up. The heat may be enough to inflict a nasty burn.

If the racing current goes unchecked, there’s also the possibility that the battery will explode. Trust me; you don’t want to be nearby if that happens. You really don’t want to make a trip to the emergency room to have fragments of an exploded battery removed from your eyes.

As a result of this danger, you should take the following precautions when working with the battery-powered circuits described in this book:

Don’t connect power to the circuit until the circuit is completely finished and you’ve reviewed your work to ensure that everything is connected properly.
Don’t leave your circuits unattended when they’re connected to power. Always remove the batteries before you walk away from your workbench.
Periodically touch the batteries with your finger to make sure they aren’t hot. If they’re getting warm, remove the batteries and recheck your circuit to make sure you haven’t made a wiring mistake.
If you smell anything burning, remove the batteries and recheck your circuit.
Always wear protective eyewear to protect yourself against exploding batteries. (Under the right circumstances, other components can explode as well!)

STAYING SAFE BY STAYING DRY

We’ve all seen murders committed on TV crime dramas by throwing a plugged-in electrical appliance such as a hair dryer into a bathtub while the victim was taking a bath. I’ve always wondered how often that really happens, and how likely it’s fatal. For example, how quickly would the circuit breaker kick in and cut power to the hair dryer? Would the special GFCI-protection devices required in all bathrooms work as designed and cut power to the hair dryer in time?

I’ve never wanted to conduct an experiment to actually find out — nor should you, under any circumstances. Water and electricity are a very bad combination because water is an excellent conductor of electricity, and it flows everywhere.

Strictly speaking, pure uncontaminated water is actually an insulator. But pure water is very rare. Most water is filled with contaminates, and those contaminates turn the water into an excellent conductor. Thus, it’s true that you should avoid water when working with electrical current. Here are a few tips for staying safe by staying dry:

Make sure the floor is dry. Don’t work on electronic or electrical devices in an area where the floor is wet.
Beware of high humidity, especially if it condenses into moisture on your projects.
Dry your hands before working with electrical current. Even a small amount of sweat on your hands can lower your body’s natural resistance and accentuate the danger of electrical shocks from lower voltages.

Sometimes voltage hides in unexpected places

One of the biggest shock risks in electronics comes from voltages that you didn’t expect to be present. It’s easy enough to keep your eye on the voltages that you know about, such as in your power supply or batteries, but some electronic circuits are designed to amplify voltages. So even though your circuit runs on 6-volt batteries, there may be much larger voltages at specific points within your circuit.

In addition, some electrical devices can actually store electric charge long after the power from your circuit has been disconnected. The most notorious device with this characteristic is the capacitor, which alternately builds up and then releases electrical charges. Thus, you should be wary of any circuit that contains capacitors — especially if the capacitors are large. Common ceramic-disk capacitors, which are typically smaller than a tiddlywink, don’t store much charge. However, if your circuit has capacitors the size of batteries, you should be very careful when working around them. Such capacitors can hold large charges long after the power has been cut off.

Here are some safety points concerning capacitors:

One of the most common places to find large capacitors is in the power-supply circuit. Any electronic device that plugs into a household electrical outlet has a power-supply circuit that may contain a large capacitor. Be very careful around these capacitors. In fact, if the power-supply circuit is inside its own enclosed box, don’t open the box . Instead, replace the entire power supply if you suspect it’s bad.
Another common place to find high-voltage capacitors is in a flash camera. Even though the battery may be just 1.5 V, the capacitor that drives the flash unit may well be holding a charge of 300 V or more.
Before working on a circuit that contains a capacitor, always discharge the capacitor first. You can discharge small capacitors by shorting out their leads with the blade of a screwdriver. Make sure you touch only the insulated handle of the screwdriver while you short out the leads, and don’t touch any other part of the circuit with your free hand.
Larger capacitors should be discharged by connecting their leads to a lamp or a large resistor. The easiest way to do this is to wire up a lamp holder to a pair of alligator clips, screw a lamp into the lamp holder, then carefully connect the clips to the capacitor leads. If the capacitor is holding a charge, the lamp will glow for a moment as the capacitor discharges through the lamp.
If you don’t feel completely confident in what you’re doing where large capacitors are concerned, walk away from the project.

Other Ways to Stay Safe

Electric shock isn’t the only danger you’ll encounter when you work with electronics. The following paragraphs summarize a few of the other risks you may be exposed to and describes the precautions you should take to minimize those risks:

Soldering poses an obvious fire hazard. If your soldering iron is hot enough to melt solder, it’s also hot enough to ignite combustible materials such as paper, wire insulation, and so on. Therefore:
- Always be aware of when your soldering iron is on. Don’t plug it in until you need it, and unplug it when you’re finished soldering.
- Never set a hot soldering iron down directly on your workbench. Instead, get a soldering iron holder to safely hold the soldering iron while it’s hot. Figure 4-1 shows a soldering iron resting in a simple stand. As you can see, this stand keeps the business end of the soldering iron safely elevated away from the work surface.
- Give your soldered joints a few minutes to cool down before you handle them.
- Watch out for the soldering iron’s electrical cord. Obviously, you want to avoid burning the cord with the soldering iron. As ridiculous as it sounds, I did this myself once when I carelessly set the soldering iron aside, directly on top of its own power cord. Fortunately, I noticed my mistake before the soldering iron melted much of the power cord’s insulation.
  
  Make sure the soldering iron’s power cord is placed safely away from your stuff so that you won’t bump it as you work, knocking it out of its stand and perhaps causing a burn.
- Be sure to wear eye protection when you solder. As solder melts, it occasionally boils and splatters little globules of hot solder through the air. You really don’t want molten metal anywhere near your eyes.
Electronics — and especially soldering — can also create a chemical hazard. When you solder, small amounts of lead are released into the air. Therefore:
- Always work in a well-ventilated place.
- Wash your hands after you work with solder or any other electronic components before you touch your face, mouth, nose, or eyes. Small amounts of lead and potentially other toxic substances are bound to get on your hands. It’s best to wash them frequently to keep whatever gunk they pick up from getting into your body.
- Keep your soldering tools away from children. Young children and pets love to stick things in their mouths. If you leave solder or little electronic parts like resistors or diodes sitting loose on top of your workbench, your kids or pets may decide to make a meal of them, so keep such things safely stored in boxes or cabinets and, if possible, keep your entire work area safely off limits and behind closed doors.
- Don’t get into the habit of sticking parts into your mouth to hold them while you’re working. As crazy as it sounds, I’ve seen people hold a dozen resistors in their mouth while soldering each one into a printed circuit board. That’s definitely a bad idea.
Working with sharp tools such as knives, wire cutters, and power drills creates a risk of cutting injury. Therefore:
- Think before you cut. Make sure you know exactly where you want to make the cut, and make sure you know exactly where all your fingers are before you start the cut.
- Let the tool do the work. Don’t apply excessive force to coerce a tool into making a bigger, deeper, or wider cut than it’s designed to do.
- Keep your tools sharp. Working with dull tools causes you to use extra force, which often results in the tool slipping and finding itself lodged in your finger.
- Remove jewelry such as rings, wristwatches, and long dangling necklaces before you start — especially if you’re working with power tools.
- Wear safety goggles whenever you’re cutting, sawing, or drilling. Little pieces of the work or blade can easily break off and hit you in the face. Add bits of insulation, copper wire, and broken drill bits to the growing list of things you don’t want in your eyes.

FIGURE 4-1: A soldering iron resting on a stand.

Protecting Your Stuff from Static Discharges

Static electricity — more properly called electrostatic charge — results when electric charges (that is, voltage) builds up in the absence of a circuit that allows current to flow. Your own body is frequently the carrier of static charge, which can be created by a variety of causes. The most common is friction that results from simple things such as walking across a carpet. Your clothes can also pick up static charge, and usually do when you toss them around in a clothes dryer.

Static charge accumulated in your body usually discharges itself over time. However, if you touch a conductor — such as a brass doorknob — while you’re charged up, the charge will dissipate itself quickly in an annoying shock.

If the conductor happens to be a sensitive electronic component such as a transistor or an integrated circuit rather than a brass doorknob, the discharge can be more than annoying; it can fry the innards of the component, rendering it useless for your projects. For this reason, it’s wise to protect your stuff from static discharge when you work on your electronic projects. The easiest way to do that is to make sure you’re properly discharged before you start your work. If you have a metal workbench or a large metal tool such as a drill press or grinder near your workbench, simply reach out and touch it after you’ve settled in to your seat and before you begin your work.

A more reliable way to protect your gear from static discharge is to wear a special antistatic wristband on one wrist, as shown in Figure 4-2 . Wear the wristband tightly so that it’s in good solid contact with your skin all the way around your wrist. Then, plug the alligator clip into a metal surface such as your workbench frame or that nearby drill press.

For best results, the alligator clip on your antistatic wristband should be connected to a proper earth ground . To create a proper earth ground, clamp a long length of wire to a metal water pipe. The wire should be long enough to reach from the pipe to your workbench. Carefully route the wire from the pipe to your workbench, strip off an inch or so of insulation, and staple or clamp the wire to the workbench, leaving the stripped end free so you can attach the alligator clip from your antistatic wristband to it. (Note that this technique works only if the building uses metal pipes throughout. If the building uses plastic pipe, the water-pipe won’t provide a proper ground.)

An often-recommended way to connect the wristband to an earth ground is to connect it to the ground receptacle of a properly grounded electrical outlet. I’m definitely not a fan of this method, as the key to its operation lies in the term “properly grounded electrical outlet.” All it takes is one stupid wiring mistake, or one wire shaken loose by a sonic boom or a mild earthquake, and suddenly that ground wire might not be a ground wire anymore — it might be energized. Call me paranoid if you wish, but there’s no way I can recommend strapping a conductor around your wrist and then plugging it into an electrical outlet.