Chapter 4
Staying Safe
In This Chapter
Understanding the risks of electric shock
Protecting yourself from the perils of stray electricity
Safeguarding your gear from static electricity
The possibility of electric shock is always present whenever you work with electricity, but don’t forget the other potential dangers as well. If you’re not careful, you can start a fire or otherwise injure yourself or other people.
In this chapter we explain how to keep yourself safe while experimenting with electronics. We discuss the different dangers that electricity poses to you and to your equipment. Please read and heed every piece of advice we give.
Facing the Shocking Truth about Electrical Dangers
The simple fact is that an electric shock, if strong enough, can kill you. So whenever you work with electricity, ensure that you take every precaution you can to avoid being the recipient of a shock strong enough to do you damage.
Thousands of people die every year from accidental electrocutions. Many of those accidents are industrial or weather-related, in which people come into contact with downed power lines. But many are completely avoidable accidents that happen in the home. In the sections that follow, we give you specific guidelines for avoiding accidental electrocution.
Heeding the warning: Household electrical current can kill you!
One of our favourite bits from the TV series Father Ted comes when he and Father Dougal wait for news on the condition of their parochial house guest Father Stone, the most boring priest in the world, who’s struck by lightning while playing crazy golf in a thunder storm:
Father Dougal: Who’d have thought being hit by lightning would land you in hospital?
Father Ted: What? What are you talking about? Of course it can land you in hospital.
Father Dougal: Well it’s not usually serious is it Ted. I mean, I was hit by lightning a few times and I never had to go to hospital.
Father Ted: Yes Dougal, but you’re different from most people. All that happened to you was that balloons kept sticking to you.
You aren’t Father Dougal, you aren’t strangely immune and you aren’t stupid. Electricity can kill you, whether it’s a lightning strike or a shock from the household mains, and we hope we don’t really need to tell you that:
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 need to be extra careful whenever you plug or unplug something into or from an electrical outlet and whenever you change a light bulb. Specifically, 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.
Discard any extension cords that become frayed or damaged in any way. When the insulation begins to rub off an extension cord, the shock hazard is all too real.
Never perform electrical wiring work while the circuit is energised. 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. To be even surer, switch off the whole of the supply.
People die every year because they think they can be careful enough to safely work with live power.
Never work on an alternating current (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 special precautions when working near AC circuits powered by household mains electricity. We talk about using AC circuits in Book IV and say more about AC safety there.
Understanding that even relatively small voltages can hurt you
Most of the projects in this book work with AA batteries, usually four of them tied together to produce a total of 6 V. That’s not enough voltage to do serious harm. Even if you do get a shock with 6 V, you probably barely feel it.
You can, however, injure yourself with voltages even as low as 6 V. If you create accidentally a short circuit between the two poles of a battery, a lot of current flows very quickly. The likely result is that the wire connecting the two ends of the battery gets extremely hot and the battery itself heats up. This heat can be enough to inflict a nasty burn.
If the racing current goes unchecked, a possibility exists that the battery may explode. Trust us; you don’t want to be nearby if that happens and you really don’t want to make a trip to A&E to have fragments of an exploded battery removed from your eyes.
As a result of this danger, 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, and always remove the batteries before you walk away from your workbench.
Touch the batteries periodically with your finger to ensure that they aren’t hot, and if they’re getting warm, remove the batteries and recheck your circuit to make sure that you haven’t made a wiring mistake.
Remove the batteries and recheck your circuit if you smell anything burning.
Never use Lithium cells – those little flat batteries that you sometimes find in portable gadgets. Lithium cells can explode in circuits without special precautions. Standard NiCd batteries are safer but be careful that other voltage sources in a circuit don’t charge the batteries accidentally.
Wear protective eyewear at all times to protect yourself against exploding batteries, and remember that under the right circumstances other components can explode as well!
Staying safe by staying dry
Water and electricity is an extremely bad combination, because water is an excellent conductor of electricity and it flows everywhere (read the nearby sidebar ‘Wading into the subject of water and electricity’ for more).
Always avoid water when working with electrical current. Here are a few safety tips to bear in mind:
Make sure that the floor is dry and never 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 well before working with electrical current, because 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.
Realising that voltage can hide in unexpected places
One of the biggest shock risks in electronics comes from voltages that you don’t expect to be present. Keeping your eye on the voltages you know about is easy enough, 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 V batteries, much larger voltages may be present at specific points within your circuit.
In addition, some electrical devices can store electric charge long after you disconnect the power from your circuit. The most notorious device with this characteristic is the capacitor, which alternately builds up and then releases electrical charges.
Remain 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. But if your circuit has capacitors the size of batteries, be very careful when working around them. Such capacitors can hold large charges long after the power is cut off.
Here are some safety points concerning capacitors:
You commonly find large capacitors 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 that it’s not working.
You often find high-voltage capacitors in flash cameras. Even though the battery may be just 1.5 V, the capacitor that drives the flash unit may well be holding a charge at 300 V or more.
Always discharge the capacitor before working on a circuit that contains one. You can discharge small capacitors by shorting out their leads with the blade of a screwdriver. Make sure that 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.
Discharge larger capacitors by connecting their leads to a lamp or a large resistor. The easiest way is to wire up a lamp holder to a pair of crocodile clips, screw a lamp into the lamp holder and then carefully connect the clips to the capacitor leads. If the capacitor is holding a charge, the lamp glows 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.
Lamp is the engineering term for what everyone else calls a ‘bulb’. If you try to buy light bulbs in your local hardware shop by asking for lamps, the assistant probably shows you standard lamps or table lamps. Mention bulbs to electrical or electronics engineers, however, and they’re more likely to think that you’re talking about something you plant in the garden.
Considering Other Ways to Stay Safe
Electric shock (which we discuss in the earlier ‘Facing the Shocking Truth about Electrical Dangers’ section) isn’t the only danger you encounter when you work with electronics. This section summarises a few of the other risks you can be exposed to and describes the precautions to take to minimise those risks:
Soldering poses an obvious fire hazard. If your soldering iron is hot enough to melt solder (we describe the process in this minibook’s Chapter 7), 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 down a hot soldering iron directly on your workbench. Instead, get a soldering iron stand to hold the soldering iron safely 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.
Figure 4-1: A soldering iron resting on a stand.
• 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, putting a hot iron down on its own cord, or in such a way that it can slip onto its own cord, is an easy mistake to make.
Make sure that the soldering iron’s power cord is placed safely away from your stuff so that you can’t bump it as you work, knocking it out of its stand and perhaps causing a nasty 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 create a chemical hazard. When you solder, fumes are released into the air. Therefore:
• Always work in a well-ventilated place.
• Wash your hands after working with solder or any other electronic components before you touch your face, mouth, nose or eyes. Small amounts of substances are bound to get on your hands. 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 animals) love to stick things in their mouths. If you leave solder or little electronic parts, such as resistors or diodes, sitting loose on top of your workbench, youngsters 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. We’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 injury:
• Think before you cut. Make sure that you know exactly where you want to make the cut and exactly where all your fingers are before you start cutting.
• 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 lodging in your finger.
• Remove jewellery 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.
Keeping Safety Equipment on Hand
In spite of every precaution you take, accidents are bound to happen as you work with electronics. Other than preventing an accident from happening in the first place, the best strategy for dealing with one is to act like a scout and ‘be prepared’.
Keep the following items nearby whenever you’re working with electronics:
Fire extinguisher: So you can quickly put out any fire that may start before it gets out of hand.
First-aid kit: For treating small cuts and abrasions as well as small burns. The kit should include bandages, antibacterial creams or sprays, and burn ointments.
Friend: A friend could get you help in case you get shocked.
Phone: So that you can call for assistance in case something goes seriously wrong.
Protecting Your Equipment from Static Discharges
Static electricity – more properly called electrostatic charge – results when electric charge (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 from simple activities such as walking across a carpet. Your clothes can also pick up static charge, and usually do when they’re tossed them around in a tumble 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 dissipates itself quickly in an annoying shock.
If the conductor happens to be a sensitive electronic component, such as a transistor or an integrated circuit, the discharge can be more than annoying; it can fry the innards of the component, rendering it useless for your projects. For this reason, you need to protect your stuff from static discharge when working on your electronic projects.
The easiest way to do so is to make sure that 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’re settled in your seat and before you begin 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 crocodile clip into a metal surface such as your workbench frame or a nearby drill press.
Figure 4-2: An antistatic wristband.
For best results, the crocodile clip on your antistatic wristband needs to be connected to a proper earth ground, by clamping a long length of wire (long enough to reach from the pipe to your workbench) to a metal water pipe. Carefully route the wire from the pipe to your workbench, strip off a couple of centimetres or so of insulation, and staple or clamp the wire to the workbench, leaving the stripped end free so that you can attach the crocodile clip from your antistatic wristband to it. (Note that this technique works only if the building uses metal pipes throughout. If it uses plastic pipes, the water pipe doesn’t provide a proper ground.)
Some people suggest connecting the wristband to an earth ground using the ground receptacle of a properly grounded electrical outlet. We’re definitely not fans of this method, because the key to its operation lies in the term ‘properly grounded electrical outlet’. One stupid wiring mistake, or one wire that works loose, and suddenly that ground wire may not be a ground wire anymore – it may be energised. Call us paranoid if you like, but we can’t possibly recommend strapping a conductor around your wrist and then plugging it into an electrical outlet.