Switches and Receptacles

We use them every day, but we don’t think about them much. This is a good indication of the reliability of switches and receptacles. A bathroom light switch, for example, might be clicked on and off 10 times a day (depending on the size of your family). That’s a few thousand clicks each year, and the switch keeps going and going. If only our computers and operating systems were that reliable. A switch controls the flow of electricity between a source and an end device such as a light fixture. In a standard modern light switch, a metal arm inside the switch connects the two screw terminals to which the black, or hot, wires are connected. In the “Off” position, this arm moves out of the way and cuts off the flow of electricity along the conductors.
Receptacles don’t face as much mechanical wear and tear as a switch undergoes. A common house receptacle is called a duplex receptacle because it can accommodate two plugs. The metal connector between the screw terminals is fixed in place, unlike the movable arm in a switch. Each prong of a plug is held in place by two pieces of spring metal to maintain a solid electrical contact.
Both switches and receptacles can wear out, especially the original ones in an old home.

What you need to know about electrical wire?

Other than a brief foray in the 1970s when aluminum wiring was popular, copper is king when it comes to house wiring. Copper rates high on the conductivity scale. That is, it’s an efficient pathway for an electrical current.

Conductivity Scale
Silver 100%
Copper 98%
Aluminum 61%
Iron 16%
Nickel 7%

In addition to a wire’s conductivity, its size and the type of insulation around the wire affect its ampacity, or the amount of current (in amps) it can carry before it exceeds its temperature rating. The greater its size, as measured in mils, the more current it can conduct.
Every wire size has a maximum current that it can conduct. The following table shows the most common residential wire sizes and their ratings.

Wire Gauge Rating
Gauge Value Ampacity
14 15 amps
12 20 amps
10 30 amps
8 40 amps
6 55 amps

Appliance and lamp cords use No.16 or No.18 wire, which is quite thin. This might lead you to ask, “Well, if thinner wire has a lot of resistance and can heat up easily, but thicker wire can hold more juice without overheating, why don’t we use thicker wire throughout our homes? Wouldn’t that be safer?” This is a reasonable question, and it has two answers: flexibility and cost.

If you try to bend and fit No.8 wire so you can connect it to a light fixture, you’ll come to appreciate the flexibility of smaller wire. Like just about anything else in life, the larger the size, the greater the cost. There’s a reason home-improvement stores periodically have loss-leader sales on No.12 wire but not any of the thicker stuff. Other factors that affect your choice of wire will be discussed in later chapters.

The society of wire and conductors is a very closed one. No amount of politically correct persuasion will convince one gauge of wire to mingle with another. You should not mix No.12 wire with No.14 on the same circuit, for example. Wire must match up with its circuit breakers or fuses; No.14 wire doesn’t go with a 20-amp breaker, so don’t confuse either party by mixing them together. You can install larger wire on a smaller circuit breaker, but you cannot install a smaller wire on a larger circuit breaker.

What is Electrical Resistance?

Everywhere we look in life, we find some form of resistance. For airplanes, it shows up in the form of wind (and maybe an occasional bird or two). Water keeps kayakers afloat, but it also slows them down some. Even the indomitable James Bond in his Aston Martin DB5 had to contend with resistance when his tires hit the road. It would be great if all the electrons in a current could go gliding across a copper wire (or another conductor) free and clear, but pesky resistance prevents them from doing so.

Resistance in a conductor opposes the flow of an electric current. This results in some of the electrical energy changing to heat, which you want to minimize. Hot wires can be dangerous wires. On the other hand, resistance is built into the system to control the strength of the current running through it. You also don’t want your blender getting hit with 50 amps of electricity when you’re mixing a fruit shake. Electrically speaking, resistance is measured in ohms.

Ohm’s Law (Ohm was a German physicist with a great name) basically says that the smaller the wire or conductor, the greater the resistance to a current. If you crank up the amps, you get even more resistance, sometimes to the point of overheating and causing a fire. Loads that require more amps also require larger wire to handle the current flow. If you increase the size of the wire, the resistance goes down, and you get a weaker current with less voltage drop. This is one of the reasons you have several different sizes of wire in your house.

Think of it this way: Imagine that the fire department is putting out a fire in your house.

You’re happy that they’re using a big hose (just as a No.6 or No.10 is a big wire for big jobs). But what if you’re just watering your garden? Then you want to conserve water and avoid flooding the garden. You’ll use a small hose (just as a No.12 or No.14 wire is good for small items such as light fixtures).

Wattage Around the House

How do watts figure into your electrical calculations? It’s simple: They tell you how much stuff you can pile onto one circuit without overloading it. You don’t want to put too much demand on a circuit with too many watt-hungry loads. Some simple math will keep you on the right track.
Watts equal voltage times amps. Let’s say you want to install a new 15-amp circuit so you can add some outlets or lights to your living room and dining room. Because you won’t be running any major appliances (assuming you don’t do your laundry in the living room), this circuit will be running on 120 volts rather than 240. Therefore … 120V X 15A = 1,800 watts

Terrific, you say. I can put in 18 100-watt lights. Actually, you can’t, because you generally figure on running only 80 percent of the maximum load —1,440 watts in this case—but that’s still 14 lights with watts to spare. What if you want to plug in your new window-shattering, guaranteed-to-have-theneighbors-call-the-police music system that needs 1,900 watts all by itself? Time to recalculate. It’s going to need its own private 20-amp circuit before you can crank up Eric Clapton’s original version of “Layla.” By calculating your electrical needs first, you can accurately wire your house once without needing to make adjustments later.

What is Watt?

Watts are one of the measurements you will refer to in your electrical work. Most of us know the term from buying light bulbs (I know, the term should be lamps, but this isn’t an easy one to get away from) as in “Why do we have a shelf full of 60-watt bulbs when I need 100?” A watt is a unit of electrical power. It tells you how much electricity you’re consuming and being billed for by your utility company. This is why you have a meter outside your house recording your usage. A single watt is a minuscule way to measure power usage, so the following larger units of measure are used instead:

• Kilowatt or kw (1 kw = 1,000 watts)
• Megawatt (1 megawatt = 1,000 kw or 1 million watts) You’ve really got some usage problems if your electric bill indicates that you’re in the megawatt range. (Perhaps you have a refrigerated warehouse on your roof.)

What is Ampere?

While Volt measure the force of an electrical current, which is the movement of zillions of electrons. Amperes or amps measure the number of electrons in a current moving past a specific point on a wire or another conductor in a one-second period of time. If you want an exact number, one ampere equals one coulomb of electrical charge moving across a conductor in one second (or 6,250,000,000,000,000,000 electrons per second).Coulombs were named for that fun eighteenth-century French physicist, Charles A. de Coulomb.

If electricity were water, volts would be the speed of the water, and amps would be the amount of water flowing through your hose. A new three- or four-bedroom house often will have a 200-amp service; apartments or small condominiums might only need 100-amp services. Individual fuses and circuit breakers are measured in amperes. That is, they only allow a certain amount of current to pass through before they shut down the current.

What is Voltage?

There are a lot of terms associated with electricity. Different words refer to a current’s strength, the speed at which it travels, and the rate at which it’s consumed. Voltage is a sometimes-misunderstood term that means “electomotive force” or, more simply, electrical “pressure.” Voltage also is the difference in electrical potential between one end of a circuit and the other. In our electrical systems, voltage is measured against the earth, which is at zero potential. In other words, it all starts with the ground under your feet. Voltage gets the electrical ball rolling by giving a push to electric power from your utility’s generator to your house or business.
Long-distance power lines carry huge voltages, from around 155,000 to 765,000 volts. If you hooked your vacuum cleaner up to that kind of power, you’d melt its engine instantly—and possibly yourself as well. You previously read that transformers reduce the voltage before it enters your house. A few hundred thousand volts might sound like fun to your kids, but you should be grateful that you end up with a lot less voltage, thanks to transformers.

What is Grounding?

Now that you know what kind of current you have in your house (and everywhere else), let’s discuss another critical feature—grounding. Your entire electrical system, if it’s up to current code, is grounded for your protection. This literally means that one wire of your electrical system leads back into the earth itself, where it will carry any errant current that could otherwise shock or electrocute you. The earth ends up being a good electrical conductor and a convenient return path for electrons. In fact, the earth is used as a reference point for measuring the voltage in our electrical systems.
A ground wire can be attached to a ground rod that is deeply buried, or it can be a length of copper wire buried near your foundation’s footings. A second physical ground is usually your cold-water supply pipe near your service panel.
Modern house wiring is color-coded so you won’t confuse your hot, neutral, and
ground wires with one another. This coding is standard everywhere—there is no room
for artistic creativity here. The wire colors are …

• Black and red for hot wires
• White for neutral wires
• Bare (unsheathed) copper or green for ground wires

The black, red, white, and green colors refer to the plastic sheathing that contains the wires themselves. If you have an old two-wire system , you won’t have a ground wire. An old knob-and-tube system sheaths both the hot and neutral wires in black, which isn’t exactly user-friendly when you’re trying to distinguish one wire from another. It’s important to understand the difference between the grounding wire and the neutral wire.
The neutral white wire carries the electrical current back to the power source after it’s passed through a load (a ceiling light, a fan, a stereo, and so on).
That’s the nature of an alternating current. The grounding wire, on the other hand, protects the entire system. The neutral wire is more correctly referred to as a grounded conductor. The bare or copper wire is a grounding conductor.

What is AC/DC?

When Thomas Edison and his crew invented a reliable electric light bulb, he followed it up by developing the power systems to run it, rightfully envisioning a future world full of light bulbs. (We usually refer to these as “light bulbs,” but “lamps” actually is the correct term. Bulbs are for planting.) Edison employed direct current (DC), which now is used in battery-operated gadgets in which the current flows from the negative terminal of the battery to the positive terminal. A battery is basically a container of chemicals whose electrochemical reactions produce excess electrons. Our electrical systems use alternating current (AC), which was developed by Edison’s contemporary, George Westinghouse, after he bought up patents from Nikola Tesla and William Stanley. Once again, someone with business sense trumped the scientific minds possessing the money-making ideas. It took Edison, the lampmeister, a few years to go along with this AC business, but he eventually told Westinghouse’s son to let his dad know he was right.
A direct current just means that the electric current flows continuously in one direction and keeps going until it finds something to run such as a radio or a light bulb. An alternating current flows in one direction—say, to a receptacle—and then flows back in the opposite direction. You might be thinking, so what? When was the last time alternating current was discussed on late-night talk shows? Probably never. Alternating current, however, does have some useful, consumer-friendly features such as the following:

• Through a series of transformers, an AC can be increased or decreased in value. (The current can be made stronger or weaker.) This means that, instead of a zillion watts of power heading for your panel box, you’ll get a reduced amount that you actually can use.
• Alternating current is efficiently transported over long-distance power lines.
• It’s easy to convert from AC to DC, but it’s expensive to go from DC to AC.

Staying Current

Electricity doesn’t do us much good if a bunch of errant electrons constantly change orchestras from one conductor to another. We want our electrons to move in a reasonably orderly fashion so they can do our bidding when we turn on the lights. A flow of electricity is called a current, and it’s carried into our homes through wiring from local electric utility companies. New electrical systems have the following three wires coming into your house:
➤ Two black or “hot” wires that carry the current to your service panel
➤ One bare neutral wire for carrying the current back to the power source and to ground An electrical current has a couple of different options, depending on your application.

Going with the Flow

Think back to your high school physics classes and all those diagrams of atoms with electrons spinning around a nucleus. (They’re the drawings that looked like really small solar systems.) Basically, electrons spin around because the protons in the atom’s nucleus carry a positive charge (+) that repels the electrons’ negative charge (–). If enough of the electrons decide to move on, preferably in a more or less uniform stream, we end up with usable electricity.
Electricity comes in several flavors, but the two we’re most familiar with are …
➤ Static electricity, in which the electric charges are stationary.
➤ Dynamic electricity, in which the electric charges are moving in a current.
When you were younger, the main value of static electricity was using it to shock unsuspecting siblings and cousins after you had walked across a carpet. If you didn’t do this when you were a kid, you can always try it at your next holiday dinner. Cats also are good targets, but their revenge usually is a messier affair. Why does the shock occur? Because some electrons like to travel, and they aren’t the most stable subatomic particles. When you walk across a carpet (some are worse than others), you pick up some of these hitchhiking electrons while leaving some of your own positive charges. They have to go somewhere, and your sibling’s finger or a doorknob makes a dandy conductor. If you touch a door frame, nothing happens because wood is a good insulator. That is, it does not allow electrons to easily move through it.
Static electricity is simply an imbalance of positive and negative charges. When you get zapped, you’re just the accountant trying to balance these charges. One place you don’t want to balance these charges, by the way, is with your computer, so you can either …
➤ Touch your metal desk chair before turning on your computer to get rid of any pesky electrons that could affect your computer.
➤ Apply anti-static spray periodically to your carpet so it will have a more positive charge and be less likely to give up its electrons. Static electricity may be annoying, but dynamic electricity is another story altogether.

About Electricity

We use and depend on electricity every single day. All we usually know about it is that it’s buried inside our walls, it runs our lights and VCRs, and we’re billed for it every month or so. Terms such as kilowatt hours, amperage, volts, and current are Greek to most of us. This is probably appropriate because the Greeks first described static electricity about 2,500 years ago. It was discovered that amber would accumulate a negative charge of static electricity when rubbed with sheep’s wool. Not known for a great sense of comedy, this probably became quite the party trick at Greek get-togethers. The word “electricity” has its root in the term electrum, which is Latin for “amber.” Understanding electricity is like understanding cooking: Once you know a bit about sautéing, cooking temperatures, seasonings, and how to make a decent pie crust, you can muddle through meal preparation and come up with more-than-edible results. If you know how electricity is produced and can toss around some vocabulary words, such as alternating current and resistance, you’ll be more comfortable with your electrical work. A task makes more sense when you understand its inner workings. This section isn’t going to give you enough information to challenge a Ph.D. in electrical engineering to a trivia contest at your local Jeopardy theme bar. You will, however, develop a working knowledge of electricity basics and how they apply to your own electrical system