Know Your Circuits with a Circuit Map

Electricians follow the minimalist school of writing: They write as little as possible when listing the circuits on the form inside the service panel door. An electrician will write “Lighting circuits,” for example, across the space designating one or two specific breakers. That’s all well and good, but a more useful description would say, “Ceiling lights in master bedroom and north bedroom, in second-floor hallway, and at top of stairs.” These written descriptions need more room than most factory-supplied lists provide, unless the writing is very small.

In a new house, the electrician’s list usually is adequate because the wiring is so straightforward. In an old house, however, the list needs to be more specific, especially if past homeowners have added their own electrical marks when they lived in your home. Every owner has different needs, and they manifest themselves with receptacles, lights, and switches in places that will make no apparent sense to you but are perfectly logical for someone else. These include lights in crawl spaces, switches on attic rafters, and receptacles in closets. You don’t need to know their history, but you should know which fuse or circuit breaker controls them, especially if they are tied in to the middle of a circuit and can potentially cause problems. Drawing your own circuit map can be done alone, but it is best done with some helping hands. To come up with your map, you’ll need the following:

• Paper and pen for recording
• Lights and radios to plug into receptacles
• Extra people spread around your house

Circuits and Runs

Circuits can be divided by type:

• General-purpose or lighting circuits
• Dedicated circuits
• Small-appliance circuits

Lighting circuits include most receptacles in living areas other than the kitchen, bathrooms, and workrooms. This is appropriate for most receptacles because we generally use them for small loads such as floor and table lamps or clock radios. Some receptacles will only be used for night-lights; others might rarely or never be used. Even light fixtures have varying loads depending on the wattage of their lamps. They can vary from 25 watts to 150 watts.

What happens when you plug in something larger such as a room air conditioner? What if you have a water heater or an electric range that also requires large amounts of current? These loads call for dedicated circuits, which are so-named because they only supply power to one specific load.
Dedicated circuits include those for …

• Major appliances.
• Refrigerators.
• Computers.

It’s easy to understand why a major appliance needs a dedicated circuit, but what about refrigerators and computers? Even a large refrigerator-freezer combination is rated at about 500 to 700 watts, and a computer is far less. (My notebook PC is a minuscule 36 watts.) These fall into a different category of dedicated circuits that aren’t based on a demand for electrical current but on their specific activity. It isn’t critical for your refrigerator to be on its own circuit from a power-demand standpoint, but if another load somewhere else on the circuit’s run trips the entire circuit, your refrigerator will shut down, and you will be looking at a lot of spoiled food. Some jurisdictions codes require that the refrigerator be on a dedicated circuit.

Computers don’t store food, but they do store your data. Most people readily agree that we should back up and save our documents and spreadsheets while we’re working on them, but then we cheerfully continue working without doing either.

Amps, Watts, and Wire Gauge Working Together

You remember that amps, or amperes, are a measure of an electrical current’s strength or flow. A watt measures the electrical power itself. That is, it measures the amount of electricity consumed by an appliance or another fixture as it converts the electricity into something useful to us. A circuit is sized to allow a certain amount of electricity to run to a given number of loads.

The loads are measured in watts, which is why you can only have a certain number of receptacles and lights on a circuit. Too many running at once demands more juice than the circuit can safely provide before a protective device in the form of a circuit breaker or fuse steps in like a responsible bartender and cuts you off.

The amount of current carried to the various loads also is determined by the size of the wire running between the service panel and the loads. If your wire is too small for the amount of current the load is demanding, it will have a high resistance and will overheat. This is okay for the heating element in your toaster but not for your house wiring. A 20-amp circuit, which usually runs small appliances, requires No.12 wire. Many electricians recommend No.12 wire as the minimum size wire for residential use, even though the code accepts No.14 wire as the minimum-size conductor for branch circuit wiring.

Branching Out to Break Up the Load

You could connect all of your 120-volt electrical loads—lights, bedroom receptacles, the refrigerator, and so on—to one big circuit breaker, and they would still function. Replacing a broken switch or installing a new light fixture then would mean turning off all the power to the house rather than just the power to one particular room. If your housecleaning service trips this giant breaker with a new 55-horsepower industrial vacuum cleaner while you are out of town and is afraid to reset it, you can kiss that frozen Copper River salmon in the freezer good-bye.
Electrical current is broken down into individual circuits—called branch circuits—for safety and convenience. You don’t want the entire house to go dark because a GFCI in the kitchen tripped due to a faulty appliance. Each circuit is designed to carry a certain amperage and to provide enough current to meet the wattage demands of receptacles, lights, and appliances. The following figure shows a standard residential distribution of circuits.
A circuit is laid out logically, or at least it should be. This means that a 15-amp lighting circuit will control lights in, say, three continuous rooms rather than in three rooms at opposite corners and on different floors of the house. Several forces work together to help a circuit do its job safely.

Understanding Electrical Panels

Every electrician has favorite electrical components to recommend, and this includes service panels. Electricians also have panels that they avoid and existing, older panels that they recommend tearing out yesterday if not sooner. This is touchy ground, and anything I or the electricians I have worked with recommend will be subject to criticism in some quarters. With that caveat, I can recommend the following guidelines for choosing a panel:

• You get what you pay for, so skip the low-end panels.
• Ask as many electricians, electrical suppliers, and builders of high-end homes as you can what panel they recommend; one or two names should keep coming up.
• Buy the best panels made by your manufacturer of choice rather than lower-end units made to compete with similar low-end units from chain discount stores.

Consider what a panel does: It acts as the major line of defense in the event of an electrical problem. You want the best panel possible rather than the most basic. They all will be UL-approved, but it’s better to go with a panel that will meet higher standards than the bare minimum. You wouldn’t buy the cheapest brakes for the family minivan, and this is the same attitude you should take with your electrical panel. What does my electrician recommend? He uses the Square D QO panel. Others recommend Cutler-Hammer or Siemens. All of these are reliable brand names that will serve you well.

The More Power the Better

Harry Truman once made a comment about fully equipped armed forces, saying something like, “If we’ve got ’em, then we won’t have to use ’em.” He figured the more power the country had, the more of a deterrent it would be to future aggressors (if only he’d been right). He was on to something about power, though: It’s better to have plenty of it than to not have enough. The same is true with your electrical system. There is nothing wasteful or ecologically sinful about having a minimum 200-amp service in your house. No one says you have to use all that electricity all the time or even ever.

Heed the Boy Scout motto: Be prepared! None of us knows what the future will bring, except maybe dial-up psychics: They know your call will bring them $2.95 a minute. Everything else is a roll of the dice. You might add a second story to your house, set up a woodworking shop in the basement, or double the size of your kitchen. You even could add a casino extension off your garage if your state legislature decides that home-based gambling operations are more in keeping with its ideas about family values. Any and all of these possibilities require electric power. If you’re replacing your current system, think more rather than less because, in this case, less is definitely not more.

The Main Shutoff

Fuse boxes and service panels both have some kind of main shutoff mechanism, and you should know how to use it. The NEC says that you cannot have more than six disconnects—no more than six fuses, breakers, or levers of some kind—to turn off the service. Fuse boxes usually have either a single pulldown handle or two 50-amp pullout fuse holders to disconnect the service.
In a service panel, you will have either a main breaker or a series of breakers in the top half of some older panels that, when shut off, will disconnect the service. Remember, even with the breakers shutoff or the fuses removed, without the meter removed from the meter socket, the panel is still hot where the large wires come in from outside your house.

In case of an emergency in which you must get the power off quickly and cannot identify the specific fuse or breaker, the main shutoff will do the job. Keep in mind that your entire house can go dark. Be sure to have a flashlight close to your fuse box or service panel.