Electricity in your Home

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How does electricity get where you need it?

Electricity in your home is not rocket surgery, but there are some basics and some details that will help you deal with issues on your own, know when to call an electrician, and what to tell her or him when you call. In this introduction to electricity in your home, we'll add enough details about things you may already know and about house wiring issues that affect you everyday - especially on the days when something goes wrong.

Over time, we will add short articles about specific electrical topics to our website. If you would like us to answer your questions about electricity, lighting, telephone, or computer networking in our website's Electrical Education section, email us at TechnologyForTheRestOfUs@onlyconnectelectric.com.


Electricity travels from the generating stations to the neighborhood at very high voltages, as high as 100,000 volts or more. By the time it gets to the wires that come into your home, it's been through several transformers that reduce the voltage to what you need to light a lamp in your living room or run your clothes dryer. What we will do as simply as possible is describe electricity is handled inside your house.

The Service Drop

Most of us have large cables (the service drop) that dangle from a pole at the curb to a hook on your house. If you were to look inside you would see that the cable has two large insulated wires that carry power and a bare wire that provides the "ground" (more about that later). Electricity comes into our homes at 120 and 240 volts.

The service drop connects to wires attached to your home (the service entrance conductors) that lead to your electric meter. We could do without the meter, but the electric company wants to send us a bill. The meter contains a small motor that turns a wheel that you can see move faster when you have more lights or appliances running.

The Service Panel

After the meter, the service entrance conductors continue into your home to the circuit breaker or fuse panel (the service panel) in your basement. The service panel is really where the story of how electricity works in your home begins. Behind the panel cover door or cover, you will find a switch or a fuse at the very top that regulates all of the electricity that comes into your home. Below it, you will see a series of switches (circuit breakers) or fuses that regulate each of the circuits that run through your house.

The Main

In the service panel, the service entrance conductors attach to "the main," a circuit breaker or a set of fuses that protects your entire house. Typically sized from 60 to 200 Amperes, the main shuts off the power to the entire house when you are drawing more power, through every plug, lamp, or appliance than you have available. Without the main to protect you, your wires could get too hot, melting their insulation and igniting nearby wood or other combustibles. If the main keeps tripping, and this rarely happens, it means that you don't have enough power coming into your home.

Circuits and Circuit Breakers

Once the power passes through the main it is divided into individual circuits. In the service panel, the power is divided up and runs through circuit breakers or fuses that protect each of the wires (circuits) that leave the panel to do something useful. A circuit is exactly what it sounds like, a smaller pair of insulated wires, with a ground, that run through your home to a number of outlets, lights, fans, or other appliances. Each circuit is protected by a smaller circuit breaker that is usually safe for only 15 or 20 Amperes.

There are a number of different circuits running through your home; some might power a string of lights or outlets, while others may go to a single large appliance like a stove or the heating system. When there's a problem on one circuit, the breaker turns off the power (trips) on just that one circuit; the rest of the house continues to have electricity to run your lights, TV, computer, heat, and other good things.

When Do Circuit Breakers Trip?

It sounds like a dumb question, but it's not. There are two ways your wiring can get too hot and cause problems: overloads and short-circuits.

If you have an outlet above your kitchen counter, it should be on a 20 Ampere circuit with a 20 Ampere circuit breaker. The wires can safely carry 1920 watts before overheating.

If you run a toaster (often 1200 watts) and a microwave (often 1250 watts) on that circuit at the same time without a circuit breaker, they use 2450 watts: enough to overload the circuit, overheat the wires, and damage the insulation. A 20-Ampere circuit breaker on the line prevents this by slowly warming up with the wires and then saves the day by shutting off the power before the wires get too hot, and preventing damage to their insulation, or the house. It's a pain in the neck that should and can be fixed, but in the meantime, you still have a house.

Another way a circuit breaker can be tripped is if you accidentally drop a kitchen knife on the toaster cord and connect the two wires in the cord. You would have a short-circuit, and you would probably see a spark. When a short circuit occurs, the power goes out through one wire and then back on the other, without ever reaching the toaster. Unlike a toaster, the wires have very little resistance. Suddenly, a huge electrical current flows through the wire. If allowed to continue, it would heat the wire and cause damage very quickly. In this situation, the circuit breaker trips very quickly. Short circuits like this can also occur inside a fan you have plugged in or in the electrical boxes and cables in your walls.

Circuit breakers and fuses are designed to prevent damage or fire from both overloads and short-circuits.

If a particular circuit breaker keeps tripping it probably means that you have too many appliances or lights on that circuit. It may be time to add a new circuit and divide the appliances and lights between the two circuits. It rarely means that you need to increase the power available in your home with an expensive "service upgrade."

If you find that the main fuses are blowing or the main circuit breaker in the panel is tripping, you may need more power than is available to the entire house. Then it's time to investigate whether a service upgrade may be in order.

How good are circuit breakers?

With so much depending on circuit breakers, the natural question is, "How good are circuit breakers?" And if you have an old fashioned fuse box, "Is it necessary to upgrade to a panel with circuit breakers?"

Circuit breakers are very reliable, but they are not perfect. We cannot live safely without them, but like all electrical-mechanical devices, circuit breakers are built in ordinary manufacturing plants. Only a miniscule percentage of them leave the factory defective, but all of them get old. Eventually a few of them don't work so well.

Defective breakers may trip when there's no problem or may fail to trip when there is a problem, but they are typically extremely reliable and absolutely worth using. Fuses, which are much older technology, are less convenient because you have to keep a supply of replacements on hand and change them when they blow. But fuses are much simpler and even more reliable: when there is a problem, they get hot; the lead melts, the circuit is off. So, unless there is something wrong with your fuse box, or the bank with the mortgage money insists, you might not need to replace a fuse box with circuit breakers.

A New Circuit or More Power?

You've probably had a circuit breaker trip at some time. Your cat gnawed through a lamp cord, and poof (that's a technical term), half the lights in your house went off. Everything that went off was on the same circuit. This is one way to understand where each circuit goes in your house, but it is probably not the best way.

Older houses were built for simpler times: fewer electric appliances and very few circuits. All the lights and receptacles on a floor were often on the same circuit. We were recently in a house that had the basement lights and the receptacles in the front hall, living room, and one bedroom on the same circuit.

Even if the service panel was upgraded to 100 or 200 Amperes, the old circuits may have been merely reattached to the new circuit breakers. In other words all of the plugs, lights and appliances in the kitchen may still be on that same 20 amp circuit. All that additional power coming into the service panel won't do any good if you don't split it up into new circuits. And if you add new circuits, odds are you won't need that service upgrade.

This is the big reason why we believe that it is often better to spend your money on getting more circuits than getting more power into the house.

Newer houses often have more circuits that are divided up more sensibly. Keeping lights and receptacles on different circuits means that the overhead light still works when the receptacle circuit goes off. Although it's a tedious task, it is a good idea to make an accurate list of which lights, receptacles, and equipment are controlled by each circuit breaker. A good list will help you figure out what's going on when a circuit breaker trips. And a good list will save you money when you need to call an electrician. You don't him or her to spend a lot of time figuring out what is controlled by each circuit breaker.

What is Grounding, and Why Should i Care About It?

Short circuits happen. Equipment gets old and fails. Microwaves, vacuum cleaners, washing machines, and televisions get old. Trucks bouncing down the street and kids running up and down the stairs jiggle wires loose. Insulation dries out and crumbles, allowing live wires to electrify metal parts. Short-circuits can destroy equipment and create dangerous situations. Grounding reduces the chances of danger.

An example to make the value of grounding a little clearer: Look at your microwave; it has a 3-prong plug, with an "equipment grounding wire." If a wire inside your microwave jiggles loose or the insulation melts, a live wire may touch the metal appliance case. If you now touch the metal case and the stove or a faucet at the same time, you can receive a bad shock.

To prevent this shock, the grounding wire from the cord is attached to the metal case and to the grounding terminal (the round hole) in the wall plug. The grounding terminal in the outlet connects to a grounding wire that goes back to the service panel. The grounding wire provides a low-resistance path for electricity to get back to the panel. allowing large amounts of current to flow through the circuit and trip the circuit breaker.

The house doesn't burn down, and you don't touch a live metal case and get injured. The 3-wire grounding plug and the 3-hole grounding receptacle save the day.

On the other hand, very few, if any, of the lamps in your house have 3-prong plugs. Take a look around. On your kitchen counter, some appliances do and others don't. Those with 2-prog plugs cannot connect the live metal case to the house wiring: in this situation, replacing a 2-hole receptacle with a 3-hole grounding outlet offers no additional protection.

What are those buttons on my bathroom receptacle?

In some situations, grounding plugs and receptacles do not provide the edge of safety you need. The solution is a ground fault receptacle (Ground Fault Circuit Interrupter-GFCI) that provides extra and faster protection. The buttons are for testing the GFCI and then resetting it.

We've all heard about the dangers of the hair dryer that falls into the bath water. As we have learned from early childhood water and electricity don't mix. When a hair dryer falls into the water, some of the current continues to travel back through the cord to the receptacle in the normal way, but some of it may "leak" and flow through the water to the pipes and back to the ground (the real earth ground). GFCIs are designed to detect the tiniest amount current leakage and shut off the power extremely quickly. In new installations, they are required in kitchens, bathrooms, basements, garages, and outside your house.

If you are in the tub, some of that current may flow through you-not a great idea. The problem is that very small amounts of current flowing across your heart can destroy the normal rhythms of the heart. Because there is no huge surge of electricity, the circuit breaker may not trip quickly enough, or not at all.

The same danger exists when your microwave's metal case get livened up. If you touch the microwave and put your other hand on the stove or a faucet, you can get livened up along with it. But you may not stay alive for long.

GFCIs are designed to detect the tiniest amount current leakage (in this case, through you) and shut off the power extremely quickly. In new installations, they are required in kitchens, bathrooms, basements, garages, and outside your house.

When should I call an electrician?

Safety First: the emergencies. You plug in a radio and you see sparks. You go to turn on a light, and the switch plate seems very hot. You cannot get the thermostat to turn on the heat. Call for help right away.

You turn on a light switch; nothing happens, and then you notice that three other rooms are also dark. So you turn the switch back off, get out a flashlight, and reset the circuit breaker or change the fuse. Still nothing. You remove the light bulbs from the ceiling fixture and unplug everything on the circuit; reset the breaker again. Still nothing. It's time to talk with an electrician for advice. If all goes well, you may be able to track down the problem and maybe fix it. Last resort, you need a house call.

Safety Second: the dangerous inconveniences. The circuit breaker keeps tripping when you forget and use the toaster and the coffee maker at the same time. There are extension cords running under the living room rug because there's no outlet near the TV. Your new treadmill requires a 20 Ampere circuit, and you need to run an extension cord to the closest 20 Amp outlet, two rooms away. You've tripped on the kids' toys on the unlit basement steps more than once; one of these times, you're going to get hurt. Not necessarily cause for an immediate call for help, but it's time for a temporary fix and thinking about a permanent improvement.

Safety Third: comfort and convenience. Your fourth grader wants a computer in her room for homework (and IM'ing, of course); you need a wireless connection to your internet modem. You'd really like a ceiling fan on the porch. You can't use your new heavy-duty drill to mount shelves in the living room because all the outlets have two holes and no ground. Wouldn't it be nice (and cheaper to run) if the outdoor lights had motion detectors? New light fixtures that make the kitchen look a bit more modern or maybe bright enough to read the morning paper? And then there's always the luxury of central air conditioning or home theater.

Only rarely does an improvement require more power to the house and the dreaded, but popular and expensive, service upgrade. There's usually a circuit than can support the new installations. Powering up the enclosed porch or a home theater may need a new circuit and breaker in the panel, but we're not talking about rewiring your whole house to get another light.

Still have questions?

We're always looking to answer your questions about electricity and any related topic. Call us any time; we'd love to talk and maybe use your question as the basis of an article in the coming ONLY CONNECT "Technology for the Rest of Us" section.

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