Homeowner’s safety and efficiency guide to electricity and wiring

As a homeowner, you come in contact with electrical circuits on a daily basis. Turn the lights on. Grab milk from the fridge. Tune in to your favourite station to catch the news over breakfast. Without thinking of it, you’ve probably controlled a few dozen circuits before you pull out of the driveway! Good job, Mr. Electricity Master!

Now before you crown yourself Lord Sparky or Emperor Gigawatt, a question; do you have any idea how the electrical circuits in your home actually work? Why you have to flip those pesky circuit breakers, or why the stereo salesman keeps trying to stick an expensive surge protector in the basket every time you buy an appliance? Most people don’t, besides what they forgot to remember from that summer camp merit badge. Thought you were the only one who slept through those lectures, eh?

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If you don’t know your watts from your ohms, this guide is for you. And even if you know a few electric basics (Have 10 imaginary internet points if you can say for sure, without google or phoning a friend, what standard line voltage is) you can learn some new safety tips and perhaps a trick or two to make your home more energy-efficient.

The electricity basics

An electrician in Voorhees said that when thinking about electricity, there are three important values to know: Watts, Ohms, and Volts. You will find the maximum safe value for each listed on things like extension cords and light fixtures. I’ll explain electricity using the analogy of a water pipe. This analogy is likely to make any electrical engineers reading begin to babble about electrons till the short circuit, but it’s a great functional explanation that requires no knowledge of physics.


Volts are a measure of electrical potential. Energy is pushed from the source at a rate expressed in volts. Volts are like water pressure. Power lines in the street are high-voltage, like water from a fire hydrant. Home electricity comes in 120v for general use, which is the equivalent of a garden hose–good for most general tasks. Some special equipment, like pool pumps or laundry machines, require more power and get 240v–the electrical version of a pressure washer.

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Within your home, many devices will reduce the voltage even more. A computer may only need 24v, while a cellphone charger may only use 5 volts. Their charges will step-down the power from your wall to a lower pressure that so it doesn’t fry the delicate internal electronics.

For efficient delivery, power from the main generator station to local substations flows at extreme voltages, usually around 150,000 volts. Voltage is reduced at several sub-stations until it reaches around 3,000 volts, and pole-mounted transformers finally reduce that to 120v or 240v before final delivery to your home’s junction box.


Sticking with the water analogy, Amperage (also called current) is the volume of water flowing through a pipe. While danger signs often say “Danger–High Voltage”, amps are the real killer. The zap you feel from static shock can be up to 25,000 volts, but there is almost no current. On the other hand, sustained contact with just 30 milliamps (mA) can cause shock, 50 mA causes muscle failure and possible death, and any current over 1,000 mA (or 1 amp) will cause tissue burns, and likely fatal electrocution.

Remember how I said less than 1 amp can kill? Well, guess how many amps your home electrical system can supply.

The correct answer? The main service panel in your home is supplied with 80 to 200 amps, depending on the size and age of your home. Each individual circuit (like the lights in your bedroom, or the sockets in your kitchen) can draw 10 to 20 amps before a circuit breaker or fuse cuts power.

There are a lot of protective devices downstream from the main service panel, so a mistake is more likely to cause a nasty shock than death. But once you get to the main service panel, any mistakes will expose you to the full 200 amps, which is a death sentence if you accidentally touch live wires.


Watts is a measure of how much power is available overall. It’s taken by multiplying the voltage (pressure behind the electricity) with the amperage (total available current). The standard house current is 110 volts AC, so if a toaster claims to draw 1100 watts, that microwave uses 10 amps at its highest output. While you don’t need to worry too much about watts in most home applications, you should know that more watts mean more available power. You will often find sound systems and  12v garden transformers measured in output by watts.

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Breakers and fuses and GFCI, oh my!

Let’s follow the yellow brick road–to electrical safety! As you do basic home maintenance, there are three vital safety components to any electrical system that you should know about.


Fuses are sacrificial components inserted into a circuit to prevent dangerous conditions which could lead to a fire. Wires heat up as they carry electricity, and if you try to run more amps than that wire is safely rated for, the wire can heat up like an electric torch, melting its casing and starting a fire. Fuses stop this process by making the current in a circuit pass through a silver element rated to melt at a given amperage. This value is slightly higher than the sustained current rating of the circuit, so it won’t blow after a quick power surge from plugging in a large appliance.

Fuses were the only safety device in many home’s electrical wiring for decades. When they blew out, they had to be replaced. Frugal homeowners sometimes replaced missing fuses with a penny, a dangerous practice that has caused hundreds of home fires. Fuse boxes can be found in many homes built before the 1960s, and many modern appliances still have small replaceable fuses. Replacing a 50¢ fuse is cheaper than replacing a $2000 TV in a power surge.

Circuit breakers

Circuit breakers, much like fuses, cut off power to a specific circuit when current exceeds a safe limit, and your whole home is protected by a breaker that cuts power to everything when the total load on all circuits exceeds a safe limit. Breakers can last more than 20 years in service and are designed to fail closed, so a faulty breaker won’t cause a fire.

In high-voltage situations, fuses were inadequate to safely cut power in case of a short circuit, and mechanical switches created dangerous arcs of high voltage that could be deadly for power company employees. Around 1910 American power plants began testing automatic circuit breakers in oil baths to eliminate the deadly spark. These designs improved consistently, acting quicker and fitting in smaller form factors. By the late 1940s circuit breakers had been miniaturized for use in warplanes and armored vehicles, and post-war engineers began testing them as replacements for disposable fuses in-home service panels. They were safer than fuses, and by 1965, new homes were being built with circuit breaker panels, while old homes were often retrofitted by new owners.


While circuit breakers and fuses protect the electrical system from overloading, they don’t do much to protect residents from electrocution. That’s where GFCI switches come in. You have probably seen them; sockets with a black or red reset button, often found in kitchens and bathrooms.

These are Ground Fault Circuit Interrupters. They are designed to monitor the voltage on the live and ground wires in a circuit. Normally, these should be balanced. When one voltage drops suddenly but the other doesn’t, that’s a sign that either a cable has been cut or there is a short circuit. This would also be how the voltage would behave if someone touched live wires and was being electrocuted.

Within a second of detecting a fault, the GFCI cuts power to that circuit. This technology is cheap and reliable and saves thousands of lives, especially those of inquisitive children who might stick things into sockets or animals who bite into live wires.

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Surge protectors

Surge protectors are important to protect expensive electronics. An electrical surge is a sudden spike in the potential energy (volts) running through a circuit. A lot of people associate these with lighting strikes, but the insulation and safeguards in modern power delivery make a lightning-strike surge rare. Most damaging surges are caused by the restoration of power after lines go down in a storm. Heavy equipment like elevator motors and air-conditioners can also cause small power surges.

A surge can send the voltage in the lines (normally 0v to 169v) as high as 25,000 volts, for less than a second. Delicate solid-state circuitry exposed to the surge would be fried instantly, and even more resilient electro-mechanical motors and relays can have their windings burned out. Surge-protectors divert over-voltage to prevent this damage and often include a fast-acting circuit breaker as well for extra protection. The element that absorbs over-voltage deteriorates after each use, and you should generally replace a surge protector every ten years.

Home wiring 101

Your home wiring consists of a series of separate circuits connected to the main service panel. The main panel receives high-amp service and splits that between all of your home’s circuits. Most circuits will contain a mix of wall outlets and light fixtures, while heavy appliances (like a refrigerator or electric range) often have a dedicated circuit.

When you plug in an appliance or switch on a lamp, it will draw current from its circuit. For safety, most circuits are capped at 15 or 20 amps. If you try to draw more current, a breaker will trip on the main service panel.

Even if you don’t overload a single circuit, total home use can also cause a breaker to trip if all circuits combined begin to draw more than 120 to 150 amps.

A final word on electrical safety

Electricity can be fun, powerful…and very, very dangerous. It’s good to have an understanding of how your home’s electrical system works. Being able to self-diagnose a tripped circuit breaker or change out a light fixture can save you thousands of dollars over the lifetime of your home. Always remember to turn off power at the main service panel before any kind of wiring project, even something as simple as a ceiling fan of new track lighting.

There are plenty of times when an electrician absolutely must be called. Problems with your main service panel, sparking, or damaged wires and any major rewiring should only be done by a licensed professional. Saving a hundred dollars on a service call is never worth the risk to the lives of everyone in your home if bad wiring starts a fire. And if amateur wiring by an unlicensed person causes a house fire, most insurance policies will not cover the damage.

About the author

Jennifer Bell is a freelance writer, blogger, dog-enthusiast and avid beachgoer operating out of Southern New Jersey.

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