Get to Know Your Home's Electrical System
Your home’s electrical system is more than just a bunch of wires – it’s a complex system, carefully designed to deliver all the power you need for modern life in the safest way possible. Knowing how your home’s electrical system works will help you be a more “empowered” homeowner.
Electrical System Components
The electrical system consists of the line from the pole, a meter where electrical usage is tallied, a main circuit breaker panel (sometimes called “load centers” and, in older homes, fuse panels), separate wiring circuits to all the rooms in the home, outlets, light fixture boxes, and various hard-wired appliances.
The main line typically comes off a pole (but can also be buried underground) to the house where it connects to the meter. Meters are typically installed on the exterior of the home, where they can be read by utility company meter-readers. Most meters are mechanical, with a spinning wheel and mechanical display of numbers. Some newer meters are digital, showing a display on an LCD screen. The meter tallies the amount of electricity used in a home in units of kilowatt hours (kWh). The total increase in the number of kWh from one month to the next is the number used by the electric utility for your bill.
Mike Ashenfelter, Safe Electricity Advisory Board Member adds, “Most meters work only one way, adding up electricity flowing into a home. Some “smart meters,” used on homes which generate renewable energy from wind or solar, will count electricity flowing both into and out of a home. This allows homeowners generating renewable energy to sell excess renewable electricity back to the electric utility.”
The Main Breaker Panel
While it is possible to install a weather-proof main breaker panel, most main breaker panels are installed inside the home. When the main electric supply line leaves the meter, it enters the home and arrives next at the main breaker panel at the main circuit breaker.
The maximum amount of electricity that a home can use at one time is dictated by the size of the main breaker. The breaker is a type of switch, set to flip off in case of an overload in the home, reducing the risk of fire or electrocution. Most modern homes will have 200 amp (short for amperage) service, while an older home might only have 100 amp service and a larger home 400 amp service. If you’re curious about your home’s electrical service, open the main breaker panel and look for the largest breaker switch in the panel, usually mounted at the top of the panel. The number on the switch will tell you the total amps of your home’s electric service.
Below the main breaker, electric service is divided up by smaller circuit breakers which govern the amount of electricity available to each circuit. Those circuits usually represent individual rooms, but may also represent hard-wired appliances like air-conditioners, furnaces, and water heaters. So, for example, of the 200 amps available to a home, the kitchen may have two 20 amp circuits, the bedroom may have a 15 amp circuit, the air-conditioner a 30 amp circuit, and so on. These circuit breakers work much the same as the main breaker – if an electrical overload occurs, the breaker automatically shuts off the electricity to the circuit, reducing the chance of fire.
Each circuit should be clearly labeled on the inside of the main breaker panel door (i.e. “living room” or “air-conditioner”). This will make it easy to know which breakers control which rooms or hard-wired appliances when you need to turn them off to replace a switch or outlet or perform maintenance on a hard-wired appliance.
Be aware that some older homes may still use fuses instead of breakers. Fuses are meant to be weak links in an electrical circuit which “burn out” safely when an overload occurs on a circuit before the circuit itself can overload and cause a fire. Once a fuse burns out, the overload must be fixed and the fuse then must be replaced by a new fuse with the same amp rating before the circuit will work again. Never replace a larger fuse with a smaller one. That’s because wires are rated in amperage also, so the fuse and wire size are determined by the load requirement of the electrical circuit. This older type of system is less safe than the newer, breaker-based systems.
From the smaller circuit breakers, bundles of wires run through walls, ceilings, and floors to each room and hard-wired appliance. Each bundle of wire has at least three wires within – two with plastic insulation and one bare. The black and/or red insulated wires are the “hot” wires coming directly off of the circuit breakers. The white insulated or “neutral” wire carries the current back to the electrical source at the panel. The bare copper wire is the ground wire, which is the safety part of the circuit. The two wires insulated wires are attached to outlets or switches so that when nothing is plugged in or a switch is in the off position, the wires do not meet. When you plug something into an outlet or turn a switch on, you complete the circuit, allowing electricity to flow through a light or appliance to activate it.
The ground wire is literally a direct path to the ground which acts with the circuit breaker, in the event of a short circuit. It is attached to all metal parts of a fixture or appliance. If a faulty appliance, frayed wire, or wet conditions give electricity a separate, less resistant path to the ground, the ground wire acts as a path of least resistance, allowing the excess electricity to travel directly to the ground and triggering the circuit breaker to shut off, helping avoid electrocution or fire.
While standard circuits to plugs and outlets are usually 110 volts, some larger hard-wired and plug-in appliances, like electric ovens, ranges, and clothes dryers, are 220 volt
Some circuits don’t travel to rooms, but to individual, hard-wired appliances. Most commonly these are appliances which require a lot of electricity like air-conditioners, electric furnaces, and electric water heaters. If labeled carefully, it is then easy to turn off power when replacing or servicing hard-wired appliances. Smoke alarms in modern homes are often hard-wired, and each will also have a battery back-up for additional safety in the event of a power outage. Mike Ashenfelter says, “Carbon Monoxide detectors are now also required in many jurisdictions. In new homes, or remodels smoke detectors must be hard-wired and battery backup. Combination CO and Smokes are available for installation. In some areas CO detectors can be of the plug in type, and do not have to be hard wired. Always check your local codes.”
The most common safety device beyond the breaker system is the Ground Fault Circuit Interrupt (GFCI) outlet or breaker. A GFCI senses the moment when a person begins to receive a shock, and shuts off the electricity at the outlet or breaker within milliseconds, avoiding the shock and potential electrocution. GFCIs are typically installed in locations where water may be present, like bathrooms, kitchens, unfinished basements, garages, and even outdoors. The most common type of GFCI is the outlet, but GFCI breakers can also be used in the main breaker panel to give all outlets in a given circuit GFCI protection.
GFCIs look like typical electrical outlets, but also include a test and a reset button. In the event that a GFCI is tripped, pressing the reset button will restore power (assuming the original problem is fixed). Since GFCIs include electronic sensors, and are subject to possible failure over time, homeowners should test them once a month to ensure that they are still working. Press the test button, which will trip the GFCI, then press the reset button to restore power. If pressing the test button doesn’t trip the GFCI, or pressing the reset button doesn’t restore power, the GFCI should be replaced.
A “ground fault” is an extreme event, when water or metal complete a circuit outside of the intended circuit. Direct metal-to-metal or water-to-metal electrical shorts are called “dead shorts,” and are easily detected by a GFCI device. However, when the fault in the circuit is less direct, it may not result in a dead short, but in electrical arcing, which a GFCI may not detect. In this case, as when a nail is driven into the wall and accidentally through an electric cable, the damage to the wires within can cause electricity to leap a very small gap, creating a white-hot “arc” between the not-quite-touching metal wires. Accidental arcing in an electrical circuit is just like intentional arcing with an arc-welder, with very hot temperatures resulting, sometimes exceeding 10,000ᵒF. These high temperatures can ignite wood framing, insulation, and other nearby combustibles, potentially resulting in a house fire. Arcing can occur in many situations, including at loose connections or where furniture impinges on electrical cords, and can often occur inside of walls.
The solution is to install Arc Fault Circuit Interrupts or AFCIs. Only AFCIs can prevent this type of hazard. AFCIs are now required by the National Electrical Code in many areas of the home including bedrooms, family rooms, dining rooms, living rooms, sunrooms, closets, hallways and similar rooms or areas. Like GFCIs, AFCIs can be of the outlet type or the circuit breaker type.
Installing a New System
Because of the potential, inherent risks involved in installing and servicing of electrical systems, they are subject to rigorous national and international regulations through building electrical codes. Ashenfelter says, “In most areas building permits are required and can be obtained from your local building department.” Systems should always be installed by trained professionals, adhering to the most current codes. System plans are subject to approval by city building codes offices. An electrical inspector will also inspect the system twice during installation: once after wiring, just before the walls are closed in, and once when the home is completely finished, after outlets, switches, lighting, and hard-wired appliances are installed.
That said, it’s important that you are involved in making decisions about your new electrical system. While things like minimum number of outlets and distance between them are stipulated by codes, there are still many decisions to make. Once installed, it’s difficult to change key elements of your system, so you will want to indicate things such as the number, type, and placement of outlets, light fixtures, switches, and hard-wired appliances. Many decisions will depend on how you intend to use each room, and where things like furniture, appliances, and electronics will be located. Once the walls are up for your new home, but before the wiring has begun, it’s okay to walk through the unfinished rooms with the electrician and change the plan. It’s often easier to visualize an electrical plan when walking through the unfinished rooms than on paper architectural drawings.
It’s also important to communicate any special electrical needs you may have. Here are a few things you may want to consider in your home’s electrical system design and communicate to your architect or electrical engineer who is helping to plan your system:
· A well-thought out lighting design is vital. Lighting affects not only the aesthetics and ambiance in a home, but also the safety and security of its occupants and the home’s overall energy efficiency. Be sure to create a lighting design that considers all of these aspects
· Will you have a home office or complicated home theater system in your new home? If so you may require an advanced wiring system to handle loads, potential surges, or power conditioning.
· Do you have family members who are children, elderly, disabled, or who have special needs? Electrical systems can be designed for enhanced safety and/or universal access.
· If you plan to use super-efficient LED lighting in your home, tell the electrician. Special dimmers are required for these types of bulbs.
· Energy use monitoring and automation can help a homeowner see their energy use and then automate parts of the system for maximum comfort, energy efficiency, and safety. Think about integrating both into your system during the design process.
· Include other wiring requests like telephone, data, cable and satellite TV, and security systems during the design process. Many times, this wiring can be brought into a central “hub” which then distributes each of the services throughout the house.