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All About Electrical Systems

A general overview of how electrical systems in the home have dramatically changed and advanced over the years.

Electrical Panel Nat Rea

It’s easy to take electricity for granted. We expect it to be available 24/7, and we depend on this amazing, invisible movement of electrons for innumerable everyday activities. Electricity’s importance is immediately evident whenever there’s a power outage, or when a malfunction causes a shock or a fire.

Old houses are particularly prone to electrical problems. For starters, they are almost always underpowered, relying on 60amp or 100amp service rather than the 200amp service that many newer houses use today. Other common problems include ungrounded circuits, wiring with deteriorated or missing insulation, and circuits controlled by old-fashioned fuses rather than modern circuit breakers.

The good news is that modern electrical components are designed, tested, and certified for safe, reliable, long-lasting performance. And building inspectors throughout the country rely on the same strict, detailed standards for electrical work in new construction and remodeling projects—provided by the National Electrical Code.

Understanding a few basic electrical terms is helpful when evaluating any kind of residential electrical work.

Basic Electrical Terms

Current is the flow of electricity through a conductor (electric wire, or any material where current can flow). The type of current supplied by your electric utility is alternating current (AC). But a small number of devices (like laptops, cordless phones, and low-voltage lights) require plug-in adapters that convert AC to direct current (DC).

Electricity can be measured in several ways. We use amperes (amp or amps) to measure current intensity (akin to the volume of water being pumped through a pipe.) A home’s electrical service is often described by the maximum amps of electricity that are available (200amps, for example). Voltage is a measure of electrical pressure—the power that’s “pumping” electricity through a conductor. If you multiply amps by volts, you get watts, a measure of the electrical power that is applied in a circuit.

SAFETY ALERT: Unlike other aspects of construction and remodeling, electrical work can pose life-threatening injuries when handling and installation errors occur. Severe shock, electrocution, and electrical fires can result. If you’re at all uncertain about wiring details, have a licensed electrician do your wiring work.

Electric Residential Wiring: Basic Elements & How They Work

A good way to gain an understanding of how electricity works in your house is to follow the path that current takes, beginning at the power lines that run along your street. In many houses, power lines enter the house through a service mast that extends up one side of the house. But this main power feed can also come through conduit (hollow pipe) buried underground. Before power lines enter the house, they pass through a meter box where the electric meter is installed to record your power use. From here, it’s on to the major elements described below.

Main service panel

This large metal box with a hinged cover is sometimes referred to as the breaker box or (in older houses with fuse-controlled circuits) the fuse box. Whatever name you use, this is the distribution center for all the electricity consumed in your house. There will be a main switch that can shut down (or turn on) all the power coming from the utility, along with individual switches (circuit breakers; see below) that control the power going to separate circuits.

Sub panel

Some houses need additional service panels (called sub panels) that distribute electricity to a group of circuits. A sub panel might be installed in a garage workshop, a pool house, or an outbuilding that contains lighting and electrical outlets.

Electrical cable

The electrical cable used for most residential applications today is often referred to as Romex cable. This form of non-metallic (NM) cable has a flexible plastic sheathing that covers several wires. Wire gauge and other information will be printed on the outer sheathing. The sheathing may also be color coded to further aid in identifying wire gauge and use.

Romex cable used in lighting circuits (white sheathing) will carry a designation of NM 14-2; this light-gauge cable is suitable for 15amp circuits. NM 12-2 cable (yellow sheathing) is used for receptacles and 20amp circuits. With either type of Romex, you can expect to find three wires inside the sheathing: a bare ground wire, a wire encased in white insulation, intended to serve as the neutral wire in the circuit, and a wire with black insulation that is usually the hot wire.

The electrical cable for large appliances (clothes dryers, electric stoves, heating and cooling systems) carries different designations that correspond to larger wire size, additional wires, and special uses, such as suitability for burial underground.

Older houses are almost certain to contain metal clad cable, commonly referred to as BX cable. BX is more difficult to work with than plastic-sheathed cable – especially when you need to pull wiring through holes in joists or studs. That’s why its use has diminished over the years. It can still be a good option when running electrical cable in exposed locations (against a basement wall, for example), where the use of plastic-sheathed cable is prohibited by code.


Electrical codes allow metal-clad “BX” cable to be used in some exposed locations. But it’s more common today to install hollow tubing (conduit) in these applications, and run electrical wire inside the tubing from one connection point to another. Electrical conduit can be made from steel or PVC plastic, and includes a wide range of fittings for connection to service panels and fixture boxes.

Circuit breakers

Your service panel will contain a series of switches that control different electrical loads used throughout the house. An average size house is likely to have at least several lighting circuits, several receptacle (aka outlet) circuits, plus circuits that control major appliances like the furnace, clothes dryer, water heater, etc.

All circuit breakers can be manually switched at the service panel, if you need to deactivate an electrical circuit that’s being worked on. But these devices are also designed to switch off (trip) automatically when a potential safety hazard is detected. Standard circuit breakers will trip in response to excessive current draw that can damage wiring and cause a fire hazard by overheating.

A circuit breaker designated as GFCI (Ground Fault Circuit Interrupter) will also trip automatically when current leakage is detected (a safety hazard that can occur when electric wires get wet). A breaker designated as an Arc Fault Circuit Interrupter (AFCI) will trip in response to overloading and sparks.

NOTE: Beginning in the 1960s, fuse boxes were phased out in favor of electrical systems controlled by circuit breakers. It’s important to replace an old fuse box with a circuit breaker system as soon as possible—not just for code compliance, but also for safety and convenience.

Residential Electric Code Requirements

Electrical code requirements stipulate where different types of breakers are used. For example, the receptacle circuits in bathrooms, kitchens, garages, basements, and other wet (or potentially wet) areas need GFCI protection. Building codes in many areas now require AFCI breakers for other household circuits, because their spark detection circuitry can protect against electrical fires.

Circuit breakers that feed receptacles will be rated at 15 or 20amps; this means they will automatically trip if current exceeds these ratings. Lighting circuits are controlled by 15amp breakers. Your service panel will also contain a limited number of larger “double-pole” breakers that have higher amp ratings for big appliances like stoves and clothes dryers.


Today, the incandescent light bulbs that we grew up with have largely been replaced by fluorescent and LED (light-emitting diode) lighting. It’s easy to understand why. Incandescent light fixtures can’t come close to matching the efficiency of fluorescent and LED lights. What’s more, incandescent light bulbs don’t last as long; they’ll burn out and require replacement while fluorescent or LED lights keep working. The benefits of saving money on your electrical bill and helping to save the environment through energy conservation are difficult to ignore.

Remodeling an old house is certain to involve lighting improvements. As you make these upgrades, the following tips may be helpful. Start by using LED lights wherever possible. When installing new recessed (aka can) lights in a ceiling beneath attic space, make sure to use fixtures with an IC (insulation contact) rating, so that attic insulation can be installed in direct contact with the fixture.

Also, air-seal around fixtures in the attic to help prevent the loss of warm air from your living space in wintertime. Include dimmer switches in your lighting plan. Being able to moderate the degree of light (especially in ceiling-mounted lights) is an easy and effective way to alter the ambience of living space.

Smoke and C0 alarms

New houses are required to have these safety devices installed, and old houses should have them, too. Both alarms are designed to sound loudly when smoke or carbon monoxide is detected. Every floor of a house should have a CO (carbon monoxide) detector.

Every bedroom should have a smoke alarm; it’s also recommended to have a smoke alarm outside a sleeping area. If you want to add this protection to your house, it might make sense to buy alarm units that combine both functions. And although these alarms can be hard-wired, most homeowners prefer to save time by installing battery-powered units. When the batteries lose their power, the unit will automatically beep, indicating that it’s time for new batteries.

Backup Power Supply

Power outages are a reality for many homeowners. In areas where long-term outages are likely to occur, many homeowners are installing backup power systems. The most common form of backup power is a home generator that can power devices directly, or through a transfer switch connection to your home’s main service panel.


The rule with generators is that more power costs more money. Small, portable generators (producing up to 2000 watts of electrical power; prices begin around $300) can power a refrigerator, laptop, phone charger, and household lights.

Larger mobile units ($1000 and up, rated up to 7,500 watts) can supply electricity directly to your service panel, through a transfer switch. These units can keep major hardwired devices (water pump, furnace, air conditioner) running and also power lights and appliances, as long as everything isn’t on at the same time.

The largest type of generator is a stationary unit (aka standby generator) that is installed on a platform outside the house. With prices that begin around $5,000, these generators are permanently wired to the main service panel, and include circuitry that will automatically turn on the generator when a power outage is detected.

SAFETY NOTE: Small generators typically run on gasoline. Larger models are usually powered by natural gas or propane. All models produce carbon monoxide and other hazardous emissions. Portable generators must never be used indoors, and all fuel should be stored in a safe, secure location.

Photovoltaic Systems

Harnessing solar energy to generate electricity is a great way to cut your utility costs while helping to save the planet. To further sweeten the deal, government incentives for renewable energy can help homeowners offset the cost of a PV system. To learn what incentives apply in your area, visit the Database of State Incentives for Renewable Energy.

If solar orientation is favorable, PV panels can be installed on the roof of a building, or on a ground array. The electricity generated by a PV system can be used in several ways. It can feed into your main service panel to provide household electricity. If your PV system is generating more power than you can consume, this excess electricity is supplied to your electric utility. In states with net metering laws, your electric utility must pay you for this excess power.

A final option is for your PV system to store solar electricity in a battery backup system. This enables you to use solar electricity after the sun goes down. By combining a PV system with battery backup, you can maintain electrical service when there’s a power outage—an alternative to backup power supplied by a generator.

Common Electrical Problems

Outdated systems

There are good reasons to make electrical upgrades a top priority when renovating an old house. Shock and fire hazards are possible with old wiring that has missing or deteriorated insulation. Two-prong receptacles pose a shock or electrocution hazard because they lack grounding protection. A fuse box won’t provide the same level of protection as modern circuit breakers.

Remodeling mistakes

When assessing any older home, it’s wise to look for jury-rigged electrical work done by an earlier owner. Many of these mistakes are obvious—like basement outlets that don’t have cover plates, or Romex cable that’s exposed on the wall. But there are other unsafe retrofits that only an experienced electrician or building inspector can identify. If you’re the new owner of an old house, it’s smart to hire a professional to thoroughly inspect your electrical system.

Overloaded circuits

Too many devices plugged into a single circuit can cause wiring to overheat, while also damaging the appliances on the circuit. Upgrading to a higher-amp service can sometimes solve this problem. In other cases, it may simply be necessary to add more circuits, and install some new receptacles.

Power surges

Your electrical system can occasionally get a high-voltage jolt from the electrical grid, caused by a lightning strike or a malfunction at the utility. To prevent this type of power surge from damaging electronic devices like computers and monitors, you can have a whole-house surge arrestor installed.