Common Types of Electrical Wiring Used in Homes

Knowing the basic types of wires is essential for almost any electrical project in a home. When you’re installing new wiring, choosing the right wire or cable is half the battle.

And when you’re examining the existing wiring in your home, the type of wiring can tell you a lot about the circuit the wiring belongs to – for example, when you open a junction box and need to determine which wires are in the installation and where they go.

Types of Electrical Wiring

What is An Electric Cable?

Wiring for modern homes is relatively standard, and most homes built after the mid-1960s have similar wiring types in the U.S. and other countries that use the NEC. Any new electrical installation requires new wiring that complies with local building codes.

An electrical wire is a type of conductor made of a material that conducts electricity. In household wiring, the conductor is usually copper or aluminum and a solid wire or cable. Most home wiring is insulated, which means it is wrapped in a non-conductive plastic jacket. One notable exception is ground wires, which are generally solid copper and are either insulated with green insulation or are uninsulated (uninsulated).

The most common type of wiring in modern homes is non-metallic (N.M.) wire, which consists of two or more individual wires wrapped in a protective plastic jacket. The NM cable usually contains one or more “hot” (current-carrying) wires, a neutral wire, and a ground wire.

As an alternative to the N.M. cable, individual cables can be installed inside a rigid or flexible metal or plastic tube called a conduit (pipe). Conduit (pipe) is typically used where the wiring will be exposed and not hidden within walls, floors or ceilings.

Common Types of Electrical Wiring Used in Homes

1. N.M. cable (Non-metallic cable)

non metallic cable (NM)
non metallic cable (NM)

Commonly called “Romex,” after a famous brand name, the N.M. cable is designed for indoor use in dry locations. Almost all wiring in a modern home is N.M. cable. The most common sizes and their amperage ratings are:

  • 14 gauge (15 amp circuits)
  • 12 gauge (20 amp circuits)
  • 10 Gauge (30 amp circuits)
  • 8 gauge (40 amp circuits)
  • 6 gauge (55 amp circuits)

The electrical wiring system in most homes is created with non-metallic (N.M.) wire. Commonly called Romex, this wire has 2-3 conductors and a bare ground wire and is plastic coated.

N.M. is excellent because it is quick and easy to install, but it is also relatively inexpensive. It is available in various sizes and is color-coded by gauge for the convenience of the electrician. You can also see NM-B, where the B represents a heat rating of 194 degrees Fahrenheit, which means the wire can operate at high levels without overheating, melting, or causing a fire.

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2. Underground Feeder Cable

Underground feeder cable

Subway feeder cable (U.F.) is a non-metallic cable designed for wet locations and direct burial in the ground.

It is commonly used for outdoor power equipment such as streetlights and outdoor lighting.

Like standard N.M. cable, U.F. contains hot (phase) and neutral insulated wires, plus a bare ground wire. But while the sheath on the N.M. cable is a separate plastic sheath, the U.F. sheath is a solid plastic that surrounds each cable.

3. THHN / THWN Cable:

THHN and THWN cable

THHN and THWN are codes for the two most common types of insulated wire used inside a conduit or duct.

Conduit or duct is often used in unfinished areas, such as basements and garages, and for short exposed runs inside the home, such as wiring connections for garbage disposals and water heaters.

The letters indicate specific properties of the cable insulation:

  • T: thermoplastic
  • H: heat resistant; H.H. means highly heat resistant
  • W: classified for wet locations
  • N: nylon coated, for greater protection

4. Low Voltage Cables

Low voltage cables

Low voltage wiring is used for circuits that generally require 50 volts or less. Three common types are ornamental lighting wire, bell wire (for bells), and thermostat wire.

The size of the wires varies from approximately 22 to 12. Low-voltage wires are usually insulated and may be contained in the cable jacket or combined in pairs, similar to lamp wire. It should be used only for low voltage applications.

5. Telephone and Data Cable

Telephone and data cable

Telephone and data cables are low-voltage cables used for “landline” phones and Internet connections.

The telephone cable may contain four or eight wires. Category 5 or Cat 5 cable, the most common home data cabling type, has eight wires wound in four pairs.

It can be used for both data and telephone transmission and offers higher capacity and quality than standard telephone cable.

Understanding the Sizes and Installation of Standard Wiring in a House

Much of what you need to know for electrical repairs and remodeling is about understanding the characteristics of the wiring: how to identify it, how to buy it, and how to install it with the proper connections.

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If you plan an electrical project, learning the basics of wiring and installation is the best way to start.

Understanding basic wiring terminology and identifying the most common types of wires and cables will help you research wiring problems and choose wiring for new remodeling installation projects.

Understanding Cable Size

Correct cable size is critical to any electrical cable installation. Cable size indicates the metal conductor’s diameter in the cable and is based on the American Wire Gauge (AWG) system.

The gauge of a cable is related to the current-carrying capacity, or the amount of amperage the cable can safely handle. When choosing the right size wire, you should consider the gauge, the capacity (amperage), and what it will be used for.

Wires that do not correctly match the amperage of the circuits they serve can create a significant risk of short circuit and fire.

Color Coding of Electrical Cables

Color coding is used on both the outer sheathing of grouped electrical cables and the individual wires within internal cables or conduits. Understanding this color coding can help you identify what the wiring is used for and maintain consistency within an electrical system.

Wire coloring relates to the wires’ size within the wire and the amperage rating of the wire. For example, the white-jacketed N.M. wire is used for 15-amp circuits, while the yellow N.M. wire is rated for 20-amp circuits.

The coloring on individual conductor wires generally does not indicate a size or rating but the standard or preferred use of the wire. For example, black and red cables usually are used for power or “hot” connections, and white wires are generally “neutral” conductors connected to the ground. Cables with green insulation and bare copper wires are used for grounding wires.

Understanding Electrical Wiring Labeling

Electrical wires and cables have stamped or printed markings on their insulation or outer jacket. These markings provide essential information about the wiring and insulation, including the wire’s size and material, the type of insulation, the amount of wire contained (within a wire), and any ratings or unique characteristics of the wire.

While observing the color of the wire will help you narrow down the store’s choices, reading and understanding the labels on the wire is the best way to ensure you get the right graded material for your project.

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Direct Burial Cable

The standard electrical cable is designed to operate indoors, where it remains dry and is protected by a wall, ceiling, or floor structures.

For outdoor projects or when running the subway, you should use a direct burial cable, which can be installed subway with or without conduit (depending on local building code standards).

With direct burial cable, the individual conductor wires are embedded in solid vinyl to protect them entirely from moisture.

How to Strip Electrical Cables

Stripping an electrical cable involves removing the plastic insulation surrounding the metal core of the cable. It is essential to do this carefully so that the metal is not damaged.

The procedure is simple but requires a unique wire stripping tool and an understanding of how to use it. This is a critical skill and a tool for do-it-yourselfers to have for any wiring project.

The Maximum Number of Wires Allowed in the Conduit

When running individual electrical cables in conduit, there is a limit to the number of cables allowed.

The maximum permitted number is known as the “full capacity,” which depends on several factors, including the size of the conduit, the caliber of the cables, and the conduit’s material. Metal (EMT), plastic (PVC), and flexible conduit have different filling capacities, even when they are nominally the same size.

Wiring of an Electrical Circuit Breaker Panel

The electrical panel, or service panel, is the power distribution point for a home electrical system. This is where all the individual circuits in the house get their power and protected by switches or fuses.

Wiring an electrical panel is a job for a licensed electrician. Still, do-it-yourself experts should have a basic understanding of how a panel works and the critical role that switches play in any system.

Basic wiring concepts: electrical disconnect switches

An electrical disconnect provides a means of disconnecting power to a home’s electrical system from an outdoor location. It is usually mounted under the electric meter, either on the side of a house or on the utility pole. Not all homes have a dedicated disconnect.

They are commonly used when the service panel (which also serves as the main disconnect) is located indoors and, therefore, not accessible to emergency services or utility workers. Like electrical service panels, a disconnect must be installed by a licensed electrician.