Buying electrical cable can feel confusing once you see the aisle lined with dozens of similar-looking rolls. The good news is that the decision comes down to three questions: what type of cable do I need, what size should the conductors be, and what will the cable be used for? Answer those, and the choice becomes much simpler.
This guide explains how electrical cables are put together, the most common types and where each is used, how to read cable sizes and ampacity ratings, and what to check before you buy. It covers standard household and light commercial wiring as well as low-voltage and data cables.
What Is an Electrical Cable?
An electrical cable is one or more conductors bundled together, covered with insulation, and usually protected by an outer jacket. The conductor carries the current; the insulation and jacket keep that current where it belongs and protect the metal from moisture, heat, and abrasion.
People often use “wire” and “cable” interchangeably, but they are not the same thing. A wire is a single conductor. A cable is a group of two or more wires — or a single large conductor with heavy covering — assembled into one unit. When you strip the outer jacket off a cable, you find the individual wires inside.
The Basic Parts of a Cable
- Conductor: The metal that carries current, usually copper or aluminum. Copper conducts well and is the standard for most residential work. Aluminum is lighter and cheaper but requires larger sizes for the same job.
- Insulation: The colored layer wrapped directly around each conductor. Colors identify the function of each wire, such as hot, neutral, or ground.
- Jacket or sheath: The outer covering that holds the conductors together and adds physical protection.
- Shielding: A metal foil or braid found in some cables, used to block electrical interference in signal and data cables.
- Fillers and binders: Non-conductive material that keeps the cable round and holds its shape.
Common Types of Electrical Cable
Non-Metallic Sheathed Cable
This is the flat, plastic-jacketed cable found in most homes. It contains two or three insulated conductors plus a bare ground wire. It is meant for dry, protected locations such as inside walls, ceilings, and attics, and it is commonly used for lighting circuits, outlets, and appliances.
Armored and Metal-Clad Cable
These cables have a flexible metal covering over the conductors. That metal layer provides extra physical protection, so this type is often used in exposed areas, garages, workshops, and some commercial spaces where standard plastic-jacketed cable could be damaged.
Underground Feeder Cable
Designed for direct burial or wet locations, this cable has a solid, moisture-resistant jacket. It is used for outdoor lighting, detached buildings, and other runs that travel through soil or damp areas. Standard indoor cable should never be buried.
Service Entrance Cable
Heavier cable used to bring power from the utility connection into a building’s main panel. It is rated for higher current and is normally installed only by a qualified electrician.
Flexible Cords and Portable Cable
Stranded, flexible cables made for items that move or vibrate, such as lamps, tools, and appliances. The fine strands let the cable bend repeatedly without breaking. These are not meant to be run permanently inside walls.
Low-Voltage Cable
Used for doorbells, thermostats, landscape lighting, and control systems. The conductors are thin because the current is low, and the jacket is often rated for outdoor or burial use.
Data and Communication Cable
Cables that carry signals rather than power, including twisted-pair network cable, coaxial cable for television and internet service, and speaker cable. These rely on precise conductor spacing and shielding to keep signals clean.
How Cable Sizes Work
In North America, conductor size is given in AWG (American Wire Gauge). The numbering works in reverse from what you might expect: the smaller the number, the larger the conductor and the more current it can carry. A 12-gauge wire is thicker than a 14-gauge wire.
In many other countries, cable size is listed in square millimeters (mm²), which directly describes the cross-sectional area of the conductor. Larger numbers mean larger conductors.
Common sizes and their typical uses:
| Size (AWG) | Typical Use |
|---|---|
| 14 | Lighting circuits and low-demand outlets |
| 12 | General-purpose household outlets |
| 10 | Water heaters, dryers, and other heavy appliances |
| 8 | Ranges, subpanels, and large equipment |
| 6 | Main appliance feeds and short service runs |
| 2 and larger | Service entrances and main feeders |
Always match the cable size to the circuit breaker or fuse protecting it. Undersized cable overheats; oversized cable wastes money and can be difficult to terminate.
Voltage Ratings and Ampacity
Every cable carries two important ratings. The voltage rating tells you the highest voltage the insulation can safely handle. The ampacity is the maximum current the conductor can carry continuously without overheating.
Ampacity is not fixed. It depends on the conductor material, the insulation’s temperature rating, how many current-carrying conductors sit in the same cable, and how the cable is installed. Cable packed in insulation or run through a hot attic carries less current than the same cable in open air. This is why the same gauge can have different allowable currents in different situations.
Insulation and Jacket Materials
- PVC (polyvinyl chloride): The most common jacket material. Durable, affordable, and suited to general indoor use.
- Thermoset and cross-linked materials: Handle higher temperatures and are often used for heavier-duty or industrial cables.
- Rubber and flexible compounds: Used where cable must bend and flex constantly.
- Sunlight- and moisture-resistant jackets: Required for outdoor, wet, or buried installations.
How to Choose the Right Cable
- Identify the application. Decide whether the cable carries power, low-voltage control, or data signals.
- Check the environment. Indoors, outdoors, buried, wet, hot, or exposed? Each condition calls for a different jacket and rating.
- Calculate the load. Add up the current the circuit will draw, then choose a size with enough ampacity.
- Match the breaker. The protecting breaker or fuse must be sized for the cable, not the other way around.
- Confirm the conductor count. Most power circuits need a hot, a neutral, and a ground; some need an extra hot for multi-wire setups.
- Verify the labeling. The jacket printing states the size, voltage rating, temperature rating, and approved uses. Read it before buying.
Safety Points to Keep in Mind
- Never substitute a smaller gauge than the circuit requires.
- Do not use indoor-rated cable outdoors or underground, even temporarily.
- Look for recognized safety certification marks on the packaging.
- Follow local electrical codes. Rules on burial depth, protection plates, and cable types vary by area.
- Have major work — panels, service entrances, new circuits — installed and inspected by a licensed electrician.
Buying Tips: Length, Packaging, and Certification
Cable is sold by the foot, meter, or in pre-cut coils and boxes. Measure your run carefully, including the extra length needed for turns, entering boxes, and making connections. Buying slightly more than you need is usually cheaper than a second trip.
Check that the packaging lists the gauge or mm², the number of conductors, the voltage and temperature ratings, and the approved environments. Inspect the jacket for cracks, nicks, or kinks before installation, and store unused cable in a dry place away from sunlight.
Conclusion
Choosing electrical cable is really a process of elimination: pick the type that suits the environment, the size that matches the load and the breaker, and the jacket material that fits the conditions. Confirm the ratings printed on the jacket, buy a little extra length, and follow local codes. With those steps, you can walk into any supplier knowing exactly which roll you need.
If you found this helpful, explore our other practical guides on home wiring basics, circuit breaker sizing, and safe do-it-yourself electrical projects.