Understanding the Main Types of Electric Wire for Home and Workshop Wiring

Types of electric wire refers to the specific combination of conductor material, insulation chemistry, and outer jacketing that dictates where a cable can safely carry current. When you select a wire type for a project, you are not just choosing a color or a physical shape; you are defining the circuit's maximum thermal limit, its resistance to moisture, and its physical vulnerability to crush damage. Choosing the wrong type can lead to insulation breakdown, short circuits, or a failed inspection, even if the copper gauge itself is technically thick enough to handle the amperage.

The Core Types of Electric Wire for Residential and Workshop Use

Before pulling any wire through a stud bay or conduit, you need to know the baseline specifications of the cable in your hand. The National Electrical Code (NEC) categorizes these primarily by their insulation letter designations and jacket configurations. Below is a spec-sheet-table of the four most common types of electric wire you will encounter in residential and light commercial work, based on standard 12 AWG copper pricing and ratings.

Note: Pricing reflects average 2026 retail costs from major suppliers like Southwire and Cerro Wire; bulk contractor pricing will be lower.

What Insulation and Jacket Types Change in a Real Circuit

The insulation type fundamentally changes the ampacity column you are legally allowed to use when sizing your breaker, and it dictates the physical routing methods available to you. This is where many DIYers make critical errors.

Take NM-B cable, universally known by the brand name Romex. The individual conductors inside a modern NM-B jacket are actually rated for 90°C. However, per NEC Article 334.80, the ampacity of NM-B cable must be determined using the 60°C column of NEC Table 310.16, regardless of the 90°C insulation. Why? Because the overall PVC jacket and the enclosed nature of a stud bay trap heat, and older legacy devices (like standard 15A/20A receptacles) often have termination lugs only rated for 60°C. Therefore, a 12 AWG NM-B wire is strictly limited to 20 Amps, even though 12 AWG copper in the 90°C column can theoretically handle 30 Amps.

Conversely, if you pull individual 12 AWG THHN wires through a metal EMT conduit, the heat dissipation is vastly superior. You can use the 90°C column for derating calculations when bundling multiple circuits in that conduit, though your final breaker size is still limited by the lowest-rated termination point in the circuit (usually the 75°C lugs on a modern breaker). Furthermore, the nylon coating on THHN makes it highly slick and resistant to chemical degradation, allowing it to survive the friction of being pulled through 100 feet of conduit with junction boxes—a feat that would strip the soft PVC jacket right off an NM-B cable.

Where You Meet This in Practice: A Worked Numeric Example

Let's look at a real-world scenario where wire type and sizing intersect: running a 120V, 20-Amp branch circuit from your main panel to a detached workshop outlet, a distance of 75 feet. You plan to run a heavy 1800W compressor and a 1200W space heater simultaneously, pulling close to the full 20A continuous load.

If you use standard 12 AWG NM-B buried inside the wall, you must calculate voltage drop to ensure your tools don't brown out. Using the standard voltage drop formula for single-phase circuits:

Plugging in the numbers: Vd = (2 × 12.9 × 20 × 75) / 6530 = 5.92 Volts.

A 5.92V drop on a 120V circuit is a 4.93% voltage drop. The NEC recommends keeping branch circuit voltage drop under 3% for optimal efficiency. At nearly 5%, your compressor motor will run hot, draw more current to compensate, and potentially trip the breaker or degrade its internal windings over time.

The Fix: Because you are running this through a conduit underground to the detached workshop, NM-B is illegal to use anyway (it is not rated for wet locations or direct burial). You must use THWN-2 conductors pulled through PVC conduit. To solve the voltage drop issue, you bump the wire size up to 10 AWG THWN-2 (CM = 10,380).

Recalculating with 10 AWG: Vd = (2 × 12.9 × 20 × 75) / 10380 = 3.72 Volts. This yields a 3.1% drop, which is vastly safer for motor loads and perfectly compliant with standard installation practices. For a direct-burial trench without conduit, you would substitute the THWN-2 for 10 AWG UF-B, accepting the higher material cost for the convenience of ditching without laying pipe.

Common Confusions: Gauge vs. Type and Solid vs. Stranded

When discussing the types of electric wire, beginners frequently confuse wire gauge (AWG) with wire type (insulation/jacket). AWG strictly defines the physical cross-sectional area of the copper. A 12 AWG wire has the exact same amount of copper whether it is wrapped in THHN, NM-B, or high-temperature silicone. The type defines what that copper is wrapped in, which dictates where it can be installed and how much heat the insulation can survive before melting or off-gassing toxic fumes.

A second major point of confusion is solid vs. stranded conductors. Many hobbyists assume stranded wire can carry more current because it has more surface area (due to the skin effect). At standard 60Hz AC mains frequencies, the skin effect is negligible for wire sizes under 1/0 AWG. The NEC treats solid and stranded 12 AWG copper identically for ampacity purposes.

However, they behave very differently at the termination point. Solid wire is rigid, easy to strip, and wraps cleanly under standard residential receptacle screw terminals. Stranded wire is flexible and ideal for pulling through conduit with multiple bends, but it tends to "mushroom" and fray when clamped under a standard screw lug. If you terminate stranded wire under a standard receptacle screw without using a crimped ferrule or a pressure plate, individual copper strands can escape the lug, reducing the contact area, increasing resistance, and creating a localized hot spot that can melt the device. Always use a calibrated torque screwdriver (like a Klein Tools 0-60 in-lb model) set to the manufacturer's specified inch-pound rating to ensure a safe termination, regardless of stranding.