Electrical and Phone Wire

Start with the distinction that trips up most buyers. Wires are individual conductors; electrical cables bundle them together for added protection, organization, and easier installation. A length of Romex is technically a cable — two or three conductors plus a ground inside one jacket. THHN sold off the spool is wire — a single conductor. Knowing which you’re buying tells you half of what you need to know.

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The other half is matching the wire to the job. Selection depends on the load, the environment, and code requirements. Get the gauge wrong and you’ve built a fire hazard. Get the insulation wrong and the wire fails the first wet spring. And the rule that matters most for anyone running data or phone lines: power wiring and communications wiring are two different systems that never share a cable.

Matching Wire Type and Gauge to the Job

Power wire gets sized by American Wire Gauge. The counterintuitive part: AWG specifies wire size, and the greater the wire diameter, the smaller the number. A 14 AWG conductor is thinner than a 12. Smaller number, fatter wire, more current.

Here’s how the common residential sizes line up with circuits:

Wire Gauge	Circuit	Typical Use
14 AWG	15A	General lighting, receptacles
12 AWG	20A	Kitchen, bath, garage circuits
10 AWG	30A / 240V	Larger appliance loads
6 AWG	50A	Heavy 240V loads

Those gauge-to-amp pairings come straight from standard practice: 14 AWG for 15A circuits and 12 AWG for 20A circuits, and for 240V, 10 AWG at 30A or 6 AWG at 50A. One rule overrides all of it. Always match the wire gauge to your circuit breaker’s amperage and verify requirements with your local authority. The authority having jurisdiction has the final word, and in this network that includes the difference between Montana and Idaho code.

The common Romex and NM-B sizes show up in two-conductor and three-conductor configurations. Two-conductor (a hot, a neutral, plus ground) handles standard circuits. Three-conductor (adding a red traveler) runs three-way switches and 240V circuits that need two hots. The stock list runs 14-2 and 12-2 for everyday work, 14-3 and 12-3 for switch legs and split circuits, and 10-2 and 10-3 for the heavier stuff.

THHN is the other half of the power picture. THHN and THWN wires are staples for industrial and commercial work, offering heat and moisture resistance — the thermoplastic insulation handles high temperatures while the nylon coating protects against abrasion and chemicals. These are individual conductors pulled through conduit, sold by color so you can keep your hots, neutrals, and grounds straight on a run. The stock here covers 12 and 14 AWG in black, white, green, and red.

Copper or Aluminum

For house wiring, this isn’t much of a debate. Copper remains the industry standard for its reliable conductivity and durability, minimizing energy loss where efficiency matters. It terminates clean and holds up.

Aluminum has its place on the big runs. Aluminum offers a cost-effective alternative, particularly for large-scale installations where its lightweight nature eases handling and reduces structural strain. The trade-off: aluminum requires larger gauges and specific antioxidant precautions at terminations. Skip the antioxidant compound at the connections and you invite trouble down the line.

Matching Insulation to Montana Conditions

Same gauge, wrong jacket, dead wire. The environment drives the type more than anything.

NM-B — plain Romex — is an indoor product, full stop. Nonmetallic cable is the go-to for home electrical systems, with a protective plastic sheath that safeguards the conductors and provides insulation, useful for connecting outlets, switches, and lighting fixtures. But there’s a hard limit. Due to its lack of moisture resistance, it’s limited to dry, interior locations.

The moment you head outdoors or into the ground, you switch to UF-B. Unlike NM cable, the solid plastic sheath of UF cable provides a watertight seal that prevents moisture from penetrating and damaging the conductors, making it suitable for direct burial without additional protection. This is the wire for the job that comes up constantly on rural Montana properties: UF cable powers outdoor lighting, irrigation systems, or detached structures like garages or sheds. A run out to the shop or the detached garage, buried through ground that goes from frozen to saturated every spring — that’s UF-B territory, not Romex. The stock list carries 12-2 UF in the gray jacket.

THWN handles wet locations a different way. THWN wires are designed for wet environments, and when housed in conduit they’re suitable for outdoor installations, ideal for exposed runs or use within conduit systems in areas like basements, garages, or industrial facilities.

When the run needs mechanical protection, armored cable earns its keep. Shielded and armored constructions protect the conductors where physical damage is a risk. The aluminum MC stocked here comes in 12-2 and 14-2.

One more for cold-weather work: cold-flex cord. The SJEOW-type rubber jacketed cords stay pliable when the temperature drops, which matters when you’re dragging an extension run across a jobsite in January instead of fighting a cord that’s gone stiff as rebar.

Keep Power and Communications Wiring Apart

This is where DIYers get into real danger. Phone and data cable is a different animal entirely. Telephone wires are low-voltage cables, typically carrying around 48 volts of direct current when idle. And they’re thin. Telephone cable uses extremely thin wires, often 24 or 26-gauge, meant only for transmitting data and voice signals. Compare that to power wiring: electrical wiring like Romex uses thick copper conductors, usually 12 or 14-gauge, designed to carry heavy electrical loads safely.

So no, you can’t repurpose an old phone jack into a 120V outlet. You cannot directly convert a phone jack to a standard 120-volt electrical outlet — attempting to do so is incredibly dangerous and poses a significant risk of fire and electrocution. The physics are unforgiving. Sending 120 volts through thin telephone wire would instantly overheat it, melting the insulation and creating a severe fire hazard.

On the data side, the common twisted-pair grades break down simply. Cat5e is twisted pair cable for Ethernet networks — four pairs of twisted copper wires capable of carrying data up to 1 gigabit per second. Step up and Cat6 is similar to Cat5e but capable of carrying data up to 10 gigabits per second, commonly used in high-speed network applications. The twist is the whole trick — low-voltage phone or data cables like Cat5e/6 use twisted pairs to minimize interference. For TV and satellite, coax still does the work: coaxial cable is a reliable choice for television, cable internet, and satellite connections.

Code keeps these systems physically separated for good reason. Communications wiring must be separated from electric light, power, Class 1, and nonpower-limited fire alarm conductors, and where practicable, maintain a separation of not less than 6 feet between communications wiring and lightning protection conductors. That lightning rule isn’t academic during Montana storm season. The grounding side reinforces it: locate the primary protector as close as practicable to the point of entrance, keeping the shortest practicable distance to the grounding conductor — very important during lightning events. And don’t tie your incoming data line to the power mast: don’t attach incoming communications cables to the service-entrance power mast.

If you’re running a network, run the right cable for it. Mixing phone and LAN on one cable is a headache that limits you later. 1000base-T gigabit Ethernet uses all 4 pairs (8 conductors) and cannot be used with mixed LAN and telephony wiring. The smart move is to pull a separate run. Pull two separate wires — one to carry telephony and one to carry LAN, both cat 5e or 6 — to a single multi-use jack. This will save a lot of hassle.

The grounding conductors that tie these systems to earth have their own spec. The grounding conductor must be copper or other corrosion-resistant conductive material, not smaller than 14 AWG, as short as practicable, and run in as straight a line as practicable. The stock list carries solid copper ground in 6 AWG and 4 AWG.

Frequently Asked Questions

What’s the difference between a wire and a cable? A wire is a single conductor. A cable bundles multiple conductors inside one protective jacket. Electrical cables bundle wires together for added protection, organization, and easier installation. THHN off a spool is wire; Romex with its two or three conductors and ground is a cable.

Can I use indoor Romex for a run out to my shed or detached garage? No. NM-B Romex is built for dry interior spaces only. Due to its lack of moisture resistance, it’s limited to dry, interior locations. For an outdoor or buried run to an outbuilding, use UF-B, which has a watertight sheath suitable for direct burial without additional protection and powers detached structures like garages or sheds.

Why is a smaller AWG number a bigger wire? That’s just how the gauge system works. American wire gauge specifies wire size, and the greater the wire diameter, the smaller the value. So 12 AWG is physically thicker and carries more current than 14 AWG.

Which gauge goes with which breaker? For standard residential circuits, 14 AWG pairs with a 15A circuit and 12 AWG with a 20A circuit; for 240V, use 10 AWG at 30A or 6 AWG at 50A. But never guess. Always match the wire gauge to your circuit breaker’s amperage and verify requirements with your local authority.

Can I turn an old phone jack into a power outlet? No. You cannot directly convert a phone jack to a standard 120-volt electrical outlet; attempting to do so is incredibly dangerous and poses a significant risk of fire and electrocution. Phone wire is far too thin — sending 120 volts through thin telephone wire would instantly overheat it, melting the insulation and creating a severe fire hazard. The location can be reused to run new, properly sized electrical cable, but the phone wire itself can’t carry power.

Should I run one cable for both phone and internet? Better to run separate cables. 1000base-T gigabit Ethernet uses all 4 pairs and cannot be used with mixed LAN and telephony wiring. Pulling a dedicated Cat5e or Cat6 line for data and a separate line for phone keeps your options open and saves grief down the road.

Copper or aluminum for house wiring? Copper for residential work. Copper wire remains the industry standard for its reliable conductivity and durability. Aluminum is mainly a large-scale play and requires larger gauges and specific antioxidant precautions at terminations.