NEC 110.5: Conductors - Or "What the Hell Are These Wires Made Of?"

The Plain-English Breakdown

Listen up, because this is one of those sections that seems stupidly simple until you're standing in front of an inspector explaining why you used solid gold wire because "the customer wanted the best."

Here's the deal: When you're pulling wire to carry current (you know, doing actual electrical work), you've got THREE legal options, and that's it:

Copper - The gold standard (ironically)
Aluminum - The lightweight budget option that everyone side-eyes
Copper-clad aluminum - The mullet of conductors (copper party on the outside, aluminum business on the inside)

That's your menu, folks. Unless the Code specifically says "hey, you can use something weird here," you're picking from these three.

Now here's the kicker: Whenever the Code gives you a wire size (like "use 12 AWG for this"), they're talking about COPPER unless they specifically say otherwise. Copper is the default, the baseline, the vanilla ice cream of conductors. If you decide to go rogue and use aluminum or copper-clad aluminum, YOU gotta do the math and upsize accordingly. The Code ain't holding your hand on that conversion.

Think of it like this: The Code is written by copper guys, for copper guys, assuming you're using copper. Aluminum? That's on you to figure out, chief.

Key Takeaways (The Stuff That Actually Matters)

🔧 Only THREE conductor materials are legal for current-carrying conductors:

Copper
Aluminum
Copper-clad aluminum

🔧 All Code wire sizes default to COPPER unless specifically stated otherwise

🔧 If you use aluminum or copper-clad aluminum, YOU must upsize - typically going up 1-2 sizes (like 12 AWG copper becomes 10 AWG aluminum)

🔧 "Unless otherwise provided in this Code" - This is your escape hatch for special cases like grounding electrode conductors, but don't get cute with it

🔧 This applies to CURRENT-CARRYING conductors - we're talking hot wires and neutrals that actually do work

Real-World Jobsite Scenarios

SCENARIO 1: The "Aluminum Special" Disaster

You're roughing in a house, and your supplier "accidentally" delivers aluminum wire for your branch circuits instead of copper. The apprentice asks if it's cool to just use it since "wire is wire, right?"

WRONG. That 12 AWG aluminum isn't equivalent to 12 AWG copper. You need 10 AWG aluminum to handle what 12 AWG copper does. Plus, now you're dealing with anti-oxidant paste, special terminations rated for aluminum (CO/ALR), and torque requirements that'll make your wrist hurt.

Send it back. Trust me, the $200 you "save" will cost you $2,000 in callbacks when connections start failing.

SCENARIO 2: The Inspector's Favorite Gotcha

Inspector walks up to your panel and sees 10 AWG going to a 30-amp breaker. "Show me your calculations," he says with that smirk they all have.

You proudly show him your work... except you used the copper ampacity table for your aluminum wire. Whoops. That 10 AWG aluminum is only good for 25 amps (with 75°C terminations), not the 30 amps you thought. Now you're either upsizing to 8 AWG aluminum or re-pulling in copper.

SCENARIO 3: The "But My Buddy Said..." Story

Buddy from another state tells you he saved a fortune using aluminum for a service entrance. You figure "why not?" and spec aluminum service entrance conductors for your next job. You look at Table 310.16, see that 2 AWG aluminum is good for 90 amps at 75°C, and you're golden, right?

Actually, yeah! This is one place where aluminum makes total sense. Service entrances, feeder runs, bigger wire sizes - aluminum is legit here. You'll upsize compared to copper, but the weight savings and cost difference actually matter on a 200-foot run of 4/0.

Just don't forget: Those terminations MUST be rated for aluminum (look for "AL" or "CU/AL" on the lug), and you better use that anti-ox compound like your license depends on it (because it does).

What to Study (For The Exam Nerds)

HIGH PROBABILITY TEST MATERIAL:

Know your three legal conductor materials - They love asking "which of the following is NOT an acceptable conductor material" questions
Understand that Code tables assume COPPER - Expect questions like: "If the Code specifies 10 AWG for a circuit, what size aluminum conductor is required?" (Answer: You gotta look it up in the ampacity tables - probably 8 AWG)
Memorize the ampacity difference - Aluminum is typically rated about 80% of equivalent copper. A 12 AWG copper (20A) needs 10 AWG aluminum to hit that same 20A rating
Know the exceptions - Grounding electrode conductors can be copper, aluminum, or copper-clad aluminum (110.5 covers this), but they can also be other materials in specific applications
Special terminations for aluminum - While not directly in 110.5, know that using aluminum triggers a bunch of other requirements (110.14, anti-oxidant compound, CO/ALR devices, etc.)

EXAM TIP: They LOVE giving you a calculation problem using aluminum conductors where they expect you to know that the Code tables default to copper. Don't fall for it!

The Bottom Line

This section is basically the Code saying: "We trust you with three materials. Copper, aluminum, or copper-wrapped aluminum. That's it. Don't get creative. Don't use steel. Don't use brass. Don't use your nephew's 'revolutionary new conductor material.' And if you're not using copper, you better know what you're doing because we wrote this whole book assuming you are."

It's boring. It's basic. But mess it up, and you'll either fail inspection or - worse - create a fire hazard when those undersized aluminum conductors start cooking.

Remember: Copper is king, aluminum is legal but picky, and copper-clad is trying to be both. Pick your fighter and size accordingly.

Now get back to work! 🔌⚡