MaterialsFebruary 3, 2025• 10 min read

Aluminum vs Copper Wiring: Pros, Cons, and NEC Requirements

Both conductors have their place. Learn when to use each and how to avoid common aluminum wiring problems.

COPPERCuBetter conductivityHigher costALUMINUMAlLower costLighter weightVS

The Basics

Copper has been the gold standard for electrical wiring, but aluminum offers significant cost and weight advantages. Modern aluminum conductors and terminations have overcome many historical issues, making aluminum a viable choice for many applications.

Ampacity Comparison

Aluminum requires larger wire sizes to carry the same current as copper—typically about 2 AWG sizes larger:

Ampacity Comparison (75°C, NEC 310.16)Wire SizeCopperAluminumRatio#6 AWG65A50A77%#4 AWG85A65A76%#2 AWG115A90A78%#1/0 AWG150A120A80%#4/0 AWG230A180A78%250 kcmil255A205A80%500 kcmil380A310A82%

Copper Advantages

  • Higher conductivity: Smaller wire sizes for same ampacity
  • Better terminations: Works with all standard devices
  • Less expansion: Lower thermal expansion coefficient
  • More ductile: Bends without breaking
  • Preferred for branch circuits: Standard for 15-20A circuits

Aluminum Advantages

  • Lower cost: 60-70% less expensive than copper
  • Lighter weight: Half the weight of equivalent copper
  • Easier to pull: Significant labor savings on long runs
  • Abundant: More stable pricing than copper
  • Common for feeders: Standard for services and large feeders

Termination Requirements

The key to successful aluminum wiring is proper terminations. Check equipment labeling:

  • AL/CU: Rated for both aluminum and copper
  • CU only: Do NOT use with aluminum
  • AL-CU: Older marking, may have restrictions

Aluminum Termination Best Practices

  1. 1. Use only AL/CU rated devices and lugs
  2. 2. Apply antioxidant compound (if required by manufacturer)
  3. 3. Torque to manufacturer specifications
  4. 4. Re-torque after 24 hours when possible
  5. 5. Never mix aluminum and copper in the same lug (unless rated)

When to Use Each

Use Copper For:

  • • 15-20A branch circuits
  • • Device connections
  • • Flexible applications
  • • Short runs
  • • Where space is limited

Use Aluminum For:

  • • Service entrance conductors
  • • Main feeders
  • • Large branch circuits (≥#6)
  • • Long runs where weight matters
  • • Budget-conscious projects

Historical Issues with Aluminum

In the 1960s-70s, small-gauge aluminum wiring (#10 and #12) in residential branch circuits caused fire hazards due to:

  • Connections loosening from thermal expansion
  • Oxidation at connections increasing resistance
  • Incompatible devices not rated for aluminum

Modern solution: The NEC now requires proper rated devices, and larger aluminum conductors (for feeders) don't share these problems when installed correctly.

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