For a typical 100 amp residential service using aluminum conductors, the commonly recommended size is 1/0 AWG aluminum for the main feeders.

Quick Scoop: Short Answer

  • For most 100 amp services (main panel or subpanel): 1/0 AWG aluminum is standard best practice.
  • Some references list 3 AWG or 2 AWG aluminum as minimums by raw ampacity math, but many pros and guides still recommend going up to 1/0 for safety margin, voltage drop, and code-compliance across more real‑world situations.
  • Always confirm with your local electrical code and inspector , and have a licensed electrician size and install the conductors.

Why 1/0 Aluminum Is Usually Chosen

Even though aluminum can technically hit 100 amps at smaller gauges in tables, several real‑world factors push people toward 1/0 AWG:

  • Voltage drop : Longer runs (for example, to a detached garage or shop) can need a larger wire to keep voltage drop under about 3%.
  • Temperature and installation : Conduit fill, ambient heat, and insulation type all affect ampacity; going larger gives more headroom.
  • “Best practice” vs. minimum : Many electricians and industry guides treat 1/0 aluminum as the practical standard for 100 amp feeders, not just the bare minimum.

One guide aimed at homeowners notes 2 AWG, 1 AWG, and 1/0 AWG as common aluminum choices for 100 amp service, but calls 1/0 AWG the best practice size. Another detailed explainer on aluminum for 100 amp service repeatedly recommends 1/0 AWG aluminum under typical residential conditions.

Mini Section: Distance Matters

If you’re asking “what size aluminum wire for 100 amp service” because you’re feeding a subpanel some distance away , the run length changes the answer a bit.

  • Short runs (panel very close to meter):
    • Some references show 3 AWG aluminum as a theoretical minimum for 100 amps under ideal conditions.
* However, most homeowners and contractors still choose **1/0** so the same wire works for more situations and inspections.
  • Longer runs (around or over 100 ft):
    • Recommendations often increase the size (for example 1/0, sometimes even 2/0 for especially long or hot runs) to keep voltage drop in check.

Think of it like using a bigger hose the farther you’re trying to push water: more distance = more resistance, so you bump the size up.

Practical Tips & Safety

Always treat service wiring as a permit‑and‑inspection job, not a casual DIY chore.

  • Confirm with NEC and local code : Online tables are generic; local amendments or utility requirements can demand specific conductor types and sizes.
  • Use aluminum‑rated terminations : Lugs, breakers, and panels must be rated for aluminum conductors and torqued to spec.
  • Consider future load : If you suspect you’ll add EV chargers, shop tools, or big HVAC later, going with 1/0 aluminum is usually the “no‑regrets” choice for a 100 amp feeder.
  • Hire a licensed electrician : Sizing, grounding, bonding, and terminations are critical to avoid overheating or fire.

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Bottom note:
Information gathered from public forums or data available on the internet and portrayed here.