The Complete Aluminium Wire Size Chart & Ampacity Guide (NEC 310.16)

If you are sizing an aluminium wire size chart lookup for a standard 100-amp residential feeder, you need 1 AWG or 1/0 AWG aluminium (depending on termination temperature ratings). For a 200-amp residential service, the standard pick is 4/0 AWG aluminium. Sizing aluminium (often spelled aluminum in the US) requires strict attention to the National Electrical Code (NEC) temperature columns, as aluminium has a lower ampacity per cross-sectional area than copper and is highly sensitive to termination torque and oxidation.

This guide provides the exact data from NEC Table 310.16 for aluminium conductors, explains which temperature column legally applies to your specific installation, and provides a concrete decision path so you can buy the right wire without a second trip to the electrical supply house.

How to Read the Aluminium Wire Size Chart

Before looking at the numbers, you must understand the three temperature columns in the NEC ampacity tables. The chart below is sourced directly from NFPA 70 (National Electrical Code), specifically Table 310.16 for aluminium conductors with an ambient temperature of 30°C (86°F).

The 60°C Column: Use this column when your wire is NM-B (Romex) cable, or when your breakers and lugs are only rated for 60°C (common on older equipment or breakers rated 100A and below that lack a 75°C marking).
The 75°C Column: This is your default for most modern commercial and residential feeders. Use this when pulling THHN/THWN-2 or XHHW-2 aluminium wire through conduit, provided the breaker lugs and panelboard are explicitly rated for 75°C (standard on almost all modern equipment rated over 100A).
The 90°C Column: You almost never use this column for final ampacity. The 90°C column is used exclusively as the starting baseline for calculating derating factors (like ambient temperature or conduit fill). Your final derated ampacity must still be terminated based on the 60°C or 75°C limits of your lugs.

The Master Aluminium Ampacity Chart (NEC Table 310.16)

The following table lists the allowable ampacities for insulated aluminium conductors. Note that 8 AWG aluminium is rarely used in practice for branch circuits due to termination difficulties and local code restrictions; feeders typically start at 6 AWG or 4 AWG.

Derating: When the Chart Values Shrink

The numbers in the chart above assume two things: an ambient temperature of 86°F (30°C) or less, and no more than three current-carrying conductors in a single raceway (conduit). If your jobsite violates either assumption, you must derate the wire using the 90°C column as your starting point, according to Southwire's technical derating guidelines and NEC Article 310.15.

Ambient Temperature Derating: If your conduit is running across a hot roof or through an attic that reaches 110°F (43°C), you must multiply the 90°C ampacity by 0.87. For example, 4/0 AWG aluminium has a 90°C baseline of 205A. Multiplied by 0.87, the new ampacity is 178.3A. You must then check if 178.3A satisfies your 75°C termination requirements for your breaker.

Conduit Fill Derating: If you pull four to six current-carrying conductors in one conduit (e.g., two separate 240V circuits sharing a single PVC pipe), you must multiply the 90°C baseline by 80%. If you pull seven to nine conductors, you multiply by 70%. Neutral wires carrying only unbalanced load do not count; neutrals on non-linear loads (like multi-wire branch circuits with electronics) do count.

Decision Path: Picking Your Exact Aluminium Wire Size

Use this decision tree to terminate your sizing process with a single, concrete wire purchase. This assumes standard residential/commercial feeders in conduit (THHN/THWN-2 or XHHW-2) with modern 75°C rated lugs.

What This Chart Cannot Tell You (Voltage Drop & Terminations)

An ampacity chart only tells you the thermal limit of the wire insulation before it melts. It does not guarantee the equipment at the other end will function correctly. You must account for three physical realities that the NEC table ignores:

1. Voltage Drop over Distance: Aluminium has roughly 61% higher electrical resistance than copper. If you run a 4/0 AWG aluminium feeder 250 feet to a detached garage workshop, the ampacity is fine for a 200A breaker, but the voltage drop under a heavy 150A load will exceed 5%, causing motors to overheat and electronics to brown out. For runs over 100 feet, always run a voltage drop calculation. As a rule of thumb, upsize your aluminium wire by one AWG size for every 100 feet past the initial 50 feet.

2. NEC 110.14(C) Termination Limits: Even if you use 90°C rated XHHW-2 aluminium wire in a 110°F attic, the physical breaker lug you are screwing the wire into is likely only rated for 75°C. The NEC mandates that the final ampacity of the circuit cannot exceed the lowest temperature rating of any connected component. You can use the 90°C column to derate for heat, but the final derated number must still fit within the 75°C column limits of the breaker lug.

3. Oxidation and Torque: Aluminium oxidizes rapidly when exposed to air, creating a highly resistive layer that generates intense heat at termination points. The chart assumes a perfect connection. In the real world, you must wire-brush the aluminium conductor, apply an anti-oxidant compound (like Noalox or Deox), and use a calibrated torque screwdriver or wrench to tighten the lug to the exact inch-pound specification printed on the breaker label. Failure to do this will result in a melted lug, regardless of how perfectly you sized the wire.