Based on the 2023 NEC, the ampacity of the copper wire in the size 3 AWG is:

• 60°C(140°F)(NM-B, UF-B): 85 amps
• 75°C (167°F) (THW, THWN, SE, USE, XHHW): 100 amps
• 90°C (194°F) (THWN-2, THHN, XHHW-2, USE-2): 115 amps

For aluminum 3 gauge wire, the ampacity is:

• 60°C (140°F): 65 amps
• 75°C (167°F): 75 amps
• 90°C (194°F): 85 amps

The common diameter of 3 AWG wire is 5.83 mm (0.2294 inches ) for copper and 6.47 mm (0.2546 inches) for aluminum.

Common applications of 3 AWG wire

3 AWG cables are designed for applications requiring high current capacity, including main service panels, large subpanels, and heavy-load circuits in residential, commercial, and light industrial settings. Here are some of the most common applications of 3 AWG wire:

Subpanels and main panels

• Used for connecting subpanels to main breaker panels in residential and commercial buildings (In a range of 60 to 125 Amps).
• Suitable for feeding main panels in smaller setups (100-115 Amps).

Heavy-duty appliances

• Powers heavy-duty electrical appliances like air conditioners, electric water heaters, and industrial machinery.
• Ideal for applications with high amperage, such as large ovens or electric dryers. The common range is 30 to 60 amps.

Feeders and branch circuits

• Used for feeder circuits in commercial buildings. It usually supplies power from the main distribution panel to smaller panels or junctions.
• Suitable for large branch circuits that require more current capacity than typical household circuits.

Service entrance cable (SE)

• Used to bring power from the utility meter to the main panel.

Solar power systems

• Used in photovoltaic (PV) systems for connecting solar arrays to inverters or battery storage systems.
• Suitable for handling the DC current produced by solar panels and delivering it to the inverter.

Electric vehicle (EV) charging stations

• Used in level 2 EV chargers in both residential and commercial setups.
• Can handle the increased amperage demand typical of higher-capacity EV charging units (newer DC fast-charging units).

Popular types of 3 AWG wire

• Usage: General-purpose building wire.
• Features: Thermoplastic High Heat-Resistant Nylon-coated; rated for both dry and wet locations. THWN-2 is the more advanced version, rated for wet environments and higher temperatures (up to 90°C in wet conditions).
• Application: Used in conduit in feeders and branch circuits. Copper and aluminum options are available.

• Usage: Residential, commercial, and industrial wiring.
• Features: Cross-linked High Heat-Resistant Water-Resistant; suitable for wet and dry locations and rated for up to 90°C in both.
• Application: XHHW-2 is also used in feeder and branch circuits, especially in environments where moisture resistance is important. 

• Usage: Suitable for residential, commercial, and industrial power distribution, including underground and outdoor installations.
• Features: Double-rated for both USE-2 (Underground Service Entrance) and RHH/RHW-2 applications. Has rubber (thermoset) insulation, and it is UV and moisture-resistant. Supports high heat up to 90°C in both wet and dry conditions. Available in both copper and aluminum versions.
• Application: Ideal for underground service entrances, direct burial, and feeder cables in outdoor or underground environments. It is also suitable for above-ground service, feeder, and branch circuits where resistance to heat, moisture, and sunlight is critical.

• Usage: Residential service entrances.
• Features: Contains multiple conductors, including a neutral and ground, and is used to connect the utility meter to the primary service panel.
• Application: SER is Suitable for above-ground service entrance applications and sub-panel wiring. 

• Usage: Machine tool wiring and internal wiring for appliances.
• Features: Flexible, moisture and oil-resistant; rated for up to 90°C.
• Application: 3 AWG MTW is used in industrial machinery wiring.

• Usage: Commercial and industrial settings.
• Features: Has a metallic sheath for added protection; suitable for areas where cables are exposed or require extra mechanical protection.
• Application: Frequently used for feeders and branch circuits in commercial buildings. Copper and aluminum versions are available.

• Usage: Solar power installations.
• Features: Can be exposed to sunlight and outdoor conditions; rated for 90°C in wet conditions and 150°C in dry.
• Application: Used to connect solar panels and components in photovoltaic systems. Copper and aluminum versions are available.