4 AWG (American Wire Gauge) wire specifications: 5.1894 mm diameter, 21.1506 mm² area, 85A ampacity (copper, 75°C). Resistance, weight, and common uses.
| Diameter | 5.1894 mm · 0.204307" · 204.31 mils |
| Cross-sectional area | 21.1506 mm² · 41,741 circular mils |
| Resistance (copper, 20°C) | 0.8151 Ω/km · 0.2484 Ω/1000ft |
| Resistance (aluminum, 20°C) | 1.3362 Ω/km · 0.4073 Ω/1000ft |
| Ampacity — copper 60°C | 70 A |
| Ampacity — copper 75°C | 85 A |
| Ampacity — copper 90°C | 95 A |
| Ampacity — aluminum 75°C | 65 A |
| Weight (copper) | 189.51 kg/km · 127.345 lbs/1000ft |
| Weight (aluminum) | 57.107 kg/km · 38.374 lbs/1000ft |
| Closest IEC 60228 size | 25 mm² |
| Skin depth at 60 Hz | 8.531 mm |
| Type | Temperature | Description |
|---|---|---|
| THHN/THWN-2 | 90°C dry / 75°C wet | Most common for building wire |
| XHHW-2 | 90°C dry and wet | Cross-linked polyethylene, moisture resistant |
| USE-2 | 90°C | Underground service entrance |
| NM-B (Romex) | 90°C | Non-metallic sheathed cable for residential |
| UF-B | 60°C | Underground feeder, direct burial |
4 AWG copper is commonly used for 60–70A subpanel feeders. NEC Table 310.16 rates it 85A at 75°C. It measures 5.189 mm in diameter with a 21.2 mm² cross-section.
Per NEC Table 310.16 (30°C ambient, no more than three current-carrying conductors), 4 AWG copper is rated 70A at 60°C, 85A at 75°C and 95A at 90°C. 4 AWG aluminum is rated 55A, 65A and 75A in the same columns. On circuits of 100A or less, NEC 110.14(C) generally requires the 60°C column unless every termination is rated 75°C.
Yes. 4 AWG aluminum is rated 65A at 75°C versus 85A for copper, so matching the copper rating takes 2 AWG aluminum. Aluminum at this size is common for feeders, subpanels and service conductors (SER, USE-2, XHHW-2). Use AL-rated lugs, torque to the manufacturer’s spec and apply antioxidant compound where required.