What Size Wire for 30 Amps? — Complete NEC Guide
For a 30 amp circuit, you need 10 AWG copper wire or 8 AWG aluminum wire per NEC Table 310.16. Use a 30A breaker. Here is the complete sizing guide with distances, costs, and professional tips.
Common Uses for 30 Amp Circuits
Electric dryers (240V), window AC units (240V), small water heaters, welders, RV hookups. These applications require a dedicated 30A breaker and 10 AWG copper wire (or 8 AWG aluminum for longer runs or cost savings).
The wire size is determined by NEC Table 310.16, which lists the maximum allowable ampacity for each conductor size based on insulation temperature rating and conductor material. For 30 amps, the minimum conductor size at 75°C insulation (the most common rating for modern wire) is 10 AWG for copper and 8 AWG for aluminum.
Maximum Wire Run Distance
Wire gauge determines not just ampacity but also voltage drop over distance. For a 30 amp load:
At 240V: 75 ft with 10 AWG. At 120V: N/A (typically 240V).
If your wire run exceeds these distances, you must upsize the wire by one or two gauges to keep voltage drop under the NEC-recommended 3% for branch circuits. Use our Voltage Drop Calculator to check your specific run.
NEC Code Reference
The 30 amp wire size requirement comes from NEC Table 310.16, 240.4(D). This table provides ampacity ratings for insulated conductors rated 0 through 2000 volts, 60°C through 90°C, not more than three current-carrying conductors in raceway, cable, or earth. For ambient temperatures above 30°C (86°F), derating factors from NEC Table 310.15(B)(1) must be applied.
Dryer Circuit Wiring
Modern electric dryers require a 30A, 240V circuit with 10/3 NM-B cable (3 conductors + ground). The NEMA 14-30 receptacle replaced the older NEMA 10-30 — new installations must include a separate equipment ground per NEC 250.140.
Conduit vs. Romex Installation
For residential work, NM-B 10/3 with ground (for 240V) is the standard choice for concealed wiring in walls and attics. For exposed runs in garages, basements, or outdoors, use THHN 10 AWG in EMT or PVC conduit. In commercial and industrial settings, individual THHN 10 AWG conductors in conduit are standard.
When running in conduit with more than 3 current-carrying conductors, ampacity must be derated per NEC 310.15(C). This means the effective ampacity of 10 AWG may be less than 30A, requiring you to upsize. Use our Derating Calculator to check.
Wire Cost Estimate
10 AWG copper wire costs approximately $0.45-0.70 per foot for NM-B (Romex) cable. For a typical 50-foot run, expect to spend $25-90 on wire alone, plus breaker ($5-15), box, connectors, and labor if hiring an electrician. Aluminum wire costs roughly 40-60% less than copper for equivalent ampacity but requires larger gauge sizes.