For a standard 240V residential electric dryer, use a 30-amp double-pole circuit breaker paired with 10 AWG copper wire. This is the definitive baseline for 95% of home dryers drawing up to 5,000 watts. Anything smaller will trip; anything larger violates NEC small-conductor protection rules.
The Baseline: 30-Amp Breaker and 10 AWG Copper
Most residential electric dryers operate on a 240V split-phase circuit and draw between 22 and 26 amps when the heating element and drum motor run simultaneously. A 30-amp double-pole breaker provides a maximum theoretical capacity of 7,200 watts (240V × 30A), giving the appliance the necessary headroom for startup inrush currents without nuisance tripping.
While the breaker protects the wire from melting, the wire must be sized to handle the continuous thermal load. For standard runs under 50 feet, 10 AWG copper is the undisputed standard. However, stating "10 AWG" without defining the installation environment is an invitation for a failed inspection. Wire ampacity is not a fixed number; it is a variable dependent on insulation type, termination temperature ratings, and ambient heat.
Sizing Assumptions and the NEC Ampacity Table
Before pulling wire, you must establish your baseline assumptions. The 30A/10 AWG rule relies on specific conditions outlined in NFPA 70 (NEC).
- Conductor Material: Copper (Cu)
- Temperature Column: 75°C (Standard for modern breakers and NEMA 14-30 receptacles)
- Ambient Temperature: 30°C (86°F) or lower
- Conduit/Cable Type: NM-B (Romex) or individual THHN conductors in a raceway
- Conductor Count: Maximum of 3 current-carrying conductors in the raceway
When you look at NEC Table 310.16, you will see that 10 AWG copper in the 90°C column is rated for 40 amps, and in the 75°C column, it is rated for 35 amps. So why do we cap it at a 30-amp breaker?
The answer lies in NEC Article 240.4(D), the "Small Conductor Rule." This rule explicitly overrides the ampacity table for overcurrent protection. It states that unless specific exceptions apply (like motor circuits), the overcurrent protection for 10 AWG copper shall not exceed 30 amps. Even though the wire's insulation can technically handle 35A or 40A of heat, the physical mass of the copper at 10 AWG is deemed insufficient to safely clear a fault on a larger breaker before sustaining damage.
| Wire Size (AWG) | 75°C Ampacity | 90°C Ampacity | Max Breaker (NEC 240.4D) | Dryer Application |
|---|---|---|---|---|
| 12 AWG | 25A | 30A | 20A | Too small (will trip) |
| 10 AWG | 35A | 40A | 30A | Standard Baseline |
| 8 AWG | 50A | 55A | 40A | Long runs / Voltage drop |
Voltage Drop: When Distance Forces a Wire Upgrade
Ampacity tells you if the wire will melt; voltage drop tells you if the appliance will actually function correctly. The NEC recommends a maximum voltage drop of 3% for branch circuits. For a 240V dryer, 3% equals a 7.2-volt drop.
Let's run the math using the standard voltage drop formula: VD = (2 × K × I × D) / CM.
- K (Copper resistivity at 75°C) = 12.9
- I (Current) = 24A (Using 80% of the 30A breaker rating for conservative continuous load calculation)
- D (One-way distance) = Variable
- CM (Circular mils for 10 AWG) = 10,380
Scenario A: 50-Foot Run
VD = (2 × 12.9 × 24 × 50) / 10,380 = 2.98V (1.24% drop). This is well within limits. 10 AWG is perfectly fine.
Scenario B: 100-Foot Run
VD = (2 × 12.9 × 24 × 100) / 10,380 = 5.96V (2.48% drop). Still under the 3% threshold. 10 AWG is acceptable, but approaching the limit.
Scenario C: 150-Foot Run (e.g., Panel in the basement, laundry on the far end of the second floor)
VD = (2 × 12.9 × 24 × 150) / 10,380 = 8.94V (3.72% drop). This exceeds the 3% recommendation. The dryer's heating element will run cooler, taking significantly longer to dry clothes, and the motor may overheat due to low voltage.
The Fix: You must upgrade to 8 AWG copper wire. Because 8 AWG has a circular mil area of 16,510, the voltage drop at 150 feet falls to 2.3%. You will still terminate this 8 AWG wire onto the same 30-amp breaker and 30-amp receptacle (the terminals on a 30A device are generally rated to accept up to 8 AWG wire; always verify the manufacturer's spec sheet, such as those from Schneider Electric / Square D).
Decision Tree: Choosing Your Exact Breaker and Wire
Use this decision matrix to lock in your exact materials list before heading to the supply house. This assumes standard residential 240V electric dryers (not gas dryers, which only require a 15A/120V circuit for the motor and controls).
| Installation Scenario | Breaker Size | Wire Size (Copper) | Wire Size (Aluminum) | Receptacle |
|---|---|---|---|---|
| Standard run (< 100 ft), normal ambient temp | 30A Double-Pole | 10 AWG | 8 AWG | NEMA 14-30R |
| Long run (100 ft - 150 ft) | 30A Double-Pole | 8 AWG | 6 AWG | NEMA 14-30R |
| Extreme run (> 150 ft) | 30A Double-Pole | 6 AWG | 4 AWG | NEMA 14-30R |
| Commercial Dryer / Laundromat (Check nameplate) | 40A or 50A | 8 AWG or 6 AWG | 6 AWG or 4 AWG | NEMA 14-50R |
A Note on Aluminum Wire: While copper is the standard for branch circuits, some regions use aluminum for cost savings. Aluminum has higher resistance and expands/contracts more under thermal cycling. For a 30-amp circuit, you must use a minimum of 8 AWG aluminum (rated 40A at 75°C). Never use 10 AWG aluminum for a 30A dryer circuit, and always apply an anti-oxidant compound (like Noalox) to the terminations to prevent high-resistance arcing over time.
Why You Cannot Downsize (and When to Call the AHJ)
A common DIY mistake is attempting to wire a dryer to an existing 20-amp double-pole breaker because "it's only pulling 22 amps." This fundamentally misunderstands breaker trip curves and NEC continuous load rules.
A 20-amp breaker is rated for a continuous load of only 16 amps (80% of 20A). At 240V, 16 amps equals 3,840 watts. When your 5,000-watt dryer kicks on, it pulls roughly 21 amps. A 20-amp breaker's thermal trip element will detect this 105% overload and will physically open the circuit within 10 to 30 minutes. You will spend your entire laundry cycle resetting the panel. Furthermore, NEC 240.4(D) forbids using 12 AWG wire (the standard for 20A) on a 30A breaker, making the "upgrade the breaker later" workaround a severe fire hazard.
What Changes the Answer?
The 30A/10 AWG baseline holds true unless you introduce derating factors. If you pull multiple circuits through the same conduit, NEC 310.15(C)(1) requires ampacity derating. If you have 4 to 6 current-carrying conductors in a single raceway, you must derate the ampacity to 80%.
- 10 AWG THHN (90°C column = 40A) × 0.80 = 32A.
- While 32A is technically above 30A, the 75°C termination limit drops 10 AWG to 35A. 35A × 0.80 = 28A.
- Because 28A is less than the 30A breaker rating, you must bump up to 8 AWG copper if bundling multiple dryer circuits in one conduit.
When an Engineer or AHJ Must Confirm
Stop and consult your local Authority Having Jurisdiction (AHJ) or a licensed electrical engineer if your project falls outside standard residential parameters:
- High Ambient Temperatures: If the conduit runs through an unventilated attic where temperatures regularly exceed 30°C (86°F), you must apply the temperature correction factors in NEC Table 310.15(B)(1). At 110°F, 10 AWG THHN must be derated by 87%, which may force an upgrade to 8 AWG.
- Commercial Laundry Spaces: Laundromats operate dryers continuously for 12+ hours. This triggers strict continuous-duty calculations and may require hardwired connections or 50-amp circuits depending on the specific commercial unit's nameplate data.
- Subpanel Feeder Limits: If you are adding a 30A dryer circuit to a 60A garage subpanel that is already heavily loaded by an EV charger, the main feeder to the subpanel may need upgrading. A panel load calculation is mandatory here.
By sticking to the 30-amp breaker and 10 AWG copper baseline—and upgrading to 8 AWG only when distance or bundling demands it—you ensure a safe, code-compliant circuit that will outlast the appliance itself.
