For a standard 240V residential electric dryer, you need a 30-amp double-pole breaker paired with 10 AWG copper wire (specifically 10/3 NM-B or THHN). If your dryer's nameplate exceeds 7,200 watts (30 amps), you must step up to a 40-amp breaker with 8 AWG copper wire.
The Baseline: 30A Breaker and 10 AWG Wire
Most residential electric dryers manufactured in the last two decades draw between 22 and 28 amps under peak heating load. The National Electrical Code (NEC) requires a dedicated branch circuit for laundry equipment. For the vast majority of homes, this means a 30-amp, 240-volt circuit.
- Conductor Material: Copper (Aluminum requires different sizing; see below).
- Temperature Column: 75°C (Standard for modern breakers and dryer receptacles).
- Ambient Temperature: 30°C (86°F) or lower.
- Installation Method: 10/3 NM-B cable in interior walls, or individual THHN conductors in EMT conduit.
- Load Type: Single dryer on a dedicated circuit (non-continuous load).
When sizing the wire, we look at NEC Table 310.16. In the 75°C column, 10 AWG copper has an allowable ampacity of 35 amps. However, you cannot put a 35-amp breaker on this wire. NEC Article 240.4(D) places a strict overcurrent protection limit on small conductors: 10 AWG copper is capped at a 30-amp breaker, regardless of its 35A or 40A (90°C column) insulation rating. This is a common trap for DIYers who read the ampacity table but miss the small-conductor override rules.
Sizing by Nameplate: The Decision Path
Never guess your dryer's electrical requirements based on physical size or age. Locate the manufacturer's nameplate (usually inside the door jamb or on the rear panel) and find the wattage or amperage rating. Use this decision tree to select your exact breaker and wire combination.
| Dryer Nameplate Rating | Calculated Amperage (W ÷ 240V) | Required Breaker Size | Required Copper Wire Size |
|---|---|---|---|
| Up to 7,200W | 30A or less | 30-Amp Double-Pole | 10 AWG (10/3 NM-B or THHN) |
| 7,201W to 9,600W | 30.1A to 40A | 40-Amp Double-Pole | 8 AWG (8/3 NM-B or THHN) |
| 9,601W to 12,000W | 40.1A to 50A | 50-Amp Double-Pole | 6 AWG (6/3 NM-B or THHN) |
Why Not One Size Smaller?
Circuit breakers are thermal-magnetic devices designed to protect the wire from melting, not to protect the appliance. If you attempt to run a 9,000W dryer (37.5A draw) on a 30-amp breaker with 10 AWG wire, the thermal element inside the breaker will trip within minutes of the heating cycle engaging. Conversely, if you install a 40-amp breaker on 10 AWG wire to stop the tripping, you create a severe fire hazard: the wire will overheat and melt its insulation long before the 40-amp breaker trips. The breaker must match the wire's protected ampacity, and the wire must exceed the appliance's maximum draw.
Voltage Drop and Long Wire Runs
Ampacity tables assume the wire can handle the heat generated by the current. They do not account for voltage drop over distance. The NEC recommends a maximum voltage drop of 3% for branch circuits to ensure appliances operate efficiently and motors do not overheat. On a 240V circuit, a 3% drop is 7.2 volts.
Let's run a voltage drop check for a standard 30A dryer circuit using 10 AWG copper wire. Using the standard voltage drop formula and referencing the Southwire Voltage Drop Calculator, 10 AWG copper carrying 30 amps drops approximately 0.0745 volts per foot of one-way run.
- At 50 feet: 3.72V drop (1.5%) — Perfectly acceptable.
- At 95 feet: 7.07V drop (2.9%) — Maximum limit for 10 AWG.
- At 120 feet: 8.94V drop (3.7%) — Exceeds 3% recommendation.
What Changes the Answer: Aluminum, Bundling, and Derating
The baseline assumptions dictate copper wire in a standard ambient environment. If your installation deviates from these conditions, the sizing must change.
Aluminum Conductors
Aluminum wire is cheaper but has higher resistance and lower ampacity than copper. You cannot use aluminum and copper interchangeably. For a 30-amp dryer circuit, 10 AWG aluminum is not recognized as a standard branch circuit size for this application. You must step up to 8 AWG aluminum (rated 40A in the 75°C column) to safely carry a 30-amp load. For a 40-amp dryer circuit, you must use 6 AWG aluminum. Always use anti-oxidant paste (like Noalox) on aluminum terminations and ensure your breaker and receptacle are explicitly rated for aluminum (marked AL/CU).
Conduit Bundling and Derating
If you are pulling THHN wires through EMT conduit and sharing that conduit with other circuits, you must apply NEC derating factors. If you have 4 to 6 current-carrying conductors in a single raceway, the allowable ampacity is reduced to 80%.
| Wire Size (Copper) | Base Ampacity (90°C Col) | Derated Ampacity (80% Factor) | Max Breaker Size After Derating |
|---|---|---|---|
| 10 AWG THHN | 40A | 32A | 30A |
| 8 AWG THHN | 55A | 44A | 40A |
Notice that 10 AWG THHN survives the 80% derating factor (32A is still above the 30A breaker limit). However, if you have 7 to 9 conductors in the conduit (70% derating), 10 AWG drops to 28A, meaning you can no longer use it on a 30-amp breaker. You would be forced to upsize to 8 AWG.
When the AHJ or an Engineer Must Confirm
While the decision tree above covers 95% of single-family residential dryer installations, certain scenarios require formal load calculations and sign-off from your local Authority Having Jurisdiction (AHJ) or a licensed professional engineer:
- Multi-Family Dwellings and Laundromats: If you are wiring a commercial laundromat or a shared apartment laundry room, dryers may be classified as continuous loads if they are expected to run for 3 hours or more. This requires sizing the circuit at 125% of the nameplate rating.
- Maxed-Out Service Panels: If adding a 30A or 40A dryer circuit pushes your total calculated load past your main breaker rating (e.g., adding a dryer to an older 100-amp service that already has central AC and an electric range), an engineer must perform an NEC Article 220 Optional Load Calculation to prove the service can handle the demand.
- Local Code Amendments: Some municipalities have strict local amendments regarding NM-B cable in certain wall cavities or specific grounding requirements for laundry areas. Always pull a permit and have the rough-in inspected before closing the drywall.
For a standard home renovation, check your dryer nameplate. If it says 6,800W, buy a 30-amp double-pole breaker, a roll of 10/3 NM-B, and a NEMA 14-30R receptacle. If it says 8,500W, buy a 40-amp breaker, 8/3 NM-B, and a NEMA 14-50R receptacle. Match the wire to the breaker, match the breaker to the load, and verify your run length for voltage drop.
