What kind of load is it?
Ordinary branch circuit, continuous load, motor, HVAC, EVSE, welder, RV, or another special application?
30 amp wire size · updated August 2026
What Size Wire for a 30 Amp Breaker? NEC & IEC Guide
For many ordinary U.S. branch circuits, 10 AWG copper is the familiar starting point. For a general 30A circuit using aluminum or copper-clad aluminum, 8 AWG is the common starting size. These are starting points—not permission to skip the load, cable, temperature, length, equipment, terminal, and local-code checks.
10 AWG copperCommon NEC starting point for an ordinary 30A branch circuit.
8 AWG Al / Cu-clad AlGeneral starting point because 10 AWG is usually limited to 25A.
24A all-continuous loadCommon result when no noncontinuous load is present and the usual 125% sizing method applies.
No fixed distance cutoffCalculate voltage drop; “over 100 ft means 8 AWG” is not a code rule.
Photo: Shixart1985 / Wikimedia Commons, CC BY 2.0; cropped and darkened for this page. The scene shows a control panel, not a verified 30A circuit or a SENTOP installation. No endorsement is implied.
Quick decision
Answer five questions before you choose a conductor
A breaker number is only one input. If any answer is unknown, the wire size is not ready for approval.
What is the conductor system?
Copper, aluminum, or copper-clad aluminum; cable or raceway; dry, wet, underground, or equipment wiring?
Which temperature limit applies?
Check insulation, cable rules, breaker lugs, terminal blocks, equipment terminals, ambient heat, and grouping.
How long is the complete path?
Use one-way route length as an input, then apply the correct complete-current-path or phase factor with actual load, voltage, conductor data, and power factor.
Which code and instructions govern?
NFPA 70 is a U.S. model code. The locally adopted edition, amendments, authority having jurisdiction, and equipment instructions control the final installation.
Direct answer
Start with 10 AWG copper—but finish the full check
For an ordinary U.S. 30A branch circuit using copper conductors, 10 AWG is the common starting size. For a general 30A circuit using aluminum or copper-clad aluminum, 8 AWG is the common starting size because NEC 240.4(D) generally limits 10 AWG aluminum or copper-clad aluminum to 25A.
The word starting matters. A hot location, too many current-carrying conductors, a long run, a special equipment rule, a lower-rated termination, or an unsuitable cable can require a different design. The breaker, conductor, terminals, load, and wiring method must work as one system.
Do not select from the 75°C or 90°C column alone.
A 90°C insulation marking does not turn 10 AWG copper into a general 40A branch-circuit conductor. Small-conductor protection limits and termination rules still apply.
NEC reference
Read Table 310.16 together with 240.4(D)
The table values below are reference ampacities, not automatic breaker permissions. The table assumes no more than three current-carrying conductors in a raceway, cable, or earth and a 30°C ambient before applicable corrections and adjustments.
| Conductor | 60°C column | 75°C column | 90°C column | General small-conductor protection result |
|---|---|---|---|---|
| 12 AWG copper | 20A | 25A | 30A | Generally limited to 20A; not the ordinary choice for a 30A breaker. |
| 10 AWG copper | 30A | 35A | 40A | Generally limited to 30A; familiar copper starting point. |
| 10 AWG Al / Cu-clad Al | 25A | 30A | 35A | Generally limited to 25A; the 75°C cell does not make it a general 30A answer. |
| 8 AWG Al / Cu-clad Al | 35A | 40A | 45A | Common general starting point for 30A, subject to the complete installation. |
| 8 AWG copper | 40A | 50A | 55A | Possible upsize for voltage drop or corrected ampacity; the breaker and equipment design still control. |
The 2024 IRC Chapter 37 provides publicly readable NEC-derived residential tables showing the 30A copper/aluminum baselines and small-conductor limits. Use NFPA 70 public access to check the current model code, then apply the edition and amendments actually adopted for the project. Specific permitted applications can use different rules.
Continuous load
The “80% rule” is really a 125% sizing check
A continuous load is a load whose maximum current is expected to continue for three hours or more. Under the usual method for an assembly not listed for operation at 100% of its rating, branch-circuit conductors and overcurrent protection are sized for 100% of the noncontinuous load plus 125% of the continuous load. With no noncontinuous load, 24A is the familiar all-continuous result for a 30A circuit.
Do not describe this as a fixed percentage limit on the conductor itself. Listed 100%-rated assemblies, equipment articles, and local rules can change the method.
All-continuous example24A × 125% = 30AWith no noncontinuous load, 24A leads to a 30A sizing basis when the usual method applies.
True 30A continuous load30A × 125% = 37.5AThis load cannot simply stay on an ordinary 30A circuit. Complete the required conductor and OCPD selection.
The ordinary sizing method is shown in IRC E3701.2.1. See Eaton’s 2026 continuous-load explanation for the current NEC update. Always check whether a listed 100%-rated assembly or equipment-specific article changes the ordinary method.
Ampacity conditions
Six checks can change the minimum size
Ampacity is not a permanent number printed beside an AWG size. It belongs to a conductor installed under stated conditions.
Installation method first
“10 AWG” does not identify a complete cable system
Type NM-B, individual raceway conductors, wet-location conductors, underground cable, flexible cable, and machine wiring do not share one use condition. Select the wiring method for the location before applying its ampacity rules.
- NM-B: its ampacity cannot exceed the 60°C column. The 90°C rating may be used for adjustment or correction only when the final result does not exceed the 60°C ampacity.
- Individual conductors: a THHN/THWN-2-marked conductor normally needs an approved raceway or equipment wiring method. Read the full marking; wet locations require an appropriate wet rating.
- Wet, buried, hot, or chemical areas: select an approved cable and insulation system for that environment. A larger gauge does not repair the wrong cable type.
Use the exact cable marking and installation rules. The UL Wire and Cable Marking Guide explains why material, location, and temperature markings matter.
Ambient temperature
Hot attics, rooftops, machinery, and tightly packed enclosures can lower usable ampacity.
Apply the code’s temperature correction for the actual conductor rating and location.Conductor count
More than three current-carrying conductors together can require an ampacity adjustment.
Count conductors by the governing rule, not simply by cable color.Termination temperature
Breaker lugs, terminal blocks, and equipment terminals can force use of a lower temperature column.
The insulation’s highest number is not automatically the usable ampacity.Conductor material
Copper, aluminum, and copper-clad aluminum use different table values and connector conditions.
Use only terminals identified for the exact metal and conductor range.Load duty and harmonics
Continuous duty, nonlinear loads, imbalance, motors, and cycling can change the design calculation.
Use the equipment nameplate and the applicable equipment article.Local and product rules
The adopted code edition, local amendments, listing conditions, and manufacturer instructions all matter.
Document the exact basis instead of writing only “30A / 10 AWG.”
Voltage drop
There is no universal “100-foot rule”
A 10 AWG copper conductor may pass the ampacity check and still be upsized for voltage drop. “Use 8 AWG over 100 feet” is not a reliable rule. Record the actual one-way route, but use a calculation that accounts for the complete current path and the correct single-phase, three-phase, or DC relationship, plus actual load current, supply voltage, conductor resistance or impedance at operating temperature, and power factor where applicable.
The NEC’s familiar 3% branch-circuit and 5% feeder-plus-branch figures appear in informational notes as reasonable-efficiency guidance. They are not a blanket mandatory limit for every installation, although a specific code section, project specification, or local rule can make a limit enforceable.
At the same current, voltage alone does not change a conductor’s thermal ampacity; circuit configuration still can.
Voltage changes power, equipment and insulation requirements, conductor arrangement, and voltage-drop percentage. For otherwise identical two-wire circuits at the same current, the voltage drop in volts is the same; as a percentage, it is twice as large at 120V as at 240V.
Route and path factor
Record one-way route length, then apply the correct complete-path or phase factor.
Load current
Use the expected operating load, not only the breaker handle rating.
Voltage and circuit
Record 120/240V, single- or three-phase, AC or DC, and conductor arrangement.
Conductor data
Use material, size, resistance/impedance, temperature, and installation data.
Load performance
Check acceptable terminal voltage, starting behavior, control stability, and project limits.
Use SENTOP’s electrical calculators or the Southwire voltage-drop calculator with real project inputs. For conductor and terminal-fit context, use the AWG guide without treating AWG-to-mm² conversion as approval.
Application rules
A 30A breaker does not describe the equipment
Dryers, water heaters, HVAC equipment, EV charging, motors, welders, and RV supplies can all show “30A,” yet use different load and wiring rules.
Dryer or similar 120/240V load
Follow the nameplate, instructions, receptacle configuration, conductor count, grounding, and locally adopted appliance rules. A common 30A dryer circuit does not prove every dryer has the same needs.
Do not choose 10/2 versus 10/3 cable from amperes alone.Fixed storage water heater
For a fixed storage-type water heater with a capacity of 450 L (120 gal) or less, the NEC generally requires the branch-circuit overcurrent device and conductors to have an ampere rating of not less than 125% of the water heater’s ampere rating. Confirm the adopted edition, nameplate, and manufacturer instructions.
Calculate the load before selecting the breaker and conductor.Air conditioning or refrigeration
Size field conductors to at least the marked minimum circuit ampacity (MCA), after the required installation corrections, and do not exceed the marked maximum overcurrent protection (MOCP or MOP). The breaker-to-wire relationship can differ from an ordinary branch circuit.
A 30A MOCP does not mean the load is 30A or prove one universal gauge.Motor or welder
Starting current, overload protection, duty cycle, and short-circuit protection have dedicated code methods. A smaller-looking conductor beside a 30A breaker is not automatically wrong—or safe.
Identify the exact equipment article and protection scheme.EV supply equipment
EV charging is treated as continuous. Under the usual 125% method, a 30A circuit generally supports a 24A maximum continuous EVSE load.
Use the EVSE label, manufacturer instructions, and adopted code.30A recreational-vehicle supply
A NEMA TT-30 receptacle is a 30A, 125V travel-trailer device with line, neutral, and equipment ground. It is not a 240V dryer outlet. Supplying 240V can damage connected RV equipment and create a serious hazard.
Verify the receptacle pattern and equipment before selecting cable or protection.Battery, PV, vehicle, or control circuit
The 30A ampacity check is only one step. Verify DC voltage and polarity, the full current-path voltage drop, conductor and wiring-method rules, available fault current, and the DC ratings of the OCPD, disconnects, and terminals under the applicable system standard.
Never assume an AC device has the same DC voltage or interrupting rating.| Circuit or equipment | Insulated current-path conductors | What the cable label may mean | Decision boundary |
|---|---|---|---|
| 120V load | One ungrounded conductor plus neutral | “10/2 with ground” can provide two insulated 10 AWG conductors plus an equipment grounding conductor. | Confirm the equipment, approved wiring method, conductor material, and local rules. |
| 240V-only load | Two ungrounded conductors; no neutral when the equipment does not need one | “10/2 with ground” may serve this arrangement when 10 AWG copper and that cable type are approved. | Follow the equipment diagram. Never repurpose the equipment grounding conductor as neutral. |
| 120/240V load | Two ungrounded conductors plus neutral | “10/3 with ground” adds a third insulated conductor and is a common arrangement. | The breaker rating alone does not tell you whether a neutral is required. |
| NEMA TT-30 RV supply | Line plus neutral at 125V | Three-wire grounding configuration: line, neutral, and equipment ground | TT-30 is not 240V and is not interchangeable with a 14-30 dryer connection. |
For application-level context, see what appliances use a 30A circuit and SENTOP’s breaker-sizing guide. Cable designations above describe common U.S. arrangements, not worldwide approval. Final design must follow the equipment label and governing rules.
Connection compatibility
Wire size is only half of a safe 30A connection
A branch-circuit breaker provides overcurrent protection; it does not qualify every lug or terminal block in the current path or reliably detect every high-resistance connection. Approve the exact conductor and each receiving terminal together. This is especially important when changing from 10 AWG copper to 8 AWG copper or aluminum for voltage drop or corrected ampacity.
- Confirm conductor metal, AWG/mm², solid/stranded/fine-stranded class, ferrule or lug preparation, and insulation diameter.
- Check the exact terminal’s rated current, voltage, temperature conditions, conductor range, number of conductors per clamp, and required approval.
- Follow the model-specific wire preparation, strip length, tooling, and tightening torque where applicable. There is no universal torque for a “30A terminal.”
- Never remove strands to make an oversized conductor fit, and never place aluminum in a copper-only connector.
- Verify the available fault current, each protective device’s interrupting rating, and—where required—the SCCR of the complete assembly. Normal current rating and selective coordination are separate checks.
Part-number approval
A practical terminal and breaker proof list
Ask for evidence tied to the exact catalog number. A family brochure or a similar-looking connector is not enough.
Wire acceptance
Material, size, and conductor class
Verify Cu, Al, or copper-clad aluminum marking; AWG/mm² range; strand class; ferrule/lug permission; and insulation range.
Electrical rating
Current, voltage, and temperature basis
Keep UL, IEC, or other rating systems separate and use the conditions for the destination market and complete assembly.
Workmanship
Strip length, torque, and tooling
Follow the model-specific instructions and use the manufacturer-specified or suitably process-controlled tooling and torque method. See SENTOP’s terminal torque guide →
Panel integration
Mounting, accessories, and fault duty
Check rail or panel mounting, end plates, markers, jumpers, clearances, bend radius, enclosure, and applicable short-circuit evidence.
Regional boundary
NEC and IEC do not create one global 30A size
“10 AWG copper” is a useful U.S. answer, not a worldwide metric specification. Start with the destination country, installation standard, and cable system.
NEC-based project
Use the locally adopted NFPA 70 edition, Table 310.16 conditions, 240.4(D), correction and adjustment rules, equipment articles, product listings, and local amendments.
The authority having jurisdiction and equipment instructions control the final installation.Metric wiring system
IEC 60364-5-52 selects wiring systems by current-carrying capacity, installation method, correction factors, connections, and voltage drop. National adoptions can add or change requirements.
Do not round an AWG size to the nearest mm² and assume equal approval.End-equipment requirements
Machine, control-panel, appliance, vehicle, marine, renewable-energy, and other standards may use their own conductor and component rules in addition to installation codes.
Record the exact standard, certification, and destination market in the BOM and RFQ.Official IEC references: IEC 60364-5-52:2009+A1:2024 for wiring systems and IEC 60228:2023 for conductor classes. SENTOP can help compare component documentation through its standards and certificate support.
Safe workflow
Turn a quick answer into a documented design
This article is a planning guide, not live-work instruction. Installation and service belong to qualified people following the site electrical-safety program.
Classify the circuit
Record voltage, phase, AC/DC, load type, duty, breaker function, and the equipment article or end-product standard.
Do not start with gauge alone.Calculate the load
Separate continuous and noncontinuous current. Use the nameplate, MCA/MOCP, motor data, EVSE rating, or other governing input.
Do not use breaker size as a load measurement.Pass both wire checks
First verify corrected ampacity and protection. Then calculate voltage drop and load performance for the actual route.
Upsize only with terminal and enclosure fit confirmed.Approve every connection
Check breakers, lugs, terminal blocks, disconnects, equipment terminals, conductor count, torque, temperature, and fault duty.
A wire fitting physically is not approval.De-energize and verify
Before exposed work, de-energize the parts unless the governing safety rule specifically permits energized work. Disconnect every source, release or block stored electrical energy, apply the required lockout/tagout procedure, and have a qualified person use suitable test equipment to verify that exposed circuit elements and equipment parts are de-energized and free of induced voltage or unrelated backfeed. For circuits over 600V nominal, OSHA also requires the test equipment to be checked for proper operation immediately before and immediately after the test.
Treat the parts as energized until the required verification is complete.Safety basis for U.S. general-industry workplaces: OSHA 1910.333. Construction work can fall under OSHA 1926 and other rules; non-U.S. work must follow applicable local safety requirements. Employer procedures may be more restrictive.
Component matching
Send the data behind “30A”
SENTOP can help match a terminal block, breaker, and wiring component set to your documented requirement. This support does not replace the project engineer, governing code, or authority having jurisdiction.
Market & standardDestination country, adopted code, equipment standard, certification, and AHJ/project requirements.
CircuitAC/DC voltage, phase, maximum and continuous current, breaker/OCPD, available fault current, and load type.
ConductorCu/Al/Cu-clad Al, actual AWG/mm², solid/stranded/ferruled format, insulation marking, OD, and temperature.
InstallationCable or raceway, conductor count, route length, ambient, enclosure, mounting, pole count, and bend space.
ConnectionTerminal style, wire-entry direction, strip length or lug, torque process, accessories, drawing, and current model.
SupplyPrototype or production quantity, packaging, labeling, documentation, delivery country, and target date.
Continue the decision
Related SENTOP selection resources
Electrical calculators
Use the actual circuit inputs to check voltage drop and other design values.
Open the calculators →Protection selection guide
Build the protection decision from the load, system, fault duty, and market.
Use the guide →Miniature circuit breakers
Compare breaker families only after the circuit requirements are documented.
View MCB options →Distribution boxes
Coordinate the enclosure, devices, conductor space, and destination standard.
View distribution boxes →Choose the right breaker size
Review the wider load and protection process when the circuit is not fixed yet.
Read the sizing guide →What equipment uses 30A?
Separate appliance eligibility and nameplate needs from conductor sizing.
Review common loads →AWG wire sizing for terminals
Compare conductor range and terminal fit without treating conversion as approval.
Read the AWG guide →
Frequently asked questions
30 amp wire-size answers without the shortcuts
These answers describe common U.S. practice. The adopted code, equipment instructions, and local authority decide the final installation.
Is 10 AWG wire enough for a 30 amp breaker?
10 AWG copper is the familiar starting point for an ordinary U.S. 30A branch circuit. It is enough only when its corrected ampacity, cable type, termination temperature, load calculation, voltage drop, equipment rules, and local code all pass. Do not assume 10 AWG aluminum is equivalent.
Can I use 12 AWG copper on a 30 amp breaker?
Not for an ordinary 30A branch circuit. NEC 240.4(D) generally limits 12 AWG copper to 20A. Specific motor, HVAC, welder, or other permitted applications can use different conductor and overcurrent rules, so judge an existing installation by its exact equipment rule—not appearance alone.
Can 10 AWG aluminum be used on a 30 amp circuit?
Generally not for an ordinary 30A branch circuit. Although Table 310.16 shows 30A in the 75°C column, NEC 240.4(D) generally limits 10 AWG aluminum or copper-clad aluminum to 25A. A general 30A aluminum design commonly starts at 8 AWG, subject to all other conditions.
Do I automatically need 8 AWG copper over 100 feet?
No. There is no universal 100-foot cutoff. Record the actual one-way route, but calculate voltage drop with a method that accounts for the complete current path and the correct AC/DC and phase relationship, plus actual load current, voltage, conductor resistance or impedance at operating temperature, and required equipment voltage. Upsize if the result or project rule requires it, then recheck terminal, raceway, bend-space, and equipment-grounding-conductor requirements.
Does a 30 amp 120V circuit use the same wire as a 30 amp 240V circuit?
The same 30A current gives the same starting ampacity question, but the circuits are not interchangeable. Voltage changes power, conductor arrangement, receptacle and equipment type, and voltage-drop percentage. Follow the load instructions and circuit configuration for the actual equipment.
Do I need 10/2 or 10/3 cable for a 30 amp circuit?
Amperes alone do not decide. “10/2 with ground” normally has two insulated 10 AWG conductors plus an equipment grounding conductor and may suit a 120V or 240V-only arrangement when the equipment and wiring method allow it. “10/3 with ground” adds a third insulated conductor and is commonly used when 120/240V equipment needs two ungrounded conductors plus a neutral. Follow the exact equipment diagram and local code.
How much continuous load can a normal 30 amp circuit carry?
With no noncontinuous load, 24A of continuous load produces a 30A sizing basis under the usual method because 24A multiplied by 125% equals 30A. If noncontinuous load is also present, add it at 100% before comparing the total sizing basis with the circuit rating. An assembly listed for operation at 100% of its rating, a special equipment rule, or a local requirement can change the method.
Should I use NM-B or THHN/THWN-2 for a 30 amp circuit?
Use the wiring method approved for the location. NM-B is for normally dry locations and its ampacity cannot exceed the 60°C column. Individual THHN/THWN-2 conductors normally require an approved raceway or equipment wiring method, and the exact marking determines dry, damp, or wet-location use.
Can I upsize from 10 AWG to 8 AWG?
Often yes, while retaining the correctly selected 30A OCPD. Confirm that every termination, raceway, connector, enclosure, and bend space accepts the larger conductor. Also apply the adopted equipment-grounding-conductor rule: when ungrounded conductors are increased for voltage drop or another reason, a wire-type equipment grounding conductor may also have to be increased; correction- or adjustment-driven upsizing is treated differently.
Primary references
Official sources behind the selection rules
These primary and manufacturer sources support the decision points above. The enforceable rules remain the edition and amendments adopted by the local jurisdiction, together with the exact equipment instructions.
Have the wire size—now approve the complete connection
Send SENTOP the destination standard, circuit data, conductor marking, terminal format, mounting, environment, documentation, and quantity. We will help narrow the component options for your panel or equipment project.
