Calculator inputs
Choose a lookup, recommendation, or comparison workflow. Advanced inputs may remain at their documented defaults.
Ampacity lookup table
Search the active reference profile. Values shown are unadjusted base ampacities before project factors.
| Cable size | Area | Copper 60°C | Copper 75°C | Copper 90°C | Aluminium 60°C | Aluminium 75°C | Aluminium 90°C |
|---|---|---|---|---|---|---|---|
| 14 AWG | 2.08 mm² | 15 A | 2 A | 25 A | N/A A | N/A A | N/A A |
| 12 AWG | 3.31 mm² | 2 A | 25 A | 3 A | 15 A | 2 A | 25 A |
| 10 AWG | 5.26 mm² | 3 A | 35 A | 4 A | 25 A | 3 A | 35 A |
| 8 AWG | 8.37 mm² | 4 A | 5 A | 55 A | 35 A | 4 A | 45 A |
| 6 AWG | 13.3 mm² | 55 A | 65 A | 75 A | 4 A | 5 A | 55 A |
| 4 AWG | 21.2 mm² | 7 A | 85 A | 95 A | 55 A | 65 A | 75 A |
| 3 AWG | 26.7 mm² | 85 A | 1 A | 115 A | 65 A | 75 A | 85 A |
| 2 AWG | 33.6 mm² | 95 A | 115 A | 13 A | 75 A | 9 A | 1 A |
| 1 AWG | 42.4 mm² | 11 A | 13 A | 15 A | 85 A | 1 A | 115 A |
| 1/0 AWG | 53.5 mm² | 125 A | 15 A | 17 A | 1 A | 12 A | 135 A |
| 2/0 AWG | 67.4 mm² | 145 A | 175 A | 195 A | 115 A | 135 A | 15 A |
| 3/0 AWG | 85 mm² | 165 A | 2 A | 225 A | 13 A | 155 A | 175 A |
| 4/0 AWG | 107.2 mm² | 195 A | 23 A | 26 A | 15 A | 18 A | 205 A |
| 250 kcmil | 126.7 mm² | 215 A | 255 A | 29 A | 17 A | 205 A | 23 A |
| 300 kcmil | 152 mm² | 24 A | 285 A | 32 A | 195 A | 23 A | 26 A |
| 350 kcmil | 177.3 mm² | 26 A | 31 A | 35 A | 21 A | 25 A | 28 A |
| 400 kcmil | 202.7 mm² | 28 A | 335 A | 38 A | 225 A | 27 A | 305 A |
| 500 kcmil | 253.4 mm² | 32 A | 38 A | 43 A | 26 A | 31 A | 35 A |
| 600 kcmil | 304 mm² | 35 A | 42 A | 475 A | 285 A | 34 A | 385 A |
| 700 kcmil | 354.7 mm² | 385 A | 46 A | 52 A | 315 A | 375 A | 425 A |
| 750 kcmil | 380 mm² | 4 A | 475 A | 535 A | 32 A | 385 A | 435 A |
| 800 kcmil | 405.4 mm² | 41 A | 49 A | 555 A | 33 A | 395 A | 445 A |
| 900 kcmil | 456 mm² | 435 A | 52 A | 585 A | 355 A | 425 A | 48 A |
| 1000 kcmil | 506.7 mm² | 455 A | 545 A | 615 A | 375 A | 445 A | 5 A |
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Formula used
The adjusted ampacity is calculated from the selected base value and every enabled correction factor:
Iadjusted = Ibase × KT × KG × KM × KS × KD × KA × KH × Kcustom
Total capacity equals adjusted ampacity per conductor multiplied by parallel runs. The result is capped by the selected equipment terminal temperature column.
For single-phase AC and DC, voltage drop uses approximately 2 × L × I × (R cos φ + X sin φ) ÷ 1000. Three-phase calculation replaces 2 with √3.
The preliminary short-circuit check uses S = I √t ÷ k, where S is area, I is fault current, t is clearing time, and k reflects conductor and insulation limits.
How to use this calculator
- Select the governing standard workflow and edition enforced for the project location.
- Choose AWG, kcmil, metric, or custom manufacturer cable data.
- Select conductor material, insulation, terminal rating, construction, and parallel runs.
- Describe installation, ambient conditions, grouping, harmonics, and thermal environment.
- Enter current directly or calculate it from power, voltage, phase, power factor, and efficiency.
- Enter one-way route length and the maximum permitted voltage drop.
- Enable fault withstand and conduit-fill checks when verified inputs are available.
- Calculate, review every warning, and compare suggested compliant conductor options.
- Export the result, then verify it against authoritative tables and manufacturer instructions.
Example input data
| Example | System | Load | Installation | Key concern |
|---|---|---|---|---|
| Residential feeder | 230 V single-phase | 60 A continuous | Three loaded conductors in raceway | Terminal rating and continuous-load sizing |
| Industrial motor | 400 V three-phase | 45 kW at 0.86 power factor | Open tray with multiple circuits | Starting current, grouping, and protection |
| Buried feeder | 415 V three-phase | 180 A design current | Underground duct bank | Soil resistivity, depth, and voltage drop |
| Solar battery circuit | 120 V DC | 24 kW | Rooftop conduit | High temperature and continuous current |
Understanding cable ampacity decisions
Start with the correct reference
Ampacity is not a permanent number attached only to conductor size. It is a thermal limit that belongs to a complete installation. The selected table must match conductor material, insulation class, wiring method, voltage range, and code edition. A value copied from an unrelated chart can look reasonable while remaining unsafe. Record the table source, edition, cable marking, and equipment listing before accepting any result.
Apply temperature and grouping carefully
Cables release heat into surrounding air, soil, conduit, insulation, and nearby conductors. High ambient temperature reduces cooling. Bundled loaded conductors also warm each other, so grouping can create a substantial reduction. The insulation temperature rating may permit calculations from a higher column, yet the final ampacity cannot ignore lower-rated terminals. Neutral conductors carrying nonlinear harmonic current may need treatment as loaded conductors. Unknown thermal conditions should produce conservative assumptions and a visible warning.
Separate ampacity from voltage drop
A conductor can carry current safely and still deliver unacceptable voltage at the load. Long routes, low system voltage, poor power factor, high resistance, and motor starting current can require a larger cable. Voltage-drop calculations need one-way route length, conductor resistance at operating temperature, reactance, phase arrangement, and parallel-path information. The selected cable should satisfy both thermal capacity and performance limits. Sensitive equipment, emergency systems, motors, and remote loads may require stricter project limits.
Check faults and protective devices
Normal-load ampacity does not prove that a cable survives a short circuit. The adiabatic method compares conductor area with fault current, clearing time, material, and insulation temperature limits. Protective-device settings must also coordinate with cable capacity and load requirements. A breaker above adjusted ampacity normally needs correction, a larger conductor, or a specifically permitted exception. Motor, transformer, tap, welding, fire-pump, photovoltaic, and battery circuits can follow special rules that a general lookup cannot decide automatically.
Review physical installation limits
Conduit fill, bending space, pulling tension, termination range, lug material, cable diameter, tray loading, and parallel-conductor rules can reject an otherwise adequate electrical size. Aluminium conductors usually need larger areas and compatible terminations, yet they may reduce weight and cost. Parallel runs require matching length, material, size, insulation, termination, and routing. Underground work additionally depends on soil thermal resistivity, burial depth, duct spacing, moisture, and possible soil drying.
Use results as documented engineering evidence
Save all inputs, factors, assumptions, warnings, and source references with the design record. Compare the result with manufacturer software when using special cables, dense duct banks, thermal insulation, harmonics, or unusual duty cycles. Confirm the final selection with the authority having jurisdiction and a qualified electrical professional. Field conditions can differ from drawings, so installation inspection remains essential. Recalculate whenever routing, conductor count, ambient temperature, protective settings, cable type, or load changes.
A final review should also confirm phase balance, conductor identification, grounding arrangements, fire stopping, mechanical protection, accessibility, and maintenance needs. Document who approved each assumption and when source data was checked. Clear records help installers follow the design, help inspectors understand unusual choices, and make later load changes safer to evaluate and manage.
Frequently asked questions
What does cable ampacity mean?
Ampacity is the maximum current a conductor can carry continuously under stated conditions without exceeding its permitted temperature. Conditions include insulation, installation method, ambient temperature, grouping, terminals, and surrounding materials.
Why can two cables of the same size have different ratings?
Different insulation systems, conductor materials, installation methods, cable constructions, and temperature limits release heat differently. Manufacturer listings and code tables therefore assign different capacities to apparently similar conductor sizes.
Should I use the 60°C, 75°C, or 90°C column?
Use the column allowed by conductor insulation, equipment terminals, conductor-size rules, and the adopted code. Higher-temperature insulation can support derating calculations, but it does not automatically raise lower-temperature terminal ratings.
Does a neutral count as a current-carrying conductor?
It depends on the system and load. A neutral carrying only balanced-load imbalance may receive different treatment. A neutral carrying nonlinear harmonic current can be significantly loaded and may need counting.
Why does bundling reduce ampacity?
Loaded conductors heat nearby conductors and restrict heat escape. The resulting higher operating temperature requires an adjustment factor unless spacing, installation rules, or a verified engineering calculation permits another treatment.
Is voltage drop included in ampacity?
No. Ampacity is primarily a thermal current limit. Voltage drop is a separate performance check based on current, route length, resistance, reactance, power factor, circuit type, and parallel paths.
Can I place a larger breaker on the calculated cable?
Normally the protective device must coordinate with conductor ampacity. Some applications have specific exceptions, but they require the exact adopted rule, equipment characteristics, and qualified design review. Never assume an exception applies.
How are parallel conductors handled?
The calculator multiplies adjusted per-run ampacity and divides path impedance by parallel runs. Actual installations must satisfy rules for minimum size, equal characteristics, routing, terminations, and current sharing.
What is the adiabatic short-circuit check?
It estimates the conductor area needed to withstand thermal energy during a fault until protection clears. It uses fault current, clearing time, conductor material, insulation limits, and an appropriate verified k value.
Can this calculator design underground duct banks?
It provides preliminary soil, depth, grouping, and temperature factors. Dense duct banks often require detailed thermal calculations using actual geometry, load diversity, soil properties, cable losses, and manufacturer software.
Are the built-in values legally authoritative?
No. They are reference values for preliminary evaluation. The adopted electrical code, official amendments, cable manufacturer data, equipment listings, project specifications, and authority having jurisdiction control the final design.
Safety and compliance notice
This tool supports preliminary engineering and lookup work only. Electrical design can cause fire, shock, arc-flash, equipment damage, or loss of life when conditions are entered incorrectly. Verify all results with authoritative code tables, manufacturer data, equipment listings, project specifications, and a qualified electrical professional before procurement or installation.
Generated by Cable Ampacity Lookup Calculator. Verify every result before construction.