Electrical reference chart
Wire Size Chart
Use this wire size chart after the calculator result to document why a conductor size was selected, which inputs controlled the result, and what must be checked before ordering wire or pulling a circuit.
Quick reference table
A wire size chart is useful only when it keeps the field sequence visible: calculated load first, usable ampacity second, terminal temperature and derating third, then voltage drop and equipment instructions. Use the calculator result as the starting point and verify the adopted NEC edition, manufacturer data, and AHJ requirements before treating the conductor as ready for the job.
Wire size field decision order
| Step | Record from the job | Why it can control size |
|---|---|---|
| Load basis | Calculated amps, voltage, phase, and continuous duty | Sets the minimum current the conductor must carry |
| Conductor family | Copper or aluminum, insulation type, raceway or cable method | Changes resistance, ampacity basis, and termination expectations |
| Termination limit | Equipment lug temperature rating and conductor material allowed | Can cap the usable ampacity below the insulation rating |
| Adjustment conditions | Ambient temperature, rooftop exposure, grouping, and current-carrying count | Can reduce the conductor ampacity used for planning |
| Performance check | One-way distance and project voltage-drop target | May make a larger conductor practical for long runs |
Common result-area follow-up checks
| Calculator result shows | Field question to answer | Next action |
|---|---|---|
| Ampacity controls | Are terminals, ambient, and bundling already reflected? | Review ampacity chart and document the limiting factor |
| Voltage drop controls | Is the run length or voltage-drop target driving a larger size? | Keep the larger size and note the performance basis |
| Aluminum selected | Are lugs listed and torque instructions available? | Verify equipment instructions before procurement |
| Borderline result | Would a future load or field routing change affect the selection? | Review spare capacity before the pull is scheduled |
How to use this chart
Start from the result, not memory
Use the calculator output as the job record, then confirm which input controlled the conductor size: load current, terminal rating, derating, or voltage drop.
Separate heat from performance
Ampacity protects the conductor from overheating, while voltage drop protects equipment performance. Keep both screens visible before calling the size acceptable.
Close with equipment notes
Before ordering conductor, document lug material, temperature rating, torque instructions, raceway plan, and any manufacturer requirements that affect the installation.
Formula basis
Conductor planning screen = calculated load plus duty factors, then compare usable ampacity, terminal limit, voltage-drop target, and equipment instructions.
- Calculated load is the amperes from the load schedule, nameplate, or calculator result.
- Usable ampacity is the conductor value after material, insulation, terminal temperature, ambient correction, and conductor-count adjustment are considered.
- Voltage drop is a performance screen that can require a larger conductor even when ampacity is acceptable.
Worked examples
Long 240 V feeder result
The calculator may show that the minimum ampacity size passes, but the voltage-drop result pushes the feeder one size larger. Keep the performance reason in the worksheet so the field crew does not downsize it later.
Aluminum branch circuit review
A planning result using aluminum conductors still needs terminal material, lug listing, oxide inhibitor requirements where specified, and torque instructions checked before the conductor choice is released.
Related calculators
Wire Size Calculator
Calculate NEC-style wire sizes from load current, ampacity basis, and voltage-drop targets
Wire Ampacity Calculator
Calculate conductor ampacity with temperature correction, conductor-count adjustment, and 60°C or 75°C termination checks
Circuit Breaker Sizing Calculator
Calculate standard breaker sizes for general loads, continuous loads, and simplified motor branch-circuit reviews
Voltage Drop Calculator
Calculate voltage drop in electrical conductors for single and three-phase systems
Related charts
Ampacity Chart
Review conductor ampacity as a heat problem: material, insulation, terminal rating, ambient correction, bundling adjustment, and equipment limits.
Voltage Drop Chart
Use this voltage drop chart: 3% equals 3.6 V at 120 V, 7.2 V at 240 V, and 14.4 V at 480 V; 5% equals 6 V, 12 V, and 24 V.
AWG to mm2 Chart
Convert American Wire Gauge sizes to approximate square millimeter conductor area for drawings, submittals, and procurement cross-checks.
Frequently asked questions
These answers explain how to use the chart without turning a quick reference into a final design decision.