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Drop {{ values ? formatPercent(values.recommended_drop_percent) : '—' }} Ampacity screen {{ values ? formatAmps(values.recommended_screen_ampacity_a) : '—' }} Material {{ values ? materialLabel : '—' }}
Source {{ formattedInputLength }} Load {{ formattedLoadCurrent }}
Choose the electrical path used for the voltage-drop estimate.
Operating current from 0.01 A through 600 A.
A
Changing units converts the displayed value without changing the physical run.
Nominal voltage from 1 V through 1,000 V.
V
Planning limit from 0.1% through 20%.
%
Actual conductor construction and alloy can change resistance and permitted use.
A conservative planning link between conductor resistance temperature and the reference ampacity column.
Use 100% for no added margin. Apply required load rules separately and deliberately.
%
The default follows the current recommendation.
Two decimal places is the neutral default.
Sizing decision
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Why this gauge:
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The chart renderer is unavailable. The same candidate data remains available in the ledger.

Gauge Drop Ampacity screen Status Copy
{{ row.gauge }} {{ row.drop }} {{ row.ampacity }} {{ row.status }}
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Wire size has to satisfy two different questions. Will the conductor carry the design current under the assumed installation conditions, and will its resistance keep voltage drop within the chosen limit? Passing only one check is not enough.

American Wire Gauge (AWG) numbers run opposite to conductor size: a smaller gauge number means a larger diameter. After 1 AWG, the sequence continues through 1/0, 2/0, 3/0, and 4/0. A larger conductor has lower resistance, so it loses less voltage over the same current and distance, but it also costs more and can be harder to terminate.

CheckMain inputsWhat a failure means
Voltage dropLoad current, one-way length, system voltage, circuit path, material, and conductor temperatureThe load may receive less voltage than the planning limit allows.
Ampacity screenLoad current, sizing margin, material, and 60/75/90 °C reference columnThe design current is above the stored reference value.

The circuit path changes the resistance length. DC and single-phase two-wire circuits use the outgoing-and-return path, twice the one-way length. A balanced three-phase estimate uses a √3 multiplier. Entering the round-trip distance as the one-way run would therefore count the return path twice.

Ampacity depends on more than gauge. Insulation, terminal ratings, ambient temperature, conductor count, bundling, raceway or cable type, load duty, overcurrent protection, and local code can change the permitted size. The 60/75/90 °C choice is only a reference column here; it does not decide which column an actual installation is allowed to use.

Use the result as a screening calculation, then verify the complete circuit with current adopted rules, equipment instructions, and a qualified electrical professional. Voltage-drop preferences do not override minimum conductor, protection, or termination requirements.

How to Use This Tool:

Choose the circuit model and one-way run first, then test conductor sizes against both voltage drop and ampacity.

  1. Choose DC/two-wire, single-phase AC, or balanced three-phase AC, then enter operating current and the physical one-way run length.
  2. Enter nominal system voltage and the maximum acceptable voltage-drop percentage. Lower-voltage and longer circuits usually need larger conductors for the same power.
  3. Choose copper or the aluminum EC-H19 estimate and select the ampacity reference column only after checking conductor insulation and terminal limitations.
  4. Set the Ampacity sizing margin. A value of 100% adds no margin; enter a larger value only to represent a deliberately chosen design-current factor.
  5. Review the recommended gauge and candidate ledger. Confirm that both the drop and ampacity checks pass, then apply all installation-specific adjustment, protection, and code rules separately.

Interpreting Results:

The recommendation is the first supported AWG size, from 18 AWG through 4/0, that passes both checks. Voltage-drop fail means the calculated percentage is above the selected limit. Ampacity-screen fail means design current is above the stored screened value. A row with no building-wire ampacity reference cannot be recommended even if its voltage drop passes.

Treat a pass as permission to continue the design review, not permission to install. Verify the conductor product, terminal temperature rating, current-carrying conductor count, ambient correction, load rules, fault protection, and adopted electrical code before selecting equipment or cable.

Technical Details:

Voltage drop follows Ohm's law using a temperature-adjusted conductor resistance. Copper starts from stored AWG resistance values at 20 °C; aluminum resistance is derived from EC-H19 resistivity and AWG cross-sectional area.

Formula Core:

d=0.127×9236−n39 A=π(d2)2 RT=R20[1+α(T−20)]

The temperature coefficient α is 0.00393/°C for copper and 0.00403/°C for aluminum. Aluminum uses a resistivity of 0.028264 Ω·mm²/m at 20 °C.

Vdrop=I×RT×L×k Droppercent=100×VdropVsystem

The path multiplier k is 2 for DC/two-wire and single-phase circuits, or √3 for balanced three-phase. Design current equals load current × sizing margin ÷ 100. Full precision determines pass or fail; the display precision changes formatting only.

Lookup Core:

The ampacity screen uses the following stored 60/75/90 °C values. A dash means no reference value is available for that material and size.

AWGCopper, AAluminum, A
60 °C75 °C90 °C60 °C75 °C90 °C
14152025———
12202530152025
10303540253035
8405055354045
6556575405055
4708595556575
385100115657585
2951151307590100
111013015085100115
1/0125150170100120135
2/0145175195115135150
3/0165200225130155175
4/0195230260150180205

Rule Core:

  • A candidate passes voltage drop when calculated drop ≤ the selected maximum.
  • A candidate passes ampacity when design current ≤ the screened ampacity value.
  • Small-conductor caps reduce copper 14/12/10 AWG to 15/20/30 A and aluminum 12/10 AWG to 15/25 A, regardless of the higher stored temperature-column entry.
  • The first candidate that passes both rules is recommended. If none passes through 4/0, no recommendation is returned.

Accuracy and Safety Notes:

This is a preliminary reference screen, not a code-compliance determination. The resistance model does not account for every conductor construction, strand lay, connection resistance, reactance, harmonic effect, or actual operating temperature. The ampacity lookup does not apply ambient or conductor-count corrections or verify terminal ratings.

Electrical installation and conductor selection can create fire, shock, and equipment risks. Verify the full design with the currently adopted code, product listings, manufacturer instructions, and a qualified electrician or engineer. Calculation stays in the browser and no entered circuit data is sent to a calculation service.

References: