Disclaimer: RacewayIQ is an informational engineering tool only. All calculations must be independently verified by the user. Do not rely on these results as the sole basis for design, procurement, installation, construction, permitting, or code compliance decisions.

Feeder Sizing Calculator

Check feeder ampacity, continuous-load sizing, parallel conductors, and voltage drop using selected conductor assumptions. This calculator checks a selected feeder; selected allowable ampacity must already include applicable derating, ambient correction, terminal temperature limits, and project requirements.

Job Information

Project nameLocationPrepared byDateNotes

Main Inputs

Feeder calculation modeThis calculator checks a selected feeder. Automatic feeder design requires verified conductor ampacity, derating, and voltage-drop data. Use Check selected feeder for now.Continuous load (A)Load expected to operate continuously where continuous-load sizing applies.Noncontinuous load (A)Load not treated as continuous for feeder ampacity sizing.Continuous-load factor

Default 1.25 represents 125% continuous-load sizing. Change only when project rules or load conditions require it.Selected final allowable ampacity per conductor (A)Enter the final allowable ampacity after applicable derating, ambient correction, terminal temperature limitation, and project requirements.Parallel conductors per phase or polarityEnter 1 for a single conductor set. Enter the number of parallel conductors per phase or polarity for larger feeders.Electrical system

Choose the system serving the load so the voltage-drop formula uses the right multiplier.Nominal system voltage (V)Use the nominal line voltage for the feeder, such as 120, 208, 240, or 480 V.Voltage drop current basisVoltage drop is typically checked using the load current expected to flow on the feeder. This may differ from the continuous-load ampacity sizing current.Conductor materialSelect the actual conductor material used for voltage-drop calculation.Conductor sizeChoose the proposed feeder conductor size for the voltage-drop check.One-way feeder length (ft)Use the routed one-way conductor length from source to load. Do not enter round-trip distance.Allowable voltage drop target (%)

Enter the project voltage drop target. Common feeder design targets are often 3% unless project criteria differ.

Advanced Inputs

Use these when the job has project-specific assumptions, manufacturer data, or review conditions.

Insulation typeDocumentation only unless verified automatic ampacity lookup is implemented.Terminal temperature ratingDocumentation only. Verify actual equipment termination temperature rating.Ambient correction factor, optional/manualDocumentation field for the factor already included in selected final allowable ampacity.Current-carrying conductor adjustment factor, optional/manualDocumentation field for the factor already included in selected final allowable ampacity.Voltage-drop reference editionThis changes the NEC reference edition shown for the voltage-drop portion of the report. It does not change feeder ampacity, derating, or voltage-drop math.Include grounding recommendationPreliminary EGC sizing is based on the feeder OCPD rating and must be verified separately.

Result

Review

Actual load current

100 A

Required feeder ampacity

120 A

Available ampacity

130 A

Ampacity utilization

92.3%

Voltage drop current used

100 A

Voltage drop

2.12 V / 0.44%

Voltage at load

477.88 V

Ampacity status

Review Required

Voltage drop status

Pass

Overall status

Review Required

Reason

Feeder ampacity passes, but utilization is above the review threshold. Verify selected allowable ampacity, spare capacity, terminal ratings, derating, and project requirements.

Practical Next Steps

Treat this as a workable planning result that still needs review.
Resolve warnings that are close to limits, based on manual assumptions, or missing manufacturer data.
Confirm the result against the project specification before procurement, permitting, or installation.

Selected final allowable ampacity must include all applicable derating, ambient correction, terminal temperature limits, and project requirements.

Conductor size and selected final allowable ampacity are independent inputs. Confirm they describe the same conductor and installation condition.

Feeder ampacity utilization is above the review threshold. Confirm spare capacity, load assumptions, terminal ratings, and project requirements.

Voltage drop was calculated using actual load current, not continuous-load sizing current. Verify this matches the project design basis.

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Calculation Breakdown

Load Summary

Continuous load: 80 A
Noncontinuous load: 20 A
Continuous-load factor: 1.25
Actual load current: 100 A
Required feeder ampacity: (80 A x 1.25) + 20 A = 120 A

Ampacity Check

Selected final allowable ampacity per conductor: 130 A
Parallel conductors per phase/polarity: 1
Available ampacity: 130 A x 1 = 130 A
Ampacity utilization: 92.3%
Ampacity result: Review Required

Voltage Drop Check

Electrical system: Three-phase AC
Nominal system voltage: 480 V
Voltage drop current basis: Actual load current
Voltage drop current used: 100 A
Conductor: 1/0 AWG Cu
One-way feeder length: 100 ft
Voltage drop: 2.12 V
Voltage drop percentage: 0.44%
Voltage at load: 477.88 V
Voltage drop result: Pass

Conductor Basis

Insulation type: THHN / THWN-2
Terminal temperature rating: 75 deg C
Ambient correction factor: 1.000
Current-carrying conductor adjustment factor: 1.000
Voltage-drop reference edition: 2023 NEC

Overall Result

Status: Review Required
Reason: Feeder ampacity passes, but utilization is above the review threshold. Verify selected allowable ampacity, spare capacity, terminal ratings, derating, and project requirements.

Code and Design References

Feeder Ampacity Coordination

Coordinate continuous and noncontinuous load sizing, selected conductor ampacity, derating, terminal limitations, and project requirements. The selected final allowable ampacity must already include applicable correction, adjustment, and terminal limitations.

Automatic feeder selection is not exposed until verified ampacity, conductor, derating, and voltage-drop data are implemented.

Voltage Drop Design Notes

Voltage drop is typically treated as a design criterion unless adopted by project specifications, owner requirements, or AHJ requirements.

Voltage drop current can differ from ampacity sizing current when continuous-load factors are applied.

Conductor Data

Voltage drop calculations depend on conductor material, conductor size, conductor properties, and selected calculation method. Verify conductor data against the adopted standard or manufacturer data.

Parallel Conductors

Parallel feeder installations require review of conductor size, grouping, raceway configuration, terminations, and applicable code requirements.

NEC 210.19(A) Informational Note

Branch-circuit voltage drop guidance is generally treated as a design recommendation rather than a mandatory rule unless adopted by project or AHJ requirements.

NEC 215.2(A)(1) Informational Note

Feeder voltage drop guidance should be coordinated with branch-circuit voltage drop and project performance requirements.

NEC Chapter 9, Table 8

Conductor properties for DC resistance and circular mil area. This app stores editable conductor data for update by edition and project standard.

NEC Chapter 9, Table 9

AC resistance and reactance data for conductors in raceways. Use impedance method where reliable R/X data applies.

IEEE 3002.2

Recommended practice for load-flow studies and analysis of industrial and commercial power systems.