Voltage Drop Calculator
Calculate wire size for long electrical runs
Circuit Parameters
Use RLA or full load amps from nameplate
Distance from panel to equipment
Results
Voltage Drop
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Voltage at Load
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Status
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Recommended Wire Size
For 3% drop:
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For 5% drop:
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Wire resistance:
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Power loss:
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Copper Wire Resistance (ohms/1000ft @ 75°C)
| AWG | mm² | Ω/1000ft | Ampacity |
|---|---|---|---|
| 14 | 2.5 | 3.14 | 15A |
| 12 | 4 | 1.98 | 20A |
| 10 | 6 | 1.24 | 30A |
| 8 | 10 | 0.778 | 40A |
| 6 | 16 | 0.491 | 55A |
| 4 | 25 | 0.308 | 70A |
| 2 | 35 | 0.194 | 95A |
| 1/0 | 55 | 0.122 | 125A |
NEC Voltage Drop Guidelines
3% Recommendation (NEC 210.19(A))
Branch circuits should have voltage drop ≤3% for satisfactory equipment operation.
5% Maximum (NEC 215.2(A)(1))
Combined feeder and branch circuit voltage drop should not exceed 5%.
Motor Applications
Motors are sensitive to voltage. Most require ±10% of nameplate voltage. Lower voltage = higher current = overheating.
Important Notes
- • This calculator assumes resistive load. Motor loads may require additional considerations for power factor.
- • Always verify wire size meets minimum ampacity requirements (NEC Table 310.16).
- • Temperature derating may be required for high ambient or bundled conductors.
- • Consult local electrical codes - they may have additional requirements.
- • For HVAC equipment, also check MCA (Minimum Circuit Ampacity) on nameplate.