30 amp copper run at 60 feet
Learn about the 3% NEC informational note regarding voltage drop for 240V copper branch circuits at 30A over 60 ft. Understand derating exclusions and compliance.
Formula SSC-2026.1
K method · SSC-2026.1
Minimum size
10 AWG · 5.26 mm²
Single conductor set
Voltage drop
4.47 V
1.86% · end 235.5 V
Power loss
134 W
I²R at the operating current
Required ampacity
30.0 A
Each conductor 30 A
Material estimate
$259.20
3 conductors + EMT
Conductor weight
6.7 lb
3.0 kg · approximate insulated weight
Circle diameters track circular mils. The drawing is a schematic, not a conduit-fill layout.
| Item | Net | Waste | Order | Unit price | Line total | Source Spec Material / Tool |
|---|---|---|---|---|---|---|
| copper 10 AWG · 5.26 mm² | 60 ft one way | cuts excluded | 3 conductors | USD | $148.20 | Source Spec Material / Tool |
| EMT conduit | 60 ft | — | 60 ft | USD | $111.00 | Source Spec Material / Tool |
| 30 A breaker | 2-pole | — | 1 | Match the calculated load | — | Source Spec Material / Tool |
Source links open a product search on the Amazon storefront for the selected currency. SiteSpecCalc may earn a commission. The link does not change the quantities above.
| Material | Minimum size | mm² | Drop | End voltage | Loss |
|---|---|---|---|---|---|
| copper | 10 AWG · 5.26 mm² | 5.3 | 1.86% | 235.5 V | 134 W |
| aluminum | 8 AWG · 8.37 mm² | 8.4 | 1.93% | 235.4 V | 139 W |
| Distance | Minimum size | Drop | Percent | End voltage |
|---|---|---|---|---|
| 60 ft | 10 AWG · 5.26 mm² | 4.47 V | 1.86% | 235.5 V |
| 85 ft | 10 AWG · 5.26 mm² | 6.34 V | 2.64% | 233.7 V |
Show the deterministic formula
Single phase: Vdrop = 2 × K × I × D / cmil. Three phase: Vdrop = 1.732 × K × I × D / cmil. K is 12.9 for copper and 21.2 for aluminum. D is one-way feet.
Percent drop = Vdrop ÷ source voltage × 100. Green is 3% or less, amber is 3 to 5%, and red is over 5%. Power loss is I²R on the current-carrying conductors.
The smallest conductor that meets both the ampacity (125% when continuous) and the drop limit is selected. Ampacity does not include bundling or temperature correction.
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Project: 30 amp copper run at 60 feet
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This sheet is an estimate for ordering and layout discussion. It is not a sealed design. Confirm the quantities with a licensed local professional and the authority having jurisdiction before you buy or build.
Engineering notes
The National Electrical Code (NEC) provides guidelines to ensure safe and efficient electrical installations. One key aspect is the voltage drop in branch circuits. For a 240V copper branch circuit carrying 30A over a distance of 60 feet, the NEC recommends that the voltage drop should not exceed 3% of the supply voltage. This translates to a maximum allowable drop of 7.2 volts, ensuring that the equipment receives sufficient voltage for optimal performance.
It's important to note that derating factors, which may apply in certain conditions, are excluded from this calculation. This means that the 3% guideline stands independently, focusing solely on the voltage drop due to distance and load without additional adjustments for temperature or other environmental factors.
Code reference
Refer to NEC Article 210 for branch circuits and NEC Article 310 for conductors.
Field questions
- What is the significance of the 3% voltage drop guideline?
- The 3% voltage drop guideline helps ensure that electrical equipment operates efficiently and safely, preventing performance issues due to insufficient voltage.
- Are there any exceptions to the 3% rule?
- While the 3% guideline is a standard recommendation, specific applications may have different requirements. Always consult local codes and regulations.
- What does it mean that derating is excluded?
- Excluding derating means that the 3% voltage drop calculation is based solely on the distance and load without considering additional factors like temperature or conductor bundling.
- How do I calculate the voltage drop for my circuit?
- To calculate voltage drop, you can use the formula: Voltage Drop (V) = 2 × Length (ft) × Current (A) × Resistance (Ω/ft). For copper conductors, refer to NEC tables for resistance values.