NEC Voltage Drop Standards
Complete reference guide to National Electrical Code voltage drop requirements, recommendations, and compliance strategies for electrical professionals.
Maximum recommended voltage drop for branch circuits from the panel to the farthest outlet.
Maximum recommended voltage drop for feeders from the service entrance to the distribution panel.
Combined maximum voltage drop from service entrance to the farthest outlet (feeder + branch).
NEC Code References
NEC 210.19(A) — Branch Circuit Conductors
Informational Note No. 4
"Conductors for branch circuits as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation."
Note: This is an informational note, not a mandatory requirement. However, it represents industry best practice and is often required by specifications.
NEC 215.2(A) — Feeder Conductors
Informational Note No. 2
"Conductors for feeders as defined in Article 100, sized to prevent a voltage drop exceeding 3 percent at the farthest outlet of power, heating, and lighting loads, or combinations of such loads, and where the maximum total voltage drop on both feeders and branch circuits to the farthest outlet does not exceed 5 percent, provide reasonable efficiency of operation."
NEC 647.4(D) — Sensitive Electronic Equipment
Technical Power Systems
"The voltage drop on any branch circuit shall not exceed 1.5 percent. The combined voltage drop of feeder and branch-circuit conductors shall not exceed 2.5 percent."
This section applies specifically to technical power systems for sensitive electronic equipment, such as audio/video production facilities.
Voltage Drop Budget Allocation
The 5% total voltage drop limit should be allocated between feeder and branch circuits based on project requirements. Common allocation strategies include:
| Application | Feeder | Branch | Total |
|---|---|---|---|
| Standard Commercial | 2% | 3% | 5% |
| Long Branch Circuits | 1% | 4% | 5% |
| Long Feeders | 3% | 2% | 5% |
| Data Centers | 1% | 1% | 2% |
| Sensitive Electronics | 1% | 1.5% | 2.5% |
NEC Chapter 9 Reference Tables
Table 8 — DC Resistance
Conductor properties at 75°C for voltage drop calculations. Provides resistance values in ohms per 1000 feet for copper and aluminum conductors.
| Size | Cu (Ω/kft) | Al (Ω/kft) |
|---|---|---|
| 14 AWG | 3.14 | — |
| 12 AWG | 1.98 | — |
| 10 AWG | 1.24 | 2.04 |
| 8 AWG | 0.778 | 1.28 |
| 6 AWG | 0.491 | 0.808 |
| 4 AWG | 0.308 | 0.508 |
| 2 AWG | 0.194 | 0.319 |
| 1/0 AWG | 0.122 | 0.201 |
Table 9 — AC Impedance
Effective Z at 0.85 PF for AC circuits in different conduit types. Accounts for skin effect and proximity effect at 60 Hz.
| Size | Steel | PVC |
|---|---|---|
| 14 AWG | 3.1 | 3.1 |
| 12 AWG | 2.0 | 2.0 |
| 10 AWG | 1.2 | 1.2 |
| 8 AWG | 0.78 | 0.78 |
| 6 AWG | 0.52 | 0.49 |
| 4 AWG | 0.36 | 0.31 |
| 2 AWG | 0.26 | 0.20 |
| 1/0 AWG | 0.19 | 0.13 |
Compliance Checklist
- Calculate voltage drop for all circuits
Document voltage drop calculations as part of the electrical design package, especially for circuits over 50 feet.
- Verify branch circuit drops do not exceed 3%
From the panel to the farthest outlet on each branch circuit.
- Verify feeder drops do not exceed 3%
From the service entrance to each distribution panel.
- Verify total drop does not exceed 5%
Combined feeder and branch circuit drop from service to farthest outlet.
- Apply stricter limits where required
Check project specifications and AHJ requirements for stricter limits.
- Consider motor starting voltage drop
Evaluate temporary voltage drop during motor starting for circuits serving motors.
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