Allowable Voltage Drop -

“All branch circuit voltage drop shall not exceed 3% from final overcurrent device to load. Total voltage drop from service entrance to furthest load shall not exceed 5% under steady-state full load conditions, calculated at 75°C conductor temperature and with load power factor as specified. For LED lighting and electronic loads, total drop shall not exceed 3%.”

[ V_d = \sqrt3 \times I \times (R\cos\theta + X\sin\theta) \times L ] Where:

Specific resistance of the material (approx. 12.9 for copper). I: Current in Amperes. allowable voltage drop

| Load Type | Recommended Total Drop | Reasoning | |-----------|------------------------|------------| | Incandescent lighting | 3% | Visible flicker at 4% | | LED lighting | 3% | Driver input range | | Induction motor (continuous) | 4% | Starting torque margin | | Induction motor (intermittent) | 5% | Acceptable if start infrequent | | Resistance heating | 8% | Power drops as (V^2), but acceptable for non-critical | | Data center IT load | 2–3% | PSU hold-up time and efficiency | | Residential general use | 5% | NEC Informational Note | | Heavy industrial (welding, cranes) | 10–12% | By special allowance, with larger contactors |

This post breaks down what "allowable voltage drop" means, the standards that define it, and how to ensure your installations stay within safe limits. “All branch circuit voltage drop shall not exceed

The more current flowing through the wire, the higher the voltage drop.

The longer the wire, the more resistance it has. The more current flowing through the wire, the

The voltage drop can be calculated using the following formula:

[ V_d = \sqrt3 \times K \times I \times L \times \textmultiplier / \textcmil ] Multiplier: 1.0 for copper, 1.28 for aluminum (approximate).