1. Definition & Physical Basis Allowable voltage drop is the maximum permissible reduction in voltage between the source (e.g., transformer, generator, utility service point) and the load (e.g., motor, lighting, control panel) under steady-state operating conditions.
| Standard / Body | System Type | Allowable Drop | Notes | |----------------|-------------|----------------|-------| | – 215.2(A)(1)(b) & 210.19(A)(1) Informational Note | Branch circuits + Feeders | 3% branch circuit 5% total (feeder + branch) | Not mandatory but enforceable via “good engineering practice” | | IEC 60364-5-52 | Low-voltage installations | 4% for lighting 6% for other uses (motors, heat) | Measured from supply origin to load | | BS 7671 (UK) | LV installations | 3% lighting 5% power | Similar to IEC | | IEEE Std 141 (Red Book) | Industrial plants | 2–5% for feeders 2–4% for branch circuits | More stringent for sensitive equipment | | CENELEC HD 60364 | European LV | 4% lighting / 8% others | For public distribution | | AS/NZS 3000 | Australia / NZ | 5% total | Includes voltage drop in final subcircuits | allowable voltage drop
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