Should voltage drop be calculated using breaker size or load current?

Use load current when the load is known, and use breaker size only when the circuit is intended to deliver that current. For a 12A dedicated load on a 20A breaker, 12A describes operation; for a general 20A receptacle, 16A continuous or 20A full-capacity checks may be better.

Do NEC voltage-drop notes require a 3% maximum?

NEC 210.19(A) and 215.2(A) voltage-drop language is commonly in informational notes, not a universal mandatory rule. The 3% branch or feeder and 5% combined targets are still widely used for efficient design and plan documentation.

What current should I use for a 32A EV charger?

For a 32A continuous EVSE on a 40A branch circuit, calculate voltage drop at 32A for expected charging operation and at 40A for the 125% continuous-load design basis under NEC EVSE and branch-circuit sizing rules.

For motors, should I use FLA, MCA, or breaker size?

Use the equipment nameplate, MCA, or NEC Article 430 table current for conductor and operating voltage-drop checks. Do not use a 60A motor breaker as the running current unless the motor load can actually draw 60A continuously.

How does IEC 60364 handle this differently?

IEC 60364 design normally separates design current Ib, protective-device current In, and cable capacity Iz. Voltage drop is usually checked from Ib, while In and Iz are used to verify protection and cable coordination.

Should I calculate at 80% of breaker size for continuous loads?

For many NEC circuits, continuous load is limited to 80% of a standard breaker unless equipment is rated otherwise, which is equivalent to sizing at 125%. A 20A circuit often supports 16A continuous load, and a 40A circuit often supports 32A EVSE load.

전압 강하는 설계 부하인가 차단기 용량인가: NEC와 IEC 예제

차단기 정격은 운전 전류가 아닙니다. 전압 강하 계산은 먼저 실제로 흐를 전류를 정하는 일에서 시작합니다.

요약

설계 부하는 명판, 연속 부하 규정, MCA 또는 부하 계산으로 정한 전류입니다. 차단기는 도체 보호를 위한 정격입니다.
120 V, 115 ft, 12 AWG 동선, 12 A 충전기는 약 4.38 V, 3.65%가 떨어집니다. 16 A 연속 부하로 보면 약 4.87%입니다.
모터와 HVAC는 60 A MOCP가 아니라 MCA, NEC 430/440, 명판 전류를 기준으로 정상 운전 전압 강하를 봅니다.
IEC 60364-5-52는 Ib, In, Iz를 나누어 검토하며, 전압 강하는 보통 설계 전류 Ib에서 시작합니다.

NEC and IEC references are useful only when the current basis is written clearly beside the calculation.