Do I calculate voltage drop at 100% or 125% for a continuous load?

Use the design current that the circuit is expected to carry. For many NEC continuous-load branch circuits, that means 125% sizing under NEC 210.20(A) and 215.3, so a 32A continuous EV load is commonly checked as a 40A circuit while voltage drop is evaluated against the real sustained current and feeder budget.

Is an EV charger a continuous load under the NEC?

Yes. NEC 625 treats EV charging loads as continuous for branch-circuit and feeder sizing. A 32A Level 2 EVSE normally needs a 40A circuit, and a 48A EVSE normally needs a 60A circuit before voltage drop is checked.

What voltage-drop target should I use for continuous lighting?

A common design target is 3% on the branch circuit and 5% total feeder plus branch, matching NEC 210.19(A)(1) and NEC 215.2(A)(1) informational guidance. Long LED rows often perform better when the branch stays closer to 2% to 3%.

Does 125% continuous-load sizing automatically solve voltage drop?

No. The 125% factor helps conductor and overcurrent sizing for sustained heat, but distance still creates resistance. A 60A EV circuit at 48A over 180 ft can still need larger copper or aluminum conductors for performance.

How does IEC 60364 handle continuous-load voltage drop?

IEC 60364-5-52 coordinates design current, installation method, grouping, ambient correction, conductor size, and allowable voltage drop. The terminology differs from NEC, but the practical sequence is the same: thermal legality first, voltage performance second.

When should I upsize wire beyond the continuous-load minimum?

Upsize when the route is long, source voltage is weak, the equipment runs for 3 hours or more, or the feeder has already used 2% or more of the total voltage-drop budget. Compare at least two conductor sizes before releasing material.

连续负载电压降：125%电流、线径与NEC/IEC设计

连续负载不会像普通插座负载那样很快降下来。48 A电动车充电器、18 A商业照明回路或36 A工艺加热器会连续运行数小时，因此导线温升和电压降都必须按真实运行状态检查。

摘要

3 hours or more makes the load continuous in NEC practice.
125% sizing and voltage-drop calculation answer different questions.
Use branch, feeder, and total voltage-drop budgets together.
EVSE, lighting, heaters, and ventilation loads need sustained-current checks.

连续负载是指最大电流预计持续3小时或更久的负载。电压降是电流通过导体阻抗后在负载端损失的电压。载流量是导体在规定条件下不超过温度额定值可承载的电流。

先按NEC 210.20(A)、215.3、625或设备规则确定125%连续负载尺寸，再按实际持续电流、单程长度、铜/铝导体和馈线余量计算电压降。 NEC and IEC references keep the thermal and performance checks separate.

The 125% continuous-load rule is a heat and protection rule; it does not erase the resistance of a 150-foot branch circuit.
— Hommer Zhao, Technical Director

Continuous-load design checks

例如48 A、240 V EVSE通常按60 A回路设计。若6 AWG铜线单程165 ft，支路压降约6.3 V，即2.6%；若上游馈线已损失1.8%，总压降接近4.4%。

Load	Sustained current	NEC basis	Route	Design action
Level 2 EVSE	32 A at 240 V	40 A circuit	130 ft	Compare 6 AWG Cu
High-output EVSE	48 A at 240 V	60 A circuit	165 ft	Check feeder plus branch
LED lighting row	18 A at 277 V	125% review	240 ft	Split row or upsize
Process heater	36 A at 208 V	45 A design current	110 ft	Check 6 AWG and source
Exterior lighting	12 A at 120 V	15 A basis	95 ft	Use 10 AWG or split

For a 48-amp EV charger, document the 60-amp circuit sizing and check voltage drop at the sustained charging current.
— Hommer Zhao, Technical Director

Practical warning

125%规则解决的是持续发热和保护配合，不会消除150 ft导线的电阻。长距离连续负载仍可能需要加大一号线径。

Use the wire size calculator, the NEC requirements article, and the voltage drop vs ampacity guide together before material is released.

Continuous loads turn small voltage-drop misses into daily operating losses because the circuit stays loaded for hours.
— Hommer Zhao, Technical Director

FAQ

连续负载电压降按100%还是125%算？

电压降应按设备实际持续电流核算；NEC尺寸可能按125%选断路器和导线。例如32 A EVSE通常配40 A回路。

EV充电器属于连续负载吗？

是。NEC 625把EVSE视为连续负载，48 A充电器通常需要60 A回路。

连续照明建议多少压降？

常用目标是支路3%、馈线加支路总计5%；长LED线路最好控制在2%到3%。

什么时候需要加大线径？

当路线长、馈线已损失约2%、设备运行超过3小时或电源电压偏低时，应比较更大线径。

IEC项目怎么处理？

IEC 60364-5-52同时考虑设计电流、敷设方式、成组、环境温度和允许电压降。

拉线前，用计算器比较连续负载的规范下限线径和上一级线径。

Voltage Drop Calculator Contact

连续负载电压降：125%电流、线径与NEC/IEC设计

摘要

Continuous-load design checks

Practical warning

FAQ

连续负载电压降按100%还是125%算？

EV充电器属于连续负载吗？

连续照明建议多少压降？

什么时候需要加大线径？

IEC项目怎么处理？

开始计算

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