停车场照明压降与灯杆回路选型. 用 NEC 分支回路规则、IEC 电缆选型、沟槽路径示例和实际线径决策规划 277V、240V 与 480V 停车场照明。

Use this localized engineering guide with the same sequence: calculate the farthest pole voltage, compare branch and total drop, then verify NEC or IEC wiring, grounding, burial, and luminaire-driver requirements before trenching.

摘要

Calculate from the panel or lighting contactor to the farthest energized pole, not only from pole to pole.
A 277V lighting branch circuit can usually tolerate longer routes than 120V because the same watts draw less current.
NEC 210.19(A) and 215.2(A) notes commonly drive 3% branch and 5% total design targets.
IEC projects often coordinate IEC 60364-5-52 voltage-drop practice with luminaire driver input limits.

Definitions for Site-Lighting Circuits

Parking lot lighting is a fixed outdoor lighting system serving pole-mounted, wall-mounted, or canopy luminaires across a paved site.

Voltage drop is the conductor voltage loss between the source and the farthest operating luminaire caused by load current and conductor impedance.

A lighting contactor is a switching device that lets a photocell, time clock, or control relay energize multiple lighting circuits.

A multiwire lighting circuit is a branch-circuit arrangement where shared neutrals or multiple phases may reduce conductor count but require careful disconnecting and load-balance checks.

Design Workflow Before Trenching

Step 1

List the luminaire watts and driver input voltage. Twelve 110W LED heads at 277V draw about 4.8A before driver losses, while the same wattage at 120V draws about 11A.

Step 2

Draw the real route from panel to contactor, handhole, first pole, each intermediate pole, and the farthest pole. Include vertical risers and detours around drainage, landscaping, and future pavement cuts.

Step 3

Decide whether the circuit is a single long daisy chain, a center-fed branch, two shorter branches, or a 480V feeder with local 277V branch circuits.

Step 4

Run voltage drop at the real connected load and again at a reasonable future load if spare pole bases or higher-output heads are expected.

Step 5

After the voltage-drop pass, verify ampacity, conduit fill, burial depth, equipment grounding conductor sizing, wet-location insulation, and listed driver voltage range.

NEC and IEC Checkpoints

This guide uses public background on the National Electrical Code and the International Electrotechnical Commission while leaving final acceptance to the AHJ, adopted code edition, and project specification.

NEC 210.19(A) Informational Note No. 4 and 215.2(A) Informational Note No. 2 are commonly used for 3% branch-circuit and 5% combined feeder-plus-branch voltage-drop targets.
NEC 300.5, 300.9, and 310.10 are often relevant for underground wet-location raceways and conductor insulation on site-lighting work.
NEC 250.122 equipment grounding conductor sizing still follows the overcurrent device; upsizing ungrounded conductors for voltage drop may require checking 250.122(B).
NEC 410 and 110.3(B) keep luminaire listings, driver voltage range, pole wiring, and manufacturer instructions in the design review.
IEC 60364-5-52 provides voltage-drop and cable-sizing context for many IEC-based projects, while local national rules set the enforceable limits.

Parking Lot Lighting Layout Comparisons

These examples are planning checks for copper conductors at typical site-lighting currents. Use the calculator with your exact voltage, phase, route length, material, and power factor before issuing drawings.

Layout	Trial conductor	Voltage-drop result	Design decision
277V branch, 12 LED poles, 110W each, 420 ft one-way	10 AWG copper	About 2.6% at 4.8A	Usually workable; verify total feeder drop and driver input range
120V small lot, 8 LED poles, 80W each, 310 ft one-way	10 AWG copper	About 4.0% at 5.3A	Use 8 AWG, split the circuit, or move the contactor closer
480V feeder to remote lighting panel, 18A, 650 ft	4 AWG aluminum	About 3.2% three-phase	Check 2 AWG aluminum or a closer panel if branch circuits add more drop
240V single-phase pole circuit, 10A, 500 ft	6 AWG copper	About 2.6%	Good voltage-drop result; burial, splice, and handhole details may control
400V IEC car-park lighting, 9A, 180 m	10 mm2 copper	Often near a 3% target depending on method and PF	Coordinate IEC 60364-5-52, grouping, temperature, and luminaire range
Center-fed 277V branch, two 230 ft legs, 9A total	10 AWG copper	Lower drop than one 460 ft daisy chain	Center feeding can save copper and improve far-pole voltage

Worked Calculator Examples

277V LED pole circuit: 12 heads, 110W each, 420 ft

Total load is 1,320W. At 277V, current is about 4.8A. Enter 277V, single-phase AC, copper, 4.8A, and 420 ft. 10 AWG copper can land near 2.6% drop, so it may meet a 3% branch-circuit target if the upstream feeder drop is controlled.

120V retrofit lot: 8 heads, 80W each, 310 ft

The same site at 120V draws about 5.3A for 640W. With 10 AWG copper over 310 ft, voltage drop can approach 4%. Moving to 8 AWG or splitting the branch into two 155 ft legs can bring the farthest driver closer to the common 3% target.

480V feeder to a remote lighting panel: 18A, 650 ft

For a three-phase 480V feeder at 18A and 650 ft, 4 AWG aluminum may calculate around 3.2% before any branch-circuit drop. If the project specification limits total drop to 5%, the branch circuits from the remote panel may leave too little margin unless the feeder is upsized or shortened.

Field Checklist Before You Release the Plan

Use one-way route length from source to farthest energized pole, including risers and handholes.
Use connected luminaire watts and driver input current; do not size voltage drop from breaker rating alone.
Check feeder and branch drop together if a remote lighting panel or contactor cabinet is used.
Confirm wet-location conductor insulation, burial depth, conduit fill, handhole space, and listed splice kits.
Check NEC 250.122(B) when ungrounded conductors are upsized for voltage drop.
For IEC work, document cable installation method, grouping, ambient temperature, protective device, and luminaire input range.

Common Questions

What voltage-drop limit should I use for parking lot lighting?

Many NEC-based designs use 3% for the branch circuit and 5% total feeder-plus-branch from NEC 210.19(A) and 215.2(A) informational notes. Project specifications can be stricter.

Should I calculate from the contactor or from the main panel?

Calculate both when the contactor is remote. The branch-circuit drop starts at the contactor output, but the total operating voltage at the pole includes the feeder drop supplying that contactor.

Why does 277V help long lighting circuits?

For the same watts, 277V draws less than half the current of 120V. Lower current reduces voltage drop and conductor heating on long pole-lighting routes.

Can I use breaker size instead of actual lighting load?

Use actual connected load for voltage drop, then verify breaker, conductor ampacity, continuous-load sizing, and future spare capacity separately. A 20A breaker does not mean the circuit actually draws 20A.

Does upsizing phase conductors require a larger equipment grounding conductor?

Often it must be checked. NEC 250.122(B) requires proportional upsizing of the equipment grounding conductor when ungrounded conductors are increased in size for reasons such as voltage drop.

How do IEC projects handle site-lighting voltage drop?

IEC-based projects commonly use IEC 60364-5-52 cable-sizing and voltage-drop guidance, then apply national rules, installation method corrections, protective-device coordination, and luminaire manufacturer voltage limits.

Check the Far Pole Before the Trench Is Dug

Compare 120V, 240V, 277V, 400V, and 480V layouts with the real pole count, route length, conductor material, and load current while the panel or contactor location can still move.

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停车场照明压降与灯杆回路选型

摘要