Parking Lot Lighting Wire Sizing Service Guide
// A PRACTICAL WORKFLOW FOR SIZING OUTDOOR POLE-LIGHT CIRCUITS, SIGN CIRCUITS, TRENCH RUNS, AND REMOTE LIGHTING PANELS BEFORE INSTALLATION. //
Parking lot lighting is a long-run outdoor wiring problem before it is a simple fixture schedule. LED poles, signs, contactors, time clocks, photocells, underground raceways, and remote panels all affect conductor size. Start with real fixture watts, voltage, phase, one-way distance, continuous-load treatment, wet-location conductors, grounding, and voltage-drop target before selecting AWG or IEC cable size.
Continuous lighting load
If lights run 3 hours or more, NEC 210.19(A)(1), 210.20(A), 215.2(A)(1), and 215.3 commonly push conductor and protection checks to 125%.
Voltage drop target
Use 3% branch-circuit and 5% feeder-plus-branch as common NEC design targets, then tighten the target when LED drivers or owner specs require it.
IEC cross-check
IEC 60364-5-52 checks current-carrying capacity, installation method, grouping, ambient temperature, and Clause 525 voltage drop for outdoor cable runs.
Sizing workflow
1. Build the lighting schedule
Record fixture watts, sign loads, pole count, voltage, phase, control gear, spare poles, and the farthest one-way distance from the source.
2. Convert watts to design current
Divide watts by volts and phase as applicable, then apply 125% when the lighting load is continuous or the feeder carries continuous lighting for 3 hours or more.
3. Choose conductor basis
Use NEC 310 ampacity tables with terminal temperature and correction factors, or IEC 60364-5-52 tables for the installation method and cable grouping.
4. Check voltage drop
Run each branch or feeder in the calculator with one-way distance, material, current, voltage, and phase. Long 277V and 120V lighting runs often upsize for voltage drop before ampacity fails.
5. Coordinate the outdoor details
Verify burial depth, wet-location insulation, pole handholes, equipment grounding conductor, disconnecting means, contactor rating, surge protection, and AHJ requirements.
Worked examples
277V LED pole circuit
Twelve 150W luminaires on one 277V branch, 260 ft one-way copper run, lights operate dusk to dawn.
1800W / 277V = 6.5A, then 6.5A x 125% = 8.1A. #12 AWG may pass ampacity, but #10 AWG is often reviewed to keep voltage drop near 3%.
120V sign and entry lighting
900W monument sign plus 600W entry lights, 180 ft one-way copper branch, 15A breaker, nightly operation.
1500W / 120V = 12.5A, continuous design current is 15.6A. A 20A circuit with #12 AWG may be needed for load, and #10 AWG may be selected for voltage drop.
400V IEC parking area feeder
32A three-phase lighting feeder, 70 m one-way, copper multicore cable in underground duct with grouped circuits.
6 mm2 may pass ampacity in some methods, but 10 mm2 can be reviewed when grouping and IEC 60364-5-52 Clause 525 voltage drop are included.
Outdoor lighting comparison
| Load | Sizing basis | Likely conductor check | Voltage-drop risk | Code note |
|---|---|---|---|---|
| 277V pole-light branch | Fixture watts plus 125% continuous check | #12 AWG Cu minimum check, #10 AWG on long runs | Medium beyond 200 ft | NEC 210.19(A)(1), 410, 310 |
| 120V sign circuit | Nameplate sign load plus lighting controls | #12 AWG Cu often starts the review | High because 3% is only 3.6V | NEC 600, 210, 225 |
| Remote lighting panel feeder | Calculated lighting and spare capacity | Feeder ampacity, neutral, EGC, and drop | High on large lots | NEC 215.2(A)(1), 220, 250 |
| Underground branch circuit | Wet-location conductors in raceway | THWN-2 or listed wet-location cable | Medium with long pole spacing | NEC 300, 310, 225 |
| 400V IEC lighting feeder | Design current and installation method | 6-10 mm2 depending method and drop | Medium on 50-90 m runs | IEC 60364-5-52, IEC 60228 |
Code checkpoints
Use these references as design checkpoints, then confirm the adopted edition, utility rules, and local amendments with the authority having jurisdiction.
NEC 210.19(A)(1) and 210.20(A)
Branch-circuit conductors and overcurrent devices are checked against the load, with continuous lighting commonly calculated at 125%.
NEC 215.2(A)(1) and 215.3
Feeders serving remote lighting panels need load, continuous-duty, and voltage-drop review before branch circuits are added.
NEC 225
Outside branch circuits and feeders bring routing, disconnecting, and building or structure supply rules into the design.
NEC 410 and 600
Luminaires and electric signs can have fixture, listing, support, and disconnect requirements beyond conductor ampacity.
NEC 300, 310, and 250
Underground raceways, wet-location insulation, conductor ampacity, correction factors, and grounding must be checked together.
IEC 60364-5-52 and IEC 60228
Use installation method, grouping, conductor class, cross-sectional area, and Clause 525 voltage-drop guidance.
Field checklist
- Measure the farthest one-way route after trench routing is known.
- Use actual LED driver watts or sign nameplate current, not only pole count.
- Treat dusk-to-dawn lighting as continuous unless the schedule proves otherwise.
- Check 120V circuits carefully because small voltage losses become large percentages.
- Confirm conductors are rated for wet locations inside underground raceway.
- Verify pole grounding, handhole splices, surge protection, and photocell or contactor ratings.
- Keep voltage-drop and ampacity calculations with the lighting schedule and as-built panel directory.
Parking lot lighting wire sizing FAQ
What wire size is used for 277V parking lot lights?
For twelve 150W luminaires at 277V, load is about 6.5A and the 125% continuous check is about 8.1A. #12 AWG copper may pass ampacity, while #10 AWG can be selected on a 260 ft run to control voltage drop.
Do parking lot lights count as continuous loads?
Usually yes. Dusk-to-dawn lighting often runs longer than 3 hours, so NEC 210.19(A)(1), 210.20(A), 215.2(A)(1), and 215.3 are commonly checked at 125%.
What voltage drop should I allow for LED pole lights?
A common NEC design target is 3% on the branch circuit and 5% total feeder plus branch. For a 120V circuit, 3% is only 3.6V, so long runs need careful review.
Can I size outdoor lighting from breaker size only?
No. Start with fixture watts, sign nameplate current, continuous-load math, conductor ampacity, and voltage drop. A 20A breaker does not automatically make #12 AWG acceptable for a 200 ft run.
Does underground raceway change the wire choice?
Yes. Raceways outdoors and underground are generally wet locations, so insulation such as THWN-2 or an approved wet-location cable must be verified along with burial depth and conduit fill.
How does IEC parking lot lighting sizing differ from AWG?
IEC projects use mm2 conductor sizes, installation methods, grouping factors, ambient correction, and IEC 60364-5-52 voltage-drop checks instead of AWG selection alone.
Screen the lighting schedule before trenching
Use the batch, voltage-drop, and ampacity tools to compare code-minimum conductors with the practical sizes that keep remote lights, signs, and controls stable at night.