Marina Shore Power Wire Sizing Service Guide
// A PRACTICAL WORKFLOW FOR SIZING DOCK FEEDERS, SHORE POWER PEDESTALS, BOAT SLIPS, AND WATERFRONT BRANCH CIRCUITS BEFORE CABLE IS PULLED. //
Marina shore power is a wet-location feeder and pedestal problem, not just a receptacle count. Shore power is the utility supply that lets a vessel connect to dock power while berthed. A marina pedestal is an outdoor power outlet assembly that may serve 30A, 50A, or larger boat loads. Voltage drop is the conductor voltage loss that grows with current and one-way dock distance. Start with slip count, pedestal ratings, demand assumptions, conductor material, raceway grouping, grounding, GFCI protection, and the farthest one-way run before choosing AWG or IEC cable size.
NEC marina scope
NEC Article 555 covers marinas, boatyards, floating buildings, docking facilities, and related shore power wiring, while 210, 215, 250, 300, and 310 still shape conductor sizing.
Voltage drop target
Use 3% branch-circuit and 5% feeder-plus-branch as common NEC design targets, then tighten the target for long piers or sensitive onboard chargers.
IEC marina cross-check
IEC 60364-7-709 covers marinas and similar locations, while IEC 60364-5-52 checks installation method, grouping, ampacity, and voltage drop.
Sizing workflow
1. Map the dock load
Record each slip, receptacle rating, voltage, phase, pedestal quantity, transformer or panel location, and the farthest one-way cable route along the dock.
2. Establish design current
Use nameplate pedestal ratings, NEC 220 demand logic where accepted, project load diversity, and owner requirements before assuming every receptacle is fully loaded at once.
3. Select conductor basis
Check NEC 310 ampacity with terminal temperature, wet-location insulation, ambient correction, and adjustment for grouped current-carrying conductors or use IEC 60364-5-52 tables for the installation method.
4. Run voltage drop
Enter design current, voltage, phase, conductor material, and one-way distance in the voltage-drop calculator. Long 120V dock branches often upsize before ampacity becomes the limiting factor.
5. Coordinate safety details
Confirm NEC 555 GFCI requirements, equipment grounding conductors, bonding, corrosion-resistant hardware, disconnects, pedestal listings, conduit fill, and AHJ marina rules before installation.
Worked examples
30A 120V slip branch
One 30A shore power receptacle, 180 ft one-way copper run from dock panel to pedestal, wet-location conductors in raceway.
#10 AWG copper may satisfy a 30A ampacity check, but voltage drop at 24A design current is often reviewed against the 3% target of 3.6V, so #8 AWG may be selected.
Two 50A 120/240V pedestals
Two slips with 50A 120/240V shore power, 140 ft one-way feeder, copper conductors, load diversity documented by the designer.
A 100A raw connected load may be reduced only when the adopted code and AHJ allow the demand method. Check #3 AWG or #2 AWG copper for ampacity, then compare voltage drop at the calculated feeder current.
400V IEC dock feeder
63A three-phase marina feeder, 85 m one-way, copper multicore cable in a dock raceway with other circuits.
16 mm2 may pass in some installation methods, but 25 mm2 can be reviewed when grouping factors and IEC 60364-7-709 service expectations are included.
Dock power comparison
| Load | Sizing basis | Likely conductor check | Voltage-drop risk | Code note |
|---|---|---|---|---|
| 30A 120V pedestal | Receptacle rating and design load | #10 AWG Cu starts the review, #8 AWG on long runs | High beyond about 150 ft | NEC 555, 210, 310 |
| 50A 120/240V pedestal | Two-pole shore power circuit | #6 AWG Cu starts the review, larger for distance | Medium on long fingers | NEC 555, 250, 406 |
| Dock feeder panel | Slip schedule and permitted demand | Feeder ampacity, neutral, EGC, and drop | High on long piers | NEC 215, 220, 555 |
| Floating dock section | Flexible routing and wet location | Listed cable or raceway conductors | Medium with movement and corrosion | NEC 300, 555 |
| 400V IEC marina feeder | Design current and installation method | 16-25 mm2 depending method and drop | Medium on 60-100 m runs | IEC 60364-7-709, IEC 60364-5-52 |
Code checkpoints
Use these references as design checkpoints, then confirm the adopted edition, marina owner standard, utility rules, and local AHJ amendments.
NEC Article 555
Applies marina-specific rules for shore power, docking facilities, floating structures, GFCI protection, wiring methods, and equipment in wet corrosive areas.
NEC 210 and 215
Branch circuits and feeders still need load, continuous-duty, overcurrent, conductor, and voltage-drop review before dock layout decisions are final.
NEC 220
Load calculation and demand assumptions must be documented before a feeder is reduced below the sum of pedestal ratings.
NEC 250
Equipment grounding, bonding, and fault-current path continuity are critical around water and metallic dock systems.
NEC 300 and 310
Wet-location wiring methods, raceway fill, conductor insulation, ampacity, correction factors, and adjustment factors shape the final conductor size.
IEC 60364-7-709 and 60364-5-52
Use marina-specific requirements with current-carrying capacity, installation method, grouping factors, conductor cross-sectional area, and voltage-drop checks.
Field checklist
- Measure the actual cable route along the dock, not the straight-line distance over water.
- Separate 120V branch voltage-drop checks from 120/240V feeder checks.
- Document demand assumptions before reducing a feeder serving multiple slips.
- Use conductors and equipment listed for wet, outdoor, corrosive marina conditions.
- Confirm GFCI protection thresholds and trip coordination with the adopted NEC edition and AHJ.
- Check equipment grounding conductor size, bonding jumpers, metal dock sections, and shore transformer grounding.
- Keep the voltage-drop worksheet with the panel schedule, pedestal schedule, and as-built dock drawings.
Marina shore power wire sizing FAQ
What wire size is used for a 30A marina pedestal?
#10 AWG copper is a common starting point for a 30A circuit, but a 180 ft 120V run at 24A design current may need #8 AWG to stay near a 3% voltage-drop target.
Can I size a marina feeder from pedestal count only?
No. Use slip count, receptacle ratings, permitted demand factors, phase, neutral load, voltage drop, and NEC 555 safety rules. Ten 30A pedestals do not automatically equal a 300A feeder.
What NEC article covers marina shore power?
NEC Article 555 covers marinas and docking facilities. Designers also check Articles 210, 215, 220, 250, 300, 310, and 406 for conductors, feeders, grounding, wiring methods, and receptacles.
How much voltage drop should dock wiring allow?
A common design target is 3% on a branch circuit and 5% total feeder plus branch. For 120V shore power, 3% is only 3.6V, so long dock branches need careful review.
Does marina wiring need wet-location conductors?
Yes, dock raceways and outdoor waterfront equipment are treated as wet and corrosive locations. Verify insulation such as THWN-2 or listed cable, pedestal listings, and corrosion-resistant fittings.
How does IEC marina sizing differ from NEC sizing?
IEC projects use mm2 conductors, installation methods, grouping factors, protective-device coordination, and IEC 60364-7-709 marina requirements instead of AWG selection alone.
Screen the dock schedule before cable is pulled
Use the voltage-drop, ampacity, and breaker tools to compare code-minimum conductors with practical sizes for stable marina pedestals and dock feeders.