Marina shore power is a wet-location electrical system that carries normal load current through long docks, ramps, floating slips, and pedestal branch circuits before it reaches the boat inlet.

Use this page when the voltage drop calculator is being applied to 30A and 50A shore-power pedestals, 120/240V feeders, 208V three-phase marina distribution, and IEC-style 230V shore supplies where distance, corrosion, load diversity, and code documentation all matter.

TL;DR

Model the full one-way route: service equipment to feeder panel, dock run, pedestal, and boat inlet.
Keep NEC 210.19(A)(1) and 215.2(A)(1) informational-note targets visible: 3% branch and 5% total.
For 50A, 120/240V shore power, a 180 ft dock run can force a jump from #6 Cu to #4 Cu or larger.
Voltage drop does not replace NEC 555 ground-fault protection, wet-location wiring methods, bonding, or corrosion checks.

Key Definitions for Dock Circuits

Shore power is the electrical supply provided from a marina or dock pedestal to a vessel while it is moored.

A marina feeder is a feeder that supplies dock distribution panels, floating structures, or multiple pedestal branch circuits.

A pedestal branch circuit is the final circuit from the marina panelboard or distribution point to one or more shore-power receptacles.

Voltage drop is the voltage lost in conductors because copper or aluminum resistance increases with length, current, and operating temperature.

Sizing Workflow for Marina Voltage Drop

Step 1

Map the actual path length. Include the shore-side service room, ramp transition, fixed pier, floating dock movement allowance, and pedestal whip. Use one-way route length in the calculator.

Step 2

Separate feeder and branch-circuit calculations. A 225A feeder to a dock panel and a 50A pedestal circuit should be checked independently, then reviewed together against the common 5% total design target.

Step 3

Use the real load basis. For a 30A, 120V pedestal, calculate at 24A when the load is treated as continuous at 80%, and check the full 30A where the owner specification requires worst-case receptacle loading.

Step 4

Compare conductor choices before changing overcurrent protection. Upsizing from #6 Cu to #4 Cu can reduce voltage drop while the breaker remains tied to receptacle, cable ampacity, and equipment rating rules.

Step 5

Re-check wet-location wiring method, equipment grounding conductor, bonding, marina ground-fault protection, terminal temperature rating, conduit fill, and available fault current before releasing the design.

NEC and IEC Checkpoints

Use public references for the NEC and IEC background, then verify the enforceable edition adopted by the authority having jurisdiction and the marina owner specification. Background references: the NEC and the IEC .

NEC Article 555 covers marinas, boatyards, floating buildings, and commercial or noncommercial docking facilities, including shore-power distribution and ground-fault protection requirements.
NEC 210.19(A)(1) informational note and NEC 215.2(A)(1) informational note are commonly used as the 3% branch-circuit and 5% total feeder-plus-branch voltage-drop design targets.
NEC 310.16 ampacity tables and conductor temperature limitations still control conductor selection; voltage drop alone never proves a conductor is code-compliant.
NEC 250 bonding and grounding rules remain critical on docks because conductive parts, water, shore equipment, and vessels can create touch-voltage hazards.
IEC 60364 shore-supply projects typically start with current-carrying capacity and disconnection requirements, then check voltage drop for 230V single-phase or 400V three-phase distribution.

Practical Dock Circuit Comparisons

These examples are planning-level comparisons. Enter your exact voltage, phase, conductor, temperature, load current, and one-way route length before selecting a final conductor.

Dock circuit	Trial conductor	Voltage-drop result	Design decision
120V, 30A pedestal, 140 ft one-way	#10 Cu	About 9.2V, or 7.7%	#6 Cu is often checked when the branch target is 3%
120V, 30A pedestal at 24A continuous, 140 ft	#8 Cu	About 5.6V, or 4.7%	#6 Cu gives better margin for weak utility voltage
120/240V, 50A shore-power pedestal, 180 ft	#6 Cu	About 8.9V line-to-line, or 3.7%	#4 Cu is a common next check for a 3% branch target
208V three-phase dock feeder, 80A, 220 ft	#3 Cu	Near 9.8V, or 4.7%	#1 Cu or 1/0 Al may be compared before adding a dock subpanel
230V IEC-style shore supply, 32A, 60 m	6 mm2 Cu	Around 8.5V, or 3.7%	10 mm2 Cu is often needed where the project target is 3%
240V feeder plus 120V pedestal branch	Feeder 2%, branch 2.8%	Total near 4.8%	Acceptable only if the specification allows a 5% total design target

Worked Calculator Examples

30A, 120V pedestal at the end of a 140 ft dock

Enter 120V, single-phase AC, copper, 30A, and 140 ft one-way. #10 copper can land near 7.7% voltage drop, which is poor for a boat air conditioner starting under load. #6 copper can move the branch circuit closer to 3%, while the 30A receptacle and breaker ratings stay unchanged.

50A, 120/240V shore-power pedestal, 180 ft from panel

For a split-phase pedestal, enter 240V line-to-line and 50A for the ungrounded conductor calculation. #6 copper may be around 3.7% over 180 ft. If the feeder already uses 1.5% to 2%, #4 copper is a practical comparison before the total exceeds the 5% planning target.

208V three-phase dock feeder serving several slips

A dock panel feeder at 80A and 220 ft one-way should be checked as three-phase AC at 208V. A trial #3 copper feeder can approach 4.7%, leaving almost no branch-circuit margin. Moving the panel closer, increasing conductor size, or splitting dock loads can be cheaper than accepting low voltage at every pedestal.

Field Review Checklist

Record service-to-dock feeder drop and pedestal branch drop separately, then add them for the total design review.
Use actual installed path length, including vertical drops, flexible connections, ramps, and floating-dock movement loops.
Check conductor material and temperature rating against NEC 310.16, terminal markings, wet-location insulation, and corrosion exposure.
Confirm NEC 555 ground-fault protection, equipment grounding conductor continuity, bonding, and labeling before energizing the dock.
For IEC projects, confirm local marina rules, 30 mA or project-specified RCD protection, disconnection time, and voltage-drop limit before installation.

Common Questions

What voltage-drop limit should a marina pedestal use?

Many designers use the NEC informational-note targets of 3% for the branch circuit and 5% total feeder plus branch. The authority having jurisdiction or marina specification can require a stricter value.

Do I calculate a 50A shore-power pedestal at 120V or 240V?

For a 120/240V split-phase shore-power receptacle, calculate the line-to-line drop at 240V for balanced 240V loading, then review 120V line-to-neutral loads if one leg can be heavily loaded.

Can I solve marina voltage drop by increasing the breaker size?

No. The breaker must match the receptacle, conductor ampacity, equipment listing, and NEC requirements. Voltage drop is normally solved with larger conductors, shorter routes, added distribution points, or load management.

Does NEC Article 555 set the voltage-drop percentage?

Article 555 covers marina and dock safety rules, but the commonly used voltage-drop percentages come from NEC 210.19(A)(1) and 215.2(A)(1) informational notes: 3% branch and 5% combined.

Why are dock circuits worse for voltage drop than normal branch circuits?

Dock circuits often have long one-way lengths, corrosion exposure, flexible transitions, multiple pedestals, and high coincident loads such as air conditioning, battery charging, and water heaters.

How do IEC 230V shore supplies compare with NEC 120V pedestals?

The same volt loss is a smaller percentage at 230V than at 120V. For example, 6V is 5% on 120V but about 2.6% on 230V, so always compare both volts and percent.

Check the Dock Run Before Cable Is Pulled

Run the feeder and pedestal branch separately in the calculator, then compare the total before conduit, cable tray, or floating-dock hardware makes conductor changes expensive.

Open Voltage Drop Calculator NEC Voltage Drop Guide

Marina Shore Power Voltage Drop for Dock Pedestals