A dock electrical leakage assessment can show whether current is leaking from specific circuits, boats or equipment at the time of the test, and whether ground-fault devices work. It cannot certify that the water around a dock will stay safe, find faults that only appear under other loads or conditions, or replace an inspection against the code your jurisdiction has adopted. Commission one with a written scope: which circuits, which boats and loads, which instruments, which code edition, and what records you get back.
Evidence label: Documentation-based guide. ClearTrade Report Editorial Team checked NFPA, U.S. Consumer Product Safety Commission, state agency, local government and instrument manufacturer documents on November 2, 2026. No hands-on testing, site visit or outside professional review was performed. Instruments and equipment named below are documentation examples, not recommendations. This guide contains no affiliate links.
Why dock leakage matters
NFPA describes the hazard this way: “Electric shock drowning (ESD) can occur when faulty wiring sends an electrical current into the water.” Tennessee’s State Fire Marshal’s Office says ESD “occurs when a swimmer unknowingly enters water that has been electrified by a nearby power source.”
Fresh water is the main concern. An NFPA Journal column (Summer 2022) says “ESD tends to occur more frequently in freshwater environments such as lakes and ponds than in salt water.” The National Association of State Boating Law Administrators explains that “The human body is a better electrical conductor than fresh water,” and that it can take “as little as 10-20 milliamps passed through the human body to cause the muscles to seize.” Tennessee advises: “Never swim within 100 yards of any freshwater marina or boatyard.”
What the electrical code asks of docks
Marinas, boatyards and docks are covered by Article 555 of the National Electrical Code (NFPA 70). Requirements change between editions, and states and cities adopt editions on their own schedules, sometimes with amendments, so the first question for any assessment is which edition and local amendments apply.
Recent editions show the direction of change. According to the NFPA Journal column, the 2020 NEC added docking facilities, alongside marinas and boatyards, to the areas covered by its ESD warning provisions, and added a GFCI requirement for boat-hoist outlets intended for “marine areas that include residences with private docks,” which “may have electrically powered boat hoists that can introduce low-level AC current into the water.” The column says the 2020 edition also set ground-fault protection of equipment (GFPE) “not to exceed 100 milliamperes on feeders and branch circuits,” and required shore-power receptacles to have individual GFPE devices “set to open at currents not exceeding 30 milliamperes.” The same column reports new language requiring facilities with more than three shore-power receptacles “to have a leakage current measurement device available on site,” and a warning sign reading “WARNING-POTENTIAL SHOCK HAZARD-ELECTRICAL CURRENTS MAY BE PRESENT IN THE WATER.”
For the 2023 edition, NFPA’s Tentative Interim Amendment 23-6 to section 555.35 states: “Listed GFPE, rated not more than 100 milliamperes, shall be provided for sources directly supplying all docking facilities or wharfs,” and “Coordination with downstream GFPE shall be permitted.” It also says that where shore power equipment includes a leakage indicator and leakage alarm, “a separate leakage test device shall not be required.” Ask your electrician and the authority having jurisdiction (AHJ) to confirm the exact requirements for your edition. If you are comparing ground-fault rules elsewhere on a property, see our guide to GFCI protection by location and code edition.
What a leakage measurement can establish
Most dock leakage checks use a leakage clamp meter on energized circuits. Fluke’s guide to leakage measurement explains the method: “Test single-phase circuits by clamping the phase and neutral conductor,” and “Test three-phase circuits by clamping around all three-phase conductors.” Clamped together, “the magnetic fields produced by the load currents cancel each other out,” so “Any imbalance current comes from leakage from the conductors to ground or elsewhere.” To measure leakage on the ground path, Fluke says to “place the clamp around the ground conductor.”
Leakage clamps resolve very small currents. Hioki’s CM4002/CM4003 manual says the 6.000 mA range is included “to ensure the measurement with a high resolution of 1 µA,” and Fluke lists its 368 clamp at a “Highest resolution of 1 μA.” That makes it practical to compare circuit by circuit, slip by slip, and boat by boat.
Done well, a measurement session can establish: which circuits or connected boats showed leakage, how much, under what loads, at what time; whether GFCI or GFPE devices tripped when tested; and whether the facility has the leakage measurement device, signage and protection its adopted code calls for.
What a single assessment cannot establish
A reading is a snapshot. Fluke notes that “the amount of leakage current varies depending on how the equipment is operating,” and that “Such intermittent problems can be difficult to diagnose.” Hioki’s manual warns that zero-phase leakage readings are “affected by the load current,” that “If the jaws are even slightly open, errors occur in the measured value,” and that displayed values “can frequently fluctuate due to induction potential even when no voltage is applied.” It describes using an external power supply “to record the measured value for an extended period of time” with the CM4003.
Different tests answer different questions. Fluke notes that an insulation tester “uses a dc voltage for testing, which does not take the capacitive effect into consideration,” so an insulation-resistance result on a de-energized circuit is not the same as a leakage reading under normal operation.
A measurement can also detect a hazard without locating its cause. In an undated update on current reported in Lake Sunapee, New Hampshire, the Town of Sunapee wrote that “Readings taken between the aluminum dock and the water have been between 0 and 1.8 volts,” that “The voltage was present whether the power was turned on or off,” and that “No issues were found with ground grid, transformers, or infrastructure.” Boats that arrive after the test, new equipment, storm damage and seasonal changes can all change the picture.
State rules and routine testing
Some states add their own requirements. For public marinas, harbors and docks, Tennessee’s State Fire Marshal’s Office says: “By law, marina inspections by the SFMO occur every 5 years.” For boat docks and marinas as its code defines them (privately owned docks used only by the owner and guests for noncommercial purposes are excluded), West Virginia requires 110 or 220 volt AC wiring to be installed and maintained by a licensed electrician and requires the sign “ELECTRIC SHOCK HAZARD RISK: NO SWIMMING WITHIN 100 YARDS OF THE BOAT DOCK.” Check your state fire marshal, boating agency and local building department.
Routine device testing fills the gaps between assessments. The U.S. Consumer Product Safety Commission’s GFCI fact sheet says to test GFCIs “At least once a month.” Michigan’s DNR says to “Test GFCI and ELCI protection as recommended by the manufacturer,” and to “Notify the harbormaster of any electrical safety hazards so they can be fixed.” Tennessee advises boaters: “Have your boat tested once a year to see if it is leaking electricity,” and to “Test the ELCI at least once a month or per the manufacturer’s specifications.” The Missouri State Highway Patrol advises having “both the dock and the power supply to the dock being inspected regularly by a qualified electrician.”
What to put in the scope when you commission an assessment
| Scope item | What to ask for | Why it matters |
|---|---|---|
| Code basis | NEC edition and local amendments the AHJ enforces; any state marina or dock law | Ground-fault levels, signage and leakage device rules differ by edition and state |
| Who performs it | Licensed electrician or qualified inspector, as your state requires | Some states require licensed installation, maintenance or inspection |
| Circuits and loads | List of feeders, branch circuits, pedestals, boat hoists and pumps measured, with loads running at the time | Leakage varies with what is operating |
| Boats | Which boats were connected and measured, by slip | Boats connected later are outside the result |
| Instruments | Make, model, range, resolution and calibration date | Lets you compare future readings and judge the measurement |
| Device tests | GFCI, GFPE and ELCI trip tests and results | Shows protection works, not only that it is installed |
| In-water checks | Whether any voltage-in-water measurement was taken, where, how and with what limits stated | A reading at one spot and time is not a guarantee |
| Findings and records | Readings by circuit and boat, photos, deficiencies, corrective actions and a retest plan | Creates a baseline for the next assessment |
Ask the assessor to state in writing what the report does not cover. A clear “not established” list is a sign of an honest scope.
Know the limits of this guide
Evidence label: documentation-based guide. ClearTrade Report Editorial Team checked the sources below on November 2, 2026. We did not visit, measure or test any dock, marina or instrument. We could not read NFPA 70 or NFPA 303 in full, and we did not find a primary source for the 2026 NEC text; confirm current requirements with your AHJ. Electrical work near water is dangerous; only qualified people should open, test or repair dock electrical equipment.
Primary references checked November 2, 2026: NFPA, “Protect Yourself from Electric Shock Drowning”; NFPA Journal, Summer 2022, p. 61; NFPA, Tentative Interim Amendment TIA 23-6 to NFPA 70 (2023), section 555.35; National Association of State Boating Law Administrators, ESD resources; Tennessee State Fire Marshal’s Office releases (March 9, 2015, and May 22, 2026); West Virginia Code, Chapter 20, Article 9; U.S. Consumer Product Safety Commission, “What Is a GFCI?” fact sheet; Michigan DNR, “Electric shock drowning”; Missouri State Highway Patrol release, March 2, 2021; Town of Sunapee, NH, update on electrical current reported in Lake Sunapee; Fluke, “Leakage Current Measurement Basics” and Fluke 368 product page; Hioki CM4002/CM4003 instruction manual (CM4002A961-00).
Frequently asked questions
What is electric shock drowning?
NFPA says electric shock drowning can occur when faulty wiring sends electrical current into the water. It is mainly a fresh water hazard; NFPA’s journal says it tends to occur more often in lakes and ponds than in salt water.
What does a dock leakage assessment measure?
Usually leakage current on energized circuits, measured with a leakage clamp around the circuit conductors or the ground conductor, plus trip tests of GFCI, GFPE or ELCI devices. It shows leakage on the circuits, boats and loads present during the test.
Can a passing leakage test prove the water is safe?
No. Leakage varies with what equipment is operating, intermittent faults can be missed, and boats or equipment connected later are not covered. Treat a result as a dated baseline and keep up routine device testing and periodic reassessment.
Which code applies to my dock?
NEC Article 555 covers marinas, boatyards and docks, but the edition and amendments your state or city adopted control. Some states, such as Tennessee and West Virginia, add their own inspection or signage rules. Ask your authority having jurisdiction.
Disclaimer: This guide is general information based on standards-body, government and manufacturer documentation, not professional electrical, engineering, legal or safety advice for a specific dock or marina. Follow the code adopted where you are and manufacturer instructions, and use a licensed electrician or qualified inspector for any testing or repair. AI tools assisted with drafting. ClearTrade Report Editorial Team checked the cited sources and edited this guide. No hands-on testing was performed.
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