AC Safety Tests For Boats

Note;  Major revisions to this post, with additional test added, June 20, 2015.
Note: Editorial and spelling corrections; alternative test added for Test 9B, April 23, 2018

This article describes a series of test measurements intended to be performed safely by boat owners/operators.  Little or no prior knowledge or skills with electricity, electric circuits or the regulatory codes, components, materials, workmanship and techniques involved in installing and servicing AC electrical systems is needed.  There is never a need to contact a “live” electrical circuit.  The tests assess the safety status of a boat’s AC electrical system.  These tests can a) expose non-compliance and/or b) confirm compliance with a key subset of safety elements of the ABYC E11 electrical standard.   Compliance of the boat to ABYC electrical standards is becoming more and more important.  As shore-side facilities upgrade to the requirements of newer versions of the National Electric Code (NEC), boats that do not comply risk being left without AC electric power. For background information on that concern, see my article, “Emerging AC Electrical Concern,” on this website.

NOTES AND CAUTIONS:

  1.  Shore power cords labeled “2-wire plus ground” contain three conductors.  The conductors are individually coated with green (ground), white (neutral) and black (hot) insulation.
  2.  Shore power cords labeled “3-wire plus ground” contain four conductors.  The conductors are individually coated with green (ground), white (neutral), black (hot1) and red (hot2) insulation.
  3.  The testing described in this document is presently limited to AC shore power pedestals and boat shore power circuits equipped with either 1 or 2, “2-wire plus ground,” 120V shore power circuits.  These descriptions do not apply to boats with “3-wire plus ground,” 240V shore power systems.
  4.  The purpose of these tests is merely to IDENTIFY and EXPOSE the presence of conditions that represent immediate or potential ELECTRICAL SAFETY RISKS or create incompatibility with shore power facilities such that shore power may be interrupted to the affected boat.  Boat owners may wish to engage a ABYC-certified marine electrical technician for help in performing or interpreting these tests.
  5.  The fault conditions that these tests can expose have an extensive array of possible causes.  It is not possible to present a practical DIY list of effective corrective action(s).  If fault conditions are identified in testing, it is necessary for electrical novice boat owners to engage an ABYC-certified electrical service technician to perform further diagnosis and corrective actions.
    PERSONS WITHOUT TRAINING IN INSTALLING AND SERVICING MARINE ELECTRICAL SYSTEMS ARE EXPLICITLY DISCOURAGED FROM ATTEMPTING DIY CORRECTIVE ACTIONS.  CORRECTIVE ACTIONS MUST BE PERFORMED BY PERSONNEL WITH TRAINING AND SKILLS IN MARINE ELECTRICAL SAFETY STANDARDS!
  6.  Any boat equipped with two 120V shore power inlets should have these tests performed on both of the incoming shore power circuits.
  7.  These tests require the use of commonly available, inexpensive test equipment:
    • Digital Multimeter (DMM)
    • Clamp-on ammeter
    • AC Circuit Tester
    • Home-made test jig cordset
  8.  NOTE: Tests 1 – 3 are performed on an energized dock pedestal receptacle.  ONLY PERFORM THESE TESTS IF YOU KNOW BASIC ELECTRIC SAFETY AND ARE PERSONALLY COMFORTABLE PROBING A LIVE ELECTRIC CIRCUIT WITH VOLTMETER TEST LEADS.
  9.  Ground and leakage fault currents that originate on a boat may cycle “on” and “off” with the automatic operation of equipment installed on a boat.  Boat owners should have as much of the electrical equipment on the boat in actual operation at the time of testing as possible, including water heater, battery charger(s), range/oven(s), heat pumps, washing machine/dryer, microwave, refrigerator, ice maker, space lighting, entertainment systems, etc.  Equipment that may harbor an electrical fault may not show symptoms unless it is actually running.  If all devices aboard can not be run at the same time, testing may be performed in stages to ensure all onboard electrical equipment is tested.
  10. A “hot basin” is a facility where an “electric charge” exists in the water.  “Hot basins” can have many causes, including:
    • a longterm unattended boat fit with power cord(s) with degraded insulation draped in the water,
    • damaged or degraded dock wiring or dock wiring periodically immersed in basin water, and
    • a nearby boat with an on-board ground fault.  (Ground faults cause power to flow into the water, which will then return to their source on the ground wires of all nearby neighboring boats.)
  11.  This testing does not include DC System tests.
  12.  This testing does not cover DC galvanic currents or the testing or operation of Galvanic Isolator diode packs.
  13.  This testing does not include advanced tests, procedures or test equipment that certified service technicians may utilize.

References to the following items appear in the test procedures:

30A Shore Power Plug/Receptacle Blade Layout: 

Bent Blade   –  Safety Ground (Green)
Shorter Blade –  Neutral (White)
Longer Blade  –  Hot (Black)

L5-30P - Plug L5-30R - Receptacle

L5-30P – Plug
L5-30R – Receptacle

Tests 9, 9A and 9B: 

Clamp-on Ammeter;
Theory of Operation.

Clamp-on Ammeter test configuration for Test 9.

Clamp-on Ammeter test configuration for 120V, 30A  as used in Test 9.

Tests 9A and 9B: Suggested “home-made” test “tool;” this test tool allows access to the individual conductors contained within a shore power cord and at the same time protects against actual contact with live electrical conductors.

Home-made test jig allows access to the three individual conductors of the shore power cord

Home-made test jig allows safe access to the three individual conductors of the shore power cord

Tests 10 and 11:

AC Circuit Tester; a suggested test “tool.”

AC utility outlet tester including GFCI

AC utility outlet tester including GFCI

NOTE: Tests 1 – 3, following, are performed with the dock pedestal receptacle energized (turned “on”).

ONLY PERFORM THESE TESTS IF YOU ARE PERSONALLY COMFORTABLE PROBING A LIVE ELECTRIC CIRCUIT WITH INSULATED METER TEST LEADS.

Test 1:
Purpose of Test 1. Verify the electrical integrity and wiring of the dock feeder wiring to the dockside pedestal;
2. Verify the pedestal’s 30A receptacle connections.The governing electrical standard is NFPA 70 (NEC, Article 555).
Test Setup 1. Shore Power cord(s) disconnected at pedestal and set aside;
2. Pedestal breaker(s) set “on;”
3. Digital Multimeter (DMM) set to measure AC Volts
Test Measurement Points At the pedestal outlet (NEMA L5-30R, 30A):
measure for AC voltage between the Ground and Neutral receptacle contacts.
Nominal Result 0.0 VAC
Possible Findings Less than 5 VAC;
Greater than 5 VAC
Fault Findings Requiring Correction Anything greater than 5 VAC;
(Note: A finding of 120V is an urgent emergency; immediately report this finding to facility management.)
Considerations Affecting Test Setup or Outcome 1. Long length of dock feeder cables;
2. Amount of power being drawn by boats connected to the feeder.
3. Reversed Polarity of Neutral and Hot conductors.
Test 2:
Purpose of Test 1. Verify the electrical  integrity and wiring of the dock feeder wiring to the dockside pedestal;
2. Verify the pedestal’s 30A receptacle connections. Governing standard is NFPA 70 (NEC, Article 555).
Test Setup 1. Shore Power cord(s) disconnected at pedestal and set aside;
2. pedestal breaker(s) set “on;”
3. Digital Multimeter (DMM) set to measure AC Volts
Test Measurement Points At the pedestal outlet (NEMA L5-30R, 30A):
measure for AC voltage between the Hot and Ground receptacle contacts.
Nominal Result 120 VAC
Possible Findings Normal “System Voltage” can range from around 105V to 125VAC;
0.0 VAC
Fault Findings Requiring Correction Less than 105V (hot, summer days; severe “brownout” conditions);
greater than 125 VAC.
0.0 VAC (Note: potential safety issue if open ground; immediately report this finding to facility management)
Considerations Affecting Test Setup or Outcome 1. Demand conditions within the utility distribution system;
2. Long length of dock feeder;
3. Amount of power being drawn by other boats connected to the same dock feeder
4. Reversed Polarity of Neutral and Hot conductors.
Test 3:
Purpose of Test 1. Verify the electrical  integrity and wiring of the dock feeder wiring to the dockside pedestal;
2. Verify the pedestal’s 30A receptacle connections. Governing standard is NFPA 70 (NEC, Article 555).
Test Setup 1. Shore Power cord(s) disconnected at pedestal and set aside;
2. Pedestal breaker(s) set “on;”
3. Digital Multimeter (DMM) set to measure AC Volts
Test Measurement Points At the pedestal outlet (NEMA L5-30R, 30A):
measure for AC voltage between Hot and Neutral receptacle contacts.
Nominal Result 120 VAC
Possible Findings Normal “System Voltage” can range from around 105V to 125VAC;
0.0 VAC 
Fault Findings Requiring Correction less than 105V (hot, summer days; severe “brownout” conditions);
greater than 125 VAC.0.0 VAC (Note: potential safety issue if open ground; immediately report this finding to facility management)
Considerations Affecting Test Setup or Outcome 1. Demand conditions within the utility distribution system;
2. Long length of dock feeder;
3. Amount of power being drawn by other boats connected to the same dock feeder
4. Reversed Polarity of Neutral and Hot conductors.
Test 4:
Purpose of Test 1. Verify the electrical integrity and continuity of the Shore Power Cord and boat AC Shore Power inlet connections
Test Setup 1. Shore Power cord(s) disconnected at pedestal but connected at the boat;
2. Genset(s) “off,” Inverter AC output set “off.”
3. DMM set to measure Resistance (Ohms, Ω). (For convenience of measuring, drag the male end of shore power cord onto the boat.)
Test Measurement Points Measure for resistance and continuity between the Ground blade of the cord’s male plug end (NEMA L5-30P) and the main AC Safety Ground Buss aboard the vessel.
Nominal Result Less than 1 Ω
Possible Findings A range of resistance from 0 Ω to  Ω
(infinity); (missing/defective AC Safety Ground is an urgent emergency)
Fault Findings Requiring Correction Any varying or fixed  value of greater than 1 Ω.

Note: This fault is one of the two that are necessary for boats to  dump AC power into the water; urgent attention is required

Considerations Affecting Test Setup or Outcome Presence of Galvanic Isolator; consult manufacturer for procedures for testing the device’s diode pack. Presence of Isolation Transformer, which is considered an on-board, not shore power, source.  The onboard ground does not connect to the shore power service ground.
Test 5:
Purpose of Test 1. Confirm that the boat’s AC Safety Ground is bonded to the Ship’s common DC Ground.

Governing standard is ABYC E11, 11.17.1.4.3.

Test Setup 1. Shore Power cord(s) disconnected at pedestal but connected at the boat;
2. Genset(s) “off,” Inverter AC output set “off.”
3. DMM set to measure Resistance (Ohms, Ω).(For convenience of measuring, drag the male end of shore power cord onto the boat.)
Test Measurement Points Measure for continuity between the Ground blade of the cord’s male plug end (NEMA L5-30P) and the Engine Block of the Propulsion Engine aboard the vessel.
Nominal Result Less than 1 Ω
Possible Findings A range of resistance from 0 Ω to  Ω
(missing/defective AC/DC system bond; high priority attention required)
Fault Findings Requiring Correction Any varying or fixed value of greater than 1 Ω.
Considerations Affecting Test Setup or Outcome Presence of Galvanic Isolator; consult manufacturer for procedures for testing the device’s diode pack.Presence of Isolation Transformer, which is  considered an on-board power source.  The onboard ground does not connect to the shore power service ground.
Test 6:
Purpose of Test 1. Confirm that cross-connections are not present between the ground buss and the neutral buss for the 120V circuit aboard the boat.

Governing standard is ABYC E11, 11.5.5.1 and 11.17.1.2.

Test Setup 1. Shore Power cord(s) disconnected at pedestal but connected at the boat;
2. Genset(s) “off,” Inverter AC output set “off.”
3. DMM set to measure Resistance (Ohms, Ω).
Test Measurement Points At the cord’s male plug (NEMA L5-30P 30A plug), measure the resistance between Ground and Neutral blades
Nominal Result ∞ Ω
Possible Findings less than 1 Ω
Fault Findings Requiring Correction Any varying or fixed  value of less than ∞ Ω

Note: If the boat is fit with one or more inverter’s which comply with UL458, low resistance (<1.0 Ω) is a normal finding.  It will be necessary to isolate the inverter’s automatic neutral-to-ground bond to complete the test.  The process of isolating the inverter will be unique to the particular inverter manufacturer   If unfamiliar with this process, consult a marine-certified electrical technician for assistance.

Considerations Affecting Test Setup or Outcome 1. Incorrectly isolated genset, inverter or isolation transformer
2. Incorrect selection (design/capability) of device transfer switch
3. Defective Reverse Polarity detection circuit(s);
Test 7:
Note 1: this test does not apply to (cannot be performed on) boats with only one AC Shore Power Cord.
Note 2: this test correlates with Test 9C, which should also be performed if a non-infinity resistance value is found.
Purpose of Test 1. Confirm that the AC Neutrals aboard a boat with two 120V AC shore power circuits are isolated from one another.

Governing standard is ABYC E11, 11.5.5.6.2 and 11.17.1.3.

Test Setup For boats with two 120V shore power circuits aboard:
1. Shore Power cords disconnected at pedestal but connected at the boat;
2. Genset(s) “off,” Inverter(s) set “off;”
3. DMM set to measure Resistance (Ohms, Ω).
Test Measurement Points Measure the resistance between the Neutral blade of Shore Power cord #1 (NEMA L5-30P) and the Neutral blade of shore power cord #2 (NEMA L5-30P)
Nominal Result ∞ Ω
Possible Findings Any range of values
Fault Findings Requiring Correction Any varying or fixed  value of less than ∞ Ω
Considerations Affecting Test Setup or Outcome
Test 8:
Note:
this test cannot be performed on boats with only one AC Shore Power Cord
Purpose of Test Confirm that the AC Grounds aboard a boat with two 120V AC shore power circuits are connected together and continuous with one another.

Governing standard is ABYC E11, 11.17.1.4.2.

Test Setup For boats with two 120V shore power circuits aboard:
1. Shore Power cords disconnected at pedestal but connected at the boat;
2. Genset(s) “off,” Inverter(s) “off.”
3. DMM set to measure Resistance (Ohms, Ω).
Test Measurement Points Measure the resistance between the Ground blade of Shore Power cord #1 (NEMA L5-30P) and the Ground blade of shore power cord #2 (NEMA L5-30P)
Nominal Result Less than 1 Ω
Possible Findings Any range of values
Fault Findings Requiring Correction Any varying or fixed  value of greater than 0 Ω.
Considerations Affecting Test Setup or Outcome
Test 9:
Purpose of Test 1. Determine if abnormal leakage currents are present in the shore power cords supplying power to a boat via two 120V shore power circuits.

Notes:
1. This test is only an easy-to-perform screening test.
2. Any observed fault means that either a) power is being dumped into the water by this boat, b) power is returning to its on-shore source on an unintended conductor, or c) power which has already found its way into the water of the facility’s basin is finding it’s way back to its on-shore source via this boat’s ground system.
3. BECAUSE IT’S NOT POSSIBLE TO DETERMINE WHICH POSSIBLE CAUSE EXISTS WITH THIS SIMPLE TEST, ANY OBSERVED FAULT CONDITION NEEDS IMMEDIATE FURTHER INVESTIGATION.

Test Setup 1. Shore Power cord(s) connected at pedestal and connected at the boat;
2. Pedestal breakers set “on.”
3. All possible boat AC loads turned “on” and actually running/operating.
4. Genset(s) “off,” Inverter(s) set “off.”
5. Clamp-on Ammeter set to measure AC Amps.
Test Measurement Points Sequentially clamp the ammeter around the outer body of each 120V shore power cord.
Nominal Result In salt water, less that 50mA;
in fresh water, less than 25mA. 
If fault current is within above limits, skip to test 10. If fault current readings exceed the above limits, perform tests 9A and 9B.  Also see notes titled, “IF TEST 9 IS POSITIVE,” following below.
Possible Findings A value ranging from 0.0 Amps to several Amps
Fault Findings Requiring Correction Any varying or fixed value greater than 50mA (0.050 Amps) in salt water.
Any varying or fixed value greater than 25mA (0.025 Amps) in fresh water.

Note: There is imprecision and debate among experts around the absolute value of the above numbers.  I feel these recommendations are a reasonable compromise between human/pet life-safety and the practical sensitivity of inexpensive, utility-grade clamp-on ammeters available OTC from community sources (marine chandleries, big box and hardware stores) at prices that lay buyers are willing to pay.  Furthermore, periodic screening checks for ground fault and leakage fault currents is vastly better than never checking, which results in being unaware of the actual presence of a potentially serious problem.

Any doubt about life safety should be immediately referred to a marine-certified electrical technician.

Considerations Affecting Test Setup or Outcome As much of the electrical equipment installed on the boat as possible should be “on,” running and in operation at the time of the test.  This includes water heater(s), battery charger(s), inverter/charger(s), heat pump(s), refrigerator, ice maker, watermaker, range/oven, washer/dryer, lights, entertainment devices, etc.  If it is not possible to run all equipment at the same time, perform this test in multiple steps, each with different equipment running and in operation.  The more equipment that is running at the time of the test, the more comprehensive the test results will be, and the greater the confidence about the results.

Comments on Test 9A:

Test 9A can be performed on boats with either one or two 120V, 30A shore power cords.

On boats equipped with only ONE shore power cord, or when only ONE shore power cord is physically connected between the test boat and the shorepower pedestal at the time the test is performed, a non-zero test finding indicates that power is escaping from the boat into the surrounding water.

On boats equipped with two 120V, 30A shore power cords when both shore power cords are physically connected between the boat and the shore power pedestal, a non-zero test finding is only an indication that abnormal currents are present, but the test does not distinguish between a Ground Fault and a Leakage Fault.

A Ground Fault is a condition that results in power leaking into the water surrounding the boat.

A Leakage Fault is a condition in which power returns to its on-shore source, but it returns on an unintended conductor of the AC system.

Test 9A:
Purpose of Test Determine if fault currents are present. The two types of fault current are:

1. Ground Faults causing power to escape from the boat into the surrounding water (“dumping power into the water”); and
2. Leakage Faults, which are not a Ground Fault, but result in current following an unintended path back to its on-shore source.

Test Setup 1. Install the recommended test tool jig fixture* between the pedestal outlet and the shore power service cord in order to gain access to the three individual shore power conductors (Black, White, Green).
2. Shore Power cord(s) connected at pedestal and connected at the boat;
3. Pedestal breakers set “on.”
4. All possible boat AC loads turned “on” and actually running/operating.
5. Genset(s) “off,” Inverter(s) set “off.”
6. Clamp-on Ammeter set to measure AC Amps.
* The test tool I suggest for this testing is a “home-made,” short 30A “extension cord” fit with an L5-30P male plug on one end and an L5-30R female receptacle on the other end.  Carefully remove about 8” of outer jacket insulation to expose the individual electrical conductors (green, white and black) inside the cord.  Only remove the outer exterior insulation jacket.  Be careful not to cut or damage the green, white and black insulation covering the individual conductors.
Test Measurement Points Install the clamp-on ammeter around BOTH the White and Black wires of the shore power cord at the same time, but excluding the green wire.
Nominal Result 0.0 A
Possible Findings A value ranging from 0.0 A to several amps Any non-zero amps (positive) finding means a fault current is present. If this test is positive with only ONE shore Power Cord physically connected between the boat and the shore power pedestal, it should be treated as an URGENT EMERGENCY.

If this test is positive on a boat with two shore power cords connected between the boat and the shore power pedestal at the time of testing, continue to Test 9B.

Fault Findings Requiring Correction Any varying or fixed value greater than 50mA.
Considerations Affecting Test Setup or Outcome On-board equipment running at the time of the test.  The more equipment that is actually in operation at the time of the test, the more  comprehensive the test results will be.

Comments on Test 9B:

Test 9B is indicated any time a non-zero AC current reading is found in either one of the two 120V shore power cords in Test 9A. The purpose of this test is to differentiate between the presence of a Ground Fault or the presence of a Leakage Fault.

Rationale – Ground Fault:

In order for power to flow from a boat into the surrounding water, two faults must by present simultaneously. The first necessary fault is an open circuit or high resistance in the boat’s green safety ground connection to the shore power infrastructure (identified in Test 4). The second necessary fault is the presence of a condition that has unintentionally energized the safety ground circuit. This can be caused by a wiring error or equipment malfunction aboard the boat.

If the safety ground connection from the boat to the shore power infrastructure is sound, and if incorrect neutral/ground wiring connections are present aboard, fault currents can exist in a hidden, non-symptomatic state. Fault currents which evolve to become symptomatic can be lethal to people and animals in nearby waters.

Defective ground connections are easy to avoid and easy to correct. Ground faults can be very difficult to isolate and identify. Several causes of ground faults can come on over a long period of time. Multiple ground faults can exist at the same time in any electrical system, making isolation and correction extremely costly and time consuming. Identification of ground fault cause is beyond the scope of this article. Diagnosis and correction of ground faults requires advanced electrical skills and electrical diagnostic experience. If Test 9A confirms this condition aboard a boat, the professional services of a certified marine electrical technician should be engaged.

Rationale – Leakage Fault:

If the neutral conductors of a boat with two 120V AC shore power circuits are cross-connected, a potential parallel path for AC current returning to the on-shore source is created between the two circuits. That potential parallel path becomes an actual parallel path when BOTH shore power cords are physically connected between the boat and the shore power pedestal. The actual parallel path created by cross-connected neutrals is present even if only one of the pedestal disconnect breakers is set “on,” and/or even if the main disconnect breaker aboard the boat is set “off.”

Cross-connected neutrals create Leakage Faults. Leakage Faults result in AC current flowing in conductors where it is not, at that time, intended to flow (the other neutral). This condition it is not a Ground Fault and does not result in power flowing in the water surrounding the boat, but it will result in tripping a Ground Fault Protection (GFP) device.

Cross-connected neutrals are also a fire risk. If one of the neutrals were to become compromised, the other would take over the load intended to be carried by the failed neutral conductor. With both 120V, 30A circuits highly loaded, the remaining neutral conductor would be significantly overloaded. For example, assume the house circuit is loaded at 18 amps and the heat pump circuit is loaded at 26 amps. In the normal case, with conductors rated at 30A, both circuits are operating within their safe ampacity. But with cross-connected neutrals, if one of the neutrals were compromised or open, the worst case is that the other neutral would carry all of the current of both circuits, or 18 + 26 = 44 Amps. Now, that neutral conductor is operating well above it’s safe ampacity, will overheat, and would cause a fire.

Test 9B:
Note 1: this test does not apply to (cannot be performed on) boats with only one AC Shore Power Cord.
Purpose of Test Differentiate between positive fault findings to identify either:
1. a Ground Fault leaking current into the water, or
2. a Leakage Fault returning power to its source on an unintended conductor.
Test Setup 1. Install the recommended test tool jig fixture* between the pedestal outlet and the shore power service cord in order to gain access to the three individual shore power conductors (Black, White, Green).
2. Shore Power cord(s) connected at pedestal and connected at the boat;
3. Pedestal breakers set “on.”
4. All possible boat AC loads turned “on” and actually running/operating.
5. Genset(s) “off,” Inverter(s) set “off.”
6. Clamp-on Ammeter set to measure AC Amps.
* The test tool I suggest for this testing is a “home-made,” short 30A “extension cord” fit with an L5-30P male plug on one end and an L5-30R female receptacle on the other end.  Carefully remove about 8” of outer jacket insulation to expose the individual electrical conductors (green, white and black) inside the cord.  Only remove the outer exterior insulation jacket.  Be careful not to cut or damage the green, white and black insulation covering the individual conductors.
Test Measurement Points Install the clamp-on ammeter around the White and Black wires of BOTH shore power cords at the same time, but excluding the green wires. In this setup, you will have clamped around BOTH black wires and both white wires; four wires in all.

Test Setur for Test 9B

Measurement configuration for Test 9B

Nominal Result 0.0 A
Possible Findings A value ranging from 0.0 A to several amps A non-zero finding in excess of 50mA means a ground fault defect on the boat is dumping AC power into the water. Significant leakage can be lethal to swimmers, divers and pets. This finding is an URGENT EMERGENCY.

A zero amp finding means all power is returning to shore, and no power is being lost to the water. However, because the measurements in the INDIVIDUAL CORDS were not 0.0A, this finding means the neutrals for the two shore power circuits are cross-connected on the boat.

Fault Findings Requiring Correction Any varying or fixed value greater than 50mA.
Considerations Affecting Test Setup or Outcome On-board equipment running at the time of the test.  The more equipment that is actually in operation at the time of the test, the more  comprehensive the test results will be.

Note: There is also an  alternative way  to get the result provided by test 9B. It is easier, but requires more interpretation on the part of the person doing the testing.   It is very useful if the shore power cords have clean contact blades making good electrical contact.   If blade surfaces or contacts are degraded, it can be less clear. In the hope that it may be useful for some, following is how to approach it.
When the neutrals of two 30A shore power circuits are cross-connected on the boat, they create a parallel path back to the shore power source.   To perform this alternative test, connect both of the shore power cords to the pedestal outlets, but turn power “on” for only one cord.   I like to power the heat pumps, because the compressors and raw water circulator create a large and obvious load.   For this example, let’s assume that the heat pump circuit draws 26 amps. Normally, that 26 amps should return to shore ONLY on the neutral conductor of the heat pump shore power cable, but if the two neutrals are paralleled on the boat, 1/2 the current will return on shore power cord A and 1/2 the current will return on shore power cord B.

With power applied to, and load on, only one shore power cord, clamp each individual shore power cord, one after the other.   If they make good electrical connections and show nearly identical ampere readings, that is a telltale that they are paralleled aboard the boat.   That is, they are cross-connected together, in error, on the boat.   In the above example, the total of 26 amps for the heat pumps would divide and return to shore on both neutral conductors.   The meter would read 13 amps on EACH  individual cord, but if both cords were clamped at the same time, the reading would be 0.0 amps.

Yes, this condition will absolutely trip a GFP sensor on a dock pedestal.

Test 9C:
Purpose of Test 1. Definitively determine if power is entering the boat’s grounding system from the water in which the boat is floating (“hot” basin).
Test Setup 1. Install a test tool jig fixture* between the pedestal outlet and the shore power service cord in order to gain access to the three individual shore power conductors (Black, White, Green).
2. Clamp-on ammeter set to measure AC Amps
* The test tool I suggest for this testing is a “home-made,” short 30A “extension cord” fit with an L5-30P male plug on one end and an L5-30R female receptacle on the other end.  Carefully remove about 8” of outer jacket insulation to expose the individual electrical conductors (green, white and black) inside the cord.  Only remove the outer exterior insulation jacket.  Be careful not to cut or damage the green, white and black insulation covering the individual conductors.
Test Measurement Points Clamp around ONLY the Green wire of the shore power cord, excluding both the Black and White wires.
Nominal Result 0.0 A
Possible Findings 0.0 A up to several amps Any positive finding means that AC power is flowing from the water of the facility’s basin back to shore through the boat’s ground system.  This is a “hot basin,” which can be caused by a fault in the shoreside infrastructure or by AC power leaking into the water from a neighboring boat.
Fault Findings Requiring Correction Any non-0 A value
Considerations Affecting Test Setup or Outcome Report this finding to facility management.
Test 10:
Purpose of Test Verify the integrity and wiring of various on-board AC utility outlets.
Test Setup 1. Shore Power cord connected to pedestal; pedestal breaker set “on;”
2. All utility branch circuits set “on” at the boat’s AC breaker.
3. Test device is an AC Circuit Tester.
Test Measurement Points Insert the circuit tester into any energized outlet receptacle.
Nominal Result Indicator lights show “Normal” condition.
Possible Findings Indicator lights reveal abnormal condition.
Fault Findings Requiring Correction Indicator lights reveal abnormal condition.
Considerations Affecting Test Setup or Outcome n/a
Test 11:
Purpose of Test Verify correct operation of all GFCI-protected outlets.Governing ABYC Standard for minimum GFCI protection is E11, 11.13.3.5.
Test Setup 1. Shore Power cord connected to pedestal; pedestal breaker set “on;”
2. All utility branch circuits set “on” at the boat’s AC breaker.
3. Test device is an AC Circuit Tester.
Test Measurement Points With the AC circuit tester inserted into an energized outlet and displaying normal circuit condition, depress the “GFCI test” button.
Nominal Result Circuit should instantly de-energize
Possible Findings  Circuit fails to de-energize.
Fault Findings Requiring Correction Circuit fails to de-energize.
Considerations Affecting Test Setup or Outcome Test does not apply to outlets not protected by GFCI device.

IF TEST 9 IS POSITIVE:

Test 9 by itself is AT BEST a “screening test.”  Any non-zero reading of AC amperage is only an indication that more testing is required. The cause(s) of a non-zero reading could be aboard the boat in the boat’s electrical system or it could be in the shore power infrastructure of the facility basin waters surrounding the boat. If Test 9 is “positive,” what a boat owner/operator does next may be informed by the following considerations:

  1. If these tests have never been previously performed, a test cordset that allows access to the individual black, white and green conductors of the shore power cord is required for Tests 9A, 9B and 9C. If a test cordset is not available or cannot be borrowed, an electrical layman may want to call in a qualified service technician to continue diagnosis. Any non-zero result for Test 9A is an indication of an electrical fault on the boat. Electrical faults are dangerous, and can develop on any boat at any time.  Electrical faults on a boat will require technical electrical skills to resolve.
  2. If the boat owner has been performing periodic screening tests of the shore power cords, and there is a history of normal Test 9 clamp tests (0 Amps), then there is a high confidence (not 100%, but high) that the boat is correctly wired. Additional testing is required to rule out the recent onset and development of a net-new fault condition.

When out cruising, cruisers are constantly encountering new facilities.  Owner/operators of otherwise fault-free boats would expect to experience “normal” screening tests (less than 50mA) in all facilities.  The logic is, the boat is known from previous testing to be fault-free, and the new basin is assumed to be fault-free. If one encounters a positive screening test at a new facility:

  1. If staying at a facility as an overnight or short-term transient guest, one may opt to “just ignore” this single finding. One can’t be certain, but because there is a known history of normal tests on the boat, this case is probably caused by a hot basin at the facility. When the boat is subsequently relocated to another facility, re-test to confirm. The probability of encountering two hot basins in a row is very low, but not absolutely zero. If a positive test result follows the boat and recurs at a new location, the owner should then perform both tests 9A through 9C.
  2. If one encounters a positive test when clamping their own boat’s shore power cords, then clamping around the shore power cord(s) of the immediate dock neighbor (whether 30A or 50A; the normal reading in either case is less than 50mA) is advised.  If non-zero readings are also present there, although one can’t be absolutely certain, in the case of a boat with a known fault-free history, it’s likely the facility basin is hot.
  3. If one observes fault readings on both the test boat and a neighboring boat(s), the owner should disconnect their shore power cords from the pedestal and re-check the dock neighbor’s cord(s). If the fault reading at the neighbor’s cord is gone, that suggests the test boat could be the source of the fault current. Unchanged non-zero readings at the neighbor’s cords suggests a hot basin. Reconnect the test boat and re-check. Unchanged non-zero readings at the neighbor’s cord(s) means the test boat is not the source of the fault current.
  4. If one has confidence that an on-site facility employee will understand the subject, report the observed condition to have management check for a hot basin. However, it’s important to talk to someone knowledgeable, generally not “kids” who work afternoons/weekends.  If staying at a facility as an overnight or short-term transient guest and only “kids” are available, call back to the office later and talk to someone who is knowledgeable, or at least responsible enough to pass the concern on to someone who is knowledgeable.
  5. For long-term facility stays, boat owners should periodically check their own cords and those of immediate dock neighbors. If all of these cords show non-zero fault currents flowing, perform Tests 9A thru 9C. Report positive 9C findings to a responsible facility employee to have the basin checked.
  6. For long-term facility stays, boat owners should periodically check their own cords as other transient boats come and go.  I have been able to identify boats with ground-fault problems just by screening my own cords.  If a “hot boat” slips near me, I’ll see that in the readings of my own known-good cords.

An AC fault current flowing in the water of a boat basin generally won’t hurt the underwater metals of boats, but because current is flowing through the water, it is obviously dangerous to swimmers and pets.

NEVER SWIM IN A MARINA BASIN, AND NEVER ALLOW CHILDREN OR PETS TO DO SO! Divers, beware always!

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11 thoughts on “AC Safety Tests For Boats

  1. Chas McKeown

    Jim,

    Thanks for this.

    Do these procedures also apply to 50amp?

    Thanks,

    Chad

    Reply
    1. gilwellbear Post author

      Chad,

      This article as written does not apply directly to 240V, 50A shore power service for boats.

      That said, many of the concepts are the same. Principally among them, when on shore power, neutrals and grounds must not be cross-connected on the boat, so that affects the choice of switch gear installed aboard which is used to switch between shore power, inverter and genset operation. Tests 9, 9A and 9B would be done the same way: 9 is the same, clamping around the outside of the entire 50A cord; 9A is clampped around white, red, black, but excluding green; 9B is the same (green-only, excluding everything else). Also, the AC safety ground must be connected to the DC negative buss.

      But some stuff is different. “Reverse Polarity” would have a different meaning in a 240V system, and what constitutes a “nominal” voltage reading is more complicated. For example, both 120V/240V and 120V/208V are “nominal” for boats, but both 240V and 208V can also be indications of a fault, and it’s up to the boat owner to know when these readings are OK, and when they aren’t, and why.

      I do encourage owners to retrofit ELCI. Once past any installation hurdles, ELCI will eliminate the concern for hidden ground faults aboard. Hidden ground faults – even though not causing symptoms – are still ground faults. They are lurking safety hazards, and will cause power loss/denial in GFP-complying marinas and boatyards

      I plan to work up an addendum with a set of tests for 240V, 50A users. It was just too much to bite off all at one time. Just finding a presentation format that would work took significant effort, and tables are not supported by free WordPress, so I had to learn the HTML to work with them. Still learning, but it keeps my mind occupied.

      Jim

      Reply
    1. gilwellbear Post author

      Hi Phil,
      My article entitled, “Emerging AC Electrical Concern,” is also published in this month’s issue of the MTOA Turtle Times. Feedback appreciated!

      Reply
      1. Phil Johnson

        I just read it last night, our St. Brendan’s Isle mail delivery just came in. Nice coverage on background, as you know the shore side code continues to evolve in committee. And it seems like everyone has an opinion. I’ve kept in touch with David Rifkin, the engineers at Eaton, MEE, Bellingham, Bender, and even Ed Sherman. There are actually two thresholds to work with, current and time, and both need to play in a successful selective tripping system which isolates at the lowest common denominator. In addition the salinity of the marina water both effects the risk ESD’s and the approach to monitoring and isolation. Also the technique used to determine leakage is important as some systems just measure flow on the ground line, while others use a kirchoffs sum to determine losses. We have developed several mitigation schemes to allow power-leaking transients to dock at the new yacht club marina, while we wait for the reworked power system to be completed.

  2. bwehmer

    Great article and easy to comprehend for us novices! Thanks for the contribution.

    Reply
  3. Pingback: Boat A/C safety tests for novices | Nautical Endeavors

  4. Paul Marttila

    Jim –

    Very, very good article. I am not a boat owner, but an electrical engineer. Last summer, I spent several weeks along with another electrical engineer inspecting and documenting electrical systems for many of the Michigan State owned harbors; performing many of the “tests” listed in your article. It is refreshing to see there are boat owner’s out there that recognize the issue. The most common story we were told was that the marina (shore power system) is at fault…..

    And by the way, the 2017 National Electrical Code (as proposed right now) would add the ground fault protection requirement to all residential marinas as well.

    Paul

    Reply
    1. gilwellbear Post author

      Hi Paul,

      Thank you for your generous comment.

      Splitters that are pervasive in the market today add a new dimension to all this, too.

      Consider the case of a boat with two 120V shore power circuits, AND a true leakage fault caused by the two neutrals being cross-connected on the boat. A splitter that adapts two 120V females to a single 50A male at the pedestal brings the neutrals back together outboard of the 50A EPD. That in turn masks the presence of the true fault.

      With a 50A shore power service fed by a reverse wye splitter connected to two 120V feeds – either “smart wye” or “dumb” – clamping the 120V cord segments can/will yield misleading results. This case appears exactly as the case of a boat with two 30A cords with the neutrals connected together on the boat, so current splits, returns in the parallel neutrals, and gives false positive conclusions.

      But, it’s still way better than what we’ve had from a safety perspective, and it will force owners to clean up their boats.

      Reply
  5. Robert Webb

    Thanks for your website; well written, logical, instructive – and enjoyable. I’ve only been in boating for 3 years and your organized information is helpful [I have a 1988 Trojan International 12M w/ twin Cat 3208 TA375/435hp, into which we too have invested a fair chunk of change].
    Question re your AC Tester: can any clamp ammeter be used [I have a Mastech] or do I need the expensive one from Fluke [the model 360 specifically for leakage tests]?
    Thanks again.
    Rob

    Reply
  6. gilwellbear Post author

    Rob,

    For screening testing, any reasonable quality clamp-on tester will work, and if yours has a scale(s) rated for 0mA – 1000mA range, it’ll be fine for screening. I use a Sears clamp-on ammeter. To be truly diagnostic, a laboratory quality instrument like Fluke is needed. My sears probably does lose some precision at levels of less than 100mA. My assumption is, the “average boat owner” isn’t going to try to remediate AC electrical leakage problems DIY. The average boat owner – the audience to which I try to write – isn’t going to be willing to invest in a Fluke quality meter, but I do want everyone to invest in a meter that will do the screening job. For the average boat owner, the Sears unit is fine; good enough for screening. If the screening tests expose a problem, I recommend boaters call a professional to take it from there.

    Jim

    Reply

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