Electrical Safety Letter

The following text is from a 5 December 2011 letter sent by Al Peterson, Kedge (43) to the LNVT Owners Association. The focus is on how an electrical ground fault can result in fire and is also potentially deadly to swimmers near the boat.

Additional information about ground faults can be found at:

  1. Nigel Calder's 'Ground Fault, Interrupted', Part 1
  2. Nigel Calder's 'Ground Fault, Interrupted', Part 2
  3. Nigel Calder's 'Ground Fault, Interrupted', Part 3
  4. Nigel Calder's 'Ground Fault, Interrupted', Part 4
  5. Highpoint Marina Ground Fault Warning
  6. Boat Keeper AC Electrical Safety


7411 West Franklin Avenue
St. Louis Park, MN 55426
Tel 952 546 6028
5 December 2011

Dave Howell, President LNVT Owners Assoc.

The U.S. Coast Guard has been interested in preventing drowning deaths related to electricity in water adjacent to boats in marinas. They gave a grant to the American Boat & Yacht Council Inc. (ABYC) in 2003 and a second grant in 2006 to study the problem. ABYC engaged Quality Marine Services located in Jacksonville, Florida to study the problem in 2006. This letter contains information from the report authorized in 2006.

Quality Marine Services tested boats and water composition in fourteen marinas throughout the United States and prepared an extensive report on the tests. The report prepared by Quality Marine Services lists many electrical related drowning accidents that have occurred. In addition they list many "Close Calls" with no fatalities. There probably were electrical related drowning deaths that were not but should have been attributed to an electrical issue. There were no drowning deaths in the list occurring in salt or brackish water. There were no drowning deaths resulting directly from a boat with a ground fault that was getting power from their own generator. The fatalities
occurred because the amount of electricity passing through the body resulted in the person becoming paralyzed and losing control of his muscles. The "Close Calls" resulted in a tingling in the body but no fatality.

The danger in fresh water may be explained as follows: Electricity on a boat receiving power from shore will enter through the black wire in the shore power cable and generally return through the white wire to its source on shore. If a ground fault (short circuit) occurs on a boat, some and perhaps all of the return electricity will follow or attempt to follow a path to its source through the water. Since fresh water is a poor conductor of electricity there is a voltage gradient (decrease in voltage) between the boat and shore. There is a potential danger of a fatality w~en the voltage gradient is 2 volts per foot or larger and the current is 100 milliamperes or larger. A six foot person could have a 12 volt potential difference from one end of his body to the other. The conductivity of electricity in salt or brackish water is sufficiently high to prevent the voltage gradient to increase above 2 volts per foot. There must be two faults to create a dangerous situation. In addition to the short circuit ground fault listed above, the second fault is a break in the grounding bonding system back to its source through the shore power cable. The bonding system consists of conductors inside the boat with small resistance connecting all underwater metal to the shore grounding green wire in the shore cable. A majority of the current will return through the grounding green wire during a short circuit unless there is a break in this system. If there is no break in the grounding system, the percentage of current returning through the bonding system to the shore power green wire is sufficient to prevent a fatality. However there are many areas on and between the boat and the power source on shore that could be defective which could contribute to a fatality.

Let us expand on dangers of power from gensets. Electricity powered from a genset will return to that genset through available means. There was a "Close Call" on one of several boats being powered through cables from a genset on another boat. Electricity on a boat that had a ground fault was returning to the boat with the genset and resulted in a "Close Call" on a swimmer. It may be added that the neutral wire in a genset should be grounded to the genset. The neutral wire from shore power system is never grounded on a boat. Boats in salt and brackish water are not completely safe from electric faults. The danger of boats with a ground faults in salt water lies in heat creating a fire. The National Fire Protection Agency (NFPA) may expand on this problem.

A bonding system in good condition does not insure that no problems exist. A boat with a ground fault may slowly destroy the sacrificial zincs and other underwater hardware on the neighboring boat.

The Safety Committee in the 298 slip St. Croix Marina (SCMC) where we reside in the summer has volunteered to check boats for ground faults when requested by the owners. There has been several years of limited success in obtaining owner requests. The check was accomplished with a GFCI inserted between the shore power pedestal on the dock and the boats power cable. The SCMC Board of Directors recently voted to provide a financial incentive for owners to have their boats checked this coming season. Ground fault short circuit has been the only item checked in the past. Future checking will be expanded to insure continuity between the underwater gear bonding system and the shore green wire grounding system. We have had two known "Close Calls" in our marina in the past six years. The first problem occurred with an adult in the water behind his boat, and the second occurred on another pier with three youngsters swimming behind their boat.

Let me share my personal history regarding electricity and drowning. I first learned of the problem thirty or forty years ago when it was reported that a man in South Eastern Wisconsin drowned as a result of electrically charged water. I searched for a method to check boats and finally found that Nigel Calder offered a method. I checked our Lord Nelson hull #43 and discovered a ground fault. Both the bake and broil heating elements in the Princess stove was shorted to ground. I contacted Mr. Lon Schultz of Seaward four or five years ago, and presented the problem to him. We had many non conclusive conversations, and finally Mr. Schultz would not accept my calls. I removed the broil element and insulated the bake element from ground to permit us to continue using the oven. Two years ago Mr. Schultz contacted me and reported that he had found a source for heating elements that were not grounded. He was kind enough to send these elements to me free of charge. I have checked our Lord Nelson by Nigel Calder's method (see Ground Fault, Interrupted Parts 1-4 above) every year since I learned that he had a method.

This information is forwarded to you in the event that you feel our LNVT members should learn about the dangers of electricity near water.

What should be done:

1) Certainly space is limited in the Tuggers newsletter. The amount of information in this letter may be reduced and published in the newsletter.
2) The information in this letter may be split and published in separate Issues.
3) We can ignore the problem. My insurance company reported in the October issue of Seaworthy that there have been five fatalities in the U.S.A. this year. Perhaps the risk of a fatality is small enough that we may ignore the problem.
4) Perhaps you have a suggestion

There has been very little enthusiasm in our marina about these dangers, and perhaps the Lord Nelson owners would show the same lack of enthusiasm. Let me know if you think that we should proceed, and if so how do we do it? The ABYC report is 5/8 inch thick. I never counted the number of pages, but it may approach 200. I will provide the Coast Guard source of the report if you want to study it.

Al Peterson


credit: Nigel Calder

The following is an abreviated version of the tests described by Nigel Calder in his 'Ground Fault, Interrupted' article, pages 70-77, which appeared in Professional Boatbuilder, April/May 2006.

For clarity we'll assume that an AC circuit has three wires: hot (black); neutral (white); and ground (either green or without insulation).

6a. We'll first make sure that the ground line from the shore-power cord is electrically connected to the boat. Plug the shore-power cord into the boat but not into the dock. With the meter set on its lowest ohm reading, measure between the ground lead on the shoreside end of the power cord and the boat's AC ground bus in the electrical panel (the ground lead on any boat outlet will surfice too). The reading should be 1 ohm or less.

Exceptions: an isolation transformer will yield infinite ohms; a galvanic isolator may result in high or fluctuating ohm readings. To confirm the galvanic isolator is working properly, set the meter for diode testing, place the leads per above, and confirm the reading is about .9V. Reverse the leads and confirm .9V again. Any other values and the galvanic isolator isn't working correctly.

6b. Now we're going to make sure that the ground line from the shore-power cord is electrically connected to the engine. With the meter set on its lowest ohm reading, check the resistance between the grounding lead on the shoreside end of power cord and the engine. The reading should be 1 ohm or less. More than this there's a problem. If the reading is infinite ohms, i.e. no connection between AC grounding and DC ground there's a big problem.

7a. Now we're going to see how much galvanic current is going through the boat. With the meter measuring DC amps, put one lead on the shore-power cord grounding line and the other on the shore-power's grounding line. Anything less than 30mA meets ABYC standards—however, 0mA is probable and 2 to 5mA is as much as we want to see. Over this amount a galvanic isolator is needed.

7b. Now we're going to see if there are any AC amps in the water. Turn off all the boat's AC breakers. The meter's leads will be in the same places as the last test, but set the meter to AC amps. The resulting value should be no more than a fraction of an amp. If more, the problem is either defective dock wiring or in a neighboring boat.

8a. This test confirms that there is no connection between shipboard AC grounding and AC neutral lines. With all breakers off and shore-power disconnected, put the meter in its lowest ohms range and measure between the panels AC grounding and AC neutral bus bars. There should be infinite resistance.

8b. Like test 8a but with the main breaker on. Again there should be infinite resistance.

8c. Like tests 8a and 8b but watch the meter as the boat's circuit breakers are turned on one after the other. In each case there should be infinite resistance.

8d. For boats with two 30A shorepower feeds, the neutral lines should be isolated from each other. Test this by putting the meter in its lowest ohm reading and measuring across the two neutrals. The value should be infinite—i.e. and open circuit.

8e. Finally confirm that the shipboard ground and hot lines are isolated from each other. With all breakers on and shore-power disonnected, put the meter in its lowest ohms range and measure between the hot and ground on any shipboard outlet. The value should be inifinite.


credit: Nigel Calder

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