Electric Shock Drowning

Recently, I attended a presentation which was sponsored by ABYC (American Boat and Yacht Council), entitled ESD (Electric Shock Drowning). The seminar was presented by Kevin Ritz, a highly qualified expert in marine electrical systems.

I have put together some of my own thoughts along with Kevin’s to share with you, regarding this silent killer; Electric Shock Drowning (ESD).

ESD is a phenomenon which many times goes un-recognized in many accidents which occur around water, and marinas. So often an accident victim is pronounced “dead-by-drowning” when in reality, there was no drowning at all. ESD doesn’t always present itself as an electrocution on dry land, with burning of the flesh, due to the victim being in water. Many times there are no clues at all. The reality is it requires a very small amount of electrical current to induce muscle paralysis, which can stop the heart.

Boats, irrigation pumps, fountain pumps and other equipment which are connected to a source of land-based power, are potential threats to a swimmer. Technology is available to greatly reduce the threat. But, in the event of a breakdown in the system, an electrical current flow can begin passing through the water.


Let’s use a boat in the marina as our example:

Aboard the boat, the basic 30 amp/120volt AC shore power receptacle is (or should be) wired with three wires; Black/Hot, White/Neutral, and Green/Ground. Many times a non-electrician will refer to the white wire as a “Ground”. But in reality, it should be referred to as a “Current-Carrying Neutral”. The Green wire is a “Safety-Ground”.

When working as designed, an appliance or piece of AC electrical equipment on the boat will work just fine, with only a Black/Hot and White/Neutral connection. The Green wire is often neglected by the amateur electrician, as a nuisance, and is not always installed properly. Electrical current enters the boat on the Black wire, passes through the appliance (load) such as a water heater, or battery charger, and then returns to the shore power supply; all is good. (always wants to return to the source.) The Green wire appears to have done nothing in this scenario, except take up space in the electrical panel.

The Green Wire (Safety Ground) is (or should be) connected to all cabinetry and frames of the on-board electrical equipment. is also supposed to be connected to the “Bonding” system if one is installed. A Bonding system ties all of the under water through hull equipment together electrically, to reduce corrosion; that’s another topic we can discuss later.

But, what if we have a failure in a piece of 120 volt AC equipment, or wiring, that provides an electrical path for current to bypass the normal White Wire return to the marina supply ? Imagine the failure of a 12 volt battery charger, which puts 120 volts AC, on the DC ground wire, which connects to the engine block, prop shaft etc. Or, what if the water heater fails, and puts AC voltage onto the metal cabinet frame, which is Green wire connected to all of the thru-hull fittings……… Etc…. Etc….. The “What-If’s” can go on and on. But wait. There is good news. We have a Green Wire Safety Ground. The Green Wire will join into the circuit, and low resistance path for the leakage current back to the shore power post. All is good.

But, what if there is a failure in the Green Wire Safety Ground. Or, what if the weekend do-it-yourselfer, didn’t install a Green Wire ? In this scenario, we have AC current, returning back to the marina’s supply, not only on the White wire, but now through the prop shaft, and thru hull fittings into the water and down to Mother Earth, or possibly to another neighboring boat with a Bonding System and a good Green Wire Ground.

THERE IS NOW ELECTRICITY IN THE WATER. And worse yet, everything might still be working on the boats, and nobody even suspects a problem. In a perfect world, we have some control over the environment. But, the fact remains: We don’t know what’s inside our neighbor’s boat.

Although this problem exists in ALL waters, this is more of a PROBLEM in FRESH WATER environments. Why is that ? We all know that salt water conducts electricity better than fresh water. We learned that in high school, and it’s true. But, what we are over-looking is the conductivity characteristics of the human body. We as humans, have the same conductivity as ocean salt water. (It varies from person-to-person.) But in almost all cases, we are better conductors of electricity, than is fresh water in the lakes and rivers.

Now, let’s go back to the boat. Let’s say we have a boat putting AC electricity into the harbor. If we probe the water with a volt meter, we will see the areas closest to the boat will read a higher voltage in relation to shore power ground, than areas further away. This can be drawn on a piece of paper, like the bull’s eye of an archery target, with the offending boat as the eye of the target. Each ring of the target will read less voltage than it’s neighboring ring which is closer to the eye. The diminishing values in adjacent rings of the “target” are called the “Voltage Gradient” or the voltage difference between one ring and it’s neighbor.

The US Coast Guard has done studies on this phenomenon and have determined that a “Voltage Gradient” of 2 volts AC, over 1 foot of distance (2v/ft) is enough to cause 12 milliamps of AC current to pass through the human body. That’s .012 amps.

Remember ? We humans conduct electricity better than the fresh water. A human body in the field of electrically charged fresh water becomes the path of least resistance for current to flow. We don’t even have to touch bottom…… or the dock ! (either of which could increase the problem for the swimmer) Suddenly the human body can become an easy conduit for current to flow.


12 milliamps (ma) of electrical current is enough to induce muscle paralysis – “can’t let go, or release your grip“. At 18 to 22 ma, the diaphragm contracts and you can’t breathe. At 50 to 65 ma we experience heart fibrillation, and at 100 ma (1/10th of an amp) death.

This is not an uncommon accident. In 2012 so far, there have been 7 fatalities which can be directly attributed to ESD. And, another 15 which are questionable, and most likely related to the same problem. As I said earlier: It’s often “mis-diagnosed”.

So, what should we do ? How can we check our boats ? What if we see a swimmer in the harbor having a problem ?

I’ll start off by simply saying: Don’t get in the water in a harbor….. Period.

A quick check of the boat can be accomplished with a “clamp-on” amp meter on the shore power cord. It should read zero (0). All current entering the boat, should leave the boat on the same cable; hopefully all on the White Wire. Current flow in cancels current flow out on the meter. It should read zero. If the meter reads something above zero (0), then some of the current is leaving the boat another way; probably through the water. This test should be taken with all of the appliances running; can be one appliance at a time, but test with each one operating. It’s no guarantee, but it’s a good place to start. Beyond this simple test, you should probably get a qualified marine electrician involved.


Dead fish and birds in the water. Excessive corrosion and rapid loss of zincs on the boats. Boats operating with an extension cord, instead of a marine shore power cord, should be suspect.

Use marine grade battery chargers and appliances. National Electric Code (NEC) specifies that the White and Green wires are tied together within the fuse box at the main electrical panel, in dry land installations. This is NOT the case on mobile vehicles, such as RVs and boats. Never tie the White and Green together aboard the boat or RV. The Green Wire Safety Ground should go all the way back to the source (dock supply post), before connecting to the Neutral White. Many non-marine type small appliances, such as small refrigerators will have a jumper wire in the power supply which ties the White and Green together. These “jumpers” are supposed to be labeled so as to be removed if installed in a mobile vehicle.

If you see a swimmer in trouble: Our first instinct is to dive in and help. BEWARE ! He may be getting an electrical shock. If you dive in to help, you too will suffer the same fate. Get the power turned off ASAP on nearby boats and if possible to the entire harbor. Watch for tingling sensations in the water. If present, stay out ! Warn first responders. They may not be familiar with electricity over water environments.

There are devices on the market which can help. One such device is an isolation transformer. The transformer eliminates the physical connection of the boat, to the shore power post. With an isolation transformer, the boat becomes the original source of power. As I said earlier: the electric current will always try to return to the source. So, instead of radiating through the water, in an attempt to return to Earth ground, the fault will stay aboard the boat. There are still dangers aboard the boat, but the current will not try to flow through water in the harbor.

Ground Fault breakers and outlets will help. A ground fault circuit interrupter (GFCI) will monitor the ebb and flow of current on the white and black wires, and “trip” if the two don’t match. The theory here is if it’s not all coming back where it’s supposed to, then it’s leaking somewhere else. In December of 2013, the boat manufacturers will be required to install an ELCI on all boats before they leave the factory. The ELCI will be installed in the main electrical panel of a boat, and monitor the IN/OUT flow of current, as described above in the GFCI. Meanwhile, we still have a whole bunch of boats out there, without protection.



Ron Smith


Accredited Marine Surveyor #459

SAMS (Society of Accredited Marine Surveyors)

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