[SIKSUKR]

Your house has a 3-wire system using one wire to ground to the earth under your house to carry the energy away from you and allow it to discharge into the ground protecting you from electrocution.

Your boat doesn't sit on the ground or earth--it floats, so you cannot run a ground wire to the earth under the boat.

The 12V system (2-wire) on the boat grounds back to the battery. The negative terminal on the battery is connected to a grounding cable connecting all the metal surfaces on the hull. This bonding system equalizes potential current between the fittings elliminating any potential difference in voltage between the fittings. This not only protects you from electric shock, it also helps reduce corrosion.

110V Shore Power or Generator Power is a totally separate, independent wiring system. It is a 3-wire system that is grounded back to shore, or the generator.

When Something Goes Wrong

When an uninsulated part of a 110V (hot) live wire comes in contact with an uninsulated part of a 12V wire, the uninsulated 110V then uses the 12V ground, making all the metal parts on the bottom of the boat live with 110V. Because fresh water is a poor conductor, it forms a gradient around the boat. If a person enters this gradient while swimming, the current will flow through the body causing paralysis or ventricular fibrillation and death because the the human body is a better conductor than fresh water.

A parallel we've all heard about is a car becoming electrified when live hydro wires fall and touch the metal of the car. The rubber tires insulate if from ground. When a person standing on the ground touches the vehicle, the current passes through the body to get to ground, electrocuting the person. The human body is a better conductor than rubber, air or water.

It's no different on the boat. When a person enters the gradient around the boat, the current passes through the body to get to ground and the person dies from electric shock. The only difference is that there is no burn mark on the victim in the water and the death is usually labelled as drowning.

What Causes a Fault?

Faults causing this gradient can occur from frayed, corroded or faulty wiring, poorly installed or non-marine appliances (marine and onshore residential electrical standards and safety requirements have some very important differences). It could be caused by a current leak from electrical components such as pumps, refrigerators or battery chargers or a non-approved receptacle. It could also be caused by hull movement chaffing or rats or other animals chewing wires. Using automotive-type battery chargers or running appliances on domestic 2-wire extension cords could also cause a fault. It could also be caused by reverse polarity if the wiring on the dock or the wiring in the boat or an appliance has black and white wires reversed. If a domestic appliance with two prongs is used, there is no ground and it's a 50% chance that it can get plugged in the wrong way.

You will read in Kevin Ritz's story that a random sampling of 50 boats in three freshwater marinas in the Portland area found 26% had faulty wiring. So, even if you have had your boat checked, you have to be aware of all the other boats around you as well.

Stray Current is Destructive and Dangerous

I was alarmed that such a high percentage of boats had faulty wiring; but, I spoke with local marine technicians who agreed with the finding and shared some of their stories. There are too many to print, but I can share a few with you.

One technician told me of a boat that had its prop and outdrive eaten off by electrolysis (in just three weeks) from current leaking into the water. It took him some time to find the problem, but he found that the boat owner had put a screw into a bulkhead and unknowingly screwed through a 110V wire causing it to ground to the 12V system. The 110V went straight to the 12V grounding system into the water and destroyed his props and drives. If he had jumped into the water around his boat, he would probably have died from electric shock--all because of one misplaced screw.

Another case was a woman who complained about her legs and feet tingling when she put them into the water from the platform. The marine technician pulled the Shore Cord (laying in the water between the dock receptacle and the boat) and the tingling stopped. It turns out the shore cord was old and dried and cracked and there was leakage of the 110V current directly into the water.

Apparently, marine technicians are constantly finding wires improperly joined and uninsulated--just twisted together. The movement of the boat can shift the wires and cause a fault, resulting in current leakage into the water.

For NoBozo:

One boat owner had severely corroded props and drives and when the marine technician investigated, he found that the sailboat next to him had faulty wiring and there was a gradient around the sailboat from the 110V leakage that was enough to destroy the props and drives on the boats on both sides as well as damage to his underwater gear.