I have made this point before, but I want to start right off with it again. Electrical work on your boat should be, at the very least, supervised or inspected by a qualified marine electrician. ABYC offers a very thorough certification course in marine electrical. I have taken it and hold the certification. But, I do not put my skills and experience in the same class as a certified technician who performs installations and repairs every day. As a generalist, it is important to recognize the specialists.

BoatUS puts sinkings and fires as two of the top three causes of marine casualty (the other of the top 3 is SSO…struck submerged object, FYI). In many cases, both can be tied back to the electrical systems. About half of the sinking cases I have worked had either a primary or secondary link to the electrical system. Most of those cases, had a failure or fault caused by the do it yourself electrician. You might also be surprised to hear that several of those cases were boat owners who were professional residential and /or commercial electricians.

Boat are unique vehicles in that most have both DC (direct current) systems and AC (alternating current) systems. They share this unique characteristic with campers / RV’s, but have the added complication of resting and operating in the water. I will be scolded by the true electrician’s out there, but it could be said that a marine vessel operates in an electrolytic solution. Being careful not to tip over into the depths of a science article, simply put, this is a solution which can do many things including being capable of conducting electricity.

To dispel a common myth, water is a poor conductor of electricity. That is, purified water / distilled water, is not very good a conducting electricity. It is all the little things (and some big things) in water that give it the ability to conduct electricity. If your vessel operates and slips in brackish or salt water, you are very aware of how boat maintenance compares to a camper.

Books have been written about marine electrical. I confess I struggle with making a brief article on the subject that is anything more than a dangerously incomplete account. But I’ll defer again to paragraph number one above. Following, I’ll endeavor to point out some failure modes and the systems they are usually associated with. The hope would be that understanding the dangers, causes, and associated systems might compel you to take a closer look. Or hire a technician or inspector to give your electrical systems a once over.

Direct current or DC systems, 12 / 24 / 36 volt, generally start at your battery banks. There are many types of batteries, all of which require maintenance, even those that say “maintenance free.” The “maintenance free” battery is usually sealed and does not require that you add electrolyte. However, keeping the posts and the connecting conductors clean reduces resistance, extends battery life, and prevents heat related damage to your DC systems. Look for batteries which are bulging, or are discolored. Commonly, overheat conditions to a battery will express brown or black discoloring, particularly around posts  / studs or on the top of the battery.

Most of your ships systems are operated by DC current from your engines and batteries. Unless you have a generator or inverter, every system you need on the water is DC powered. Even your gasoline or diesel powered engines will not operate if your DC electrical system has a major breakdown.

DC electrical is the cause stray current corrosion. Stray DC current can eat a lower unit, prop shaft (see picture. This was from a fresh water boat), or other metal components, in a matter of a few days. Stray current is generally fault current from a DC device or improperly grounded (improperly wired) conductor.


Alternating current or 120 / 240 volt AC systems, generally consist of shore power or onboard generator systems. It can also include inverted DC current if you have an inverter system. It would not be prudent to understate dangers of DC current, but it is hard to overstate the dangers of AC current. We take it for granted since we use it every day, all day, in our homes and offices. Simple safety mechanisms are built in to protect us on land. It becomes more complicated on water and the methods for properly wiring AC on a boat have a deadly distinction. Improperly wired, they can kill.

This hazard level should dictate providing a comprehensive list of systems and deficiencies. But again, books have been written, systems are many, and this is a blog article. Lets keep to a few key points.

Is the wire you are looking at a conductor of AC or DC current. AC current, at 120 volts (typical of most systems), is deadly at 25 milliamps. That is .25 amps (yes the decimal point is in the right place). Your coffee maker draws about 3 – 4 amps with the heater and hot pad on. That is at least 12 times the necessary amperage to kill you. Point being, before you start working on your electrical system, make sure you know what you are grabbing.

GFCI outlets should be located in every “wet” area. These include the galley, head and any areas of the vessel which are weather exposed. Most AC electrical systems on boats built today have all outlets linked to a GFCI outlet. Test them every year because they do fail, regularly.

Wire nuts are an inexcusable carryover from the land-based electrical toolbox. First, they are suitable for use only on single strand wire, which is not rated for marine use. Multi-strand wire is less prone to flex and vibration failures. Wire nuts damage multi-strand wire and do not provide a reliable junction, no matter how much electrical tape you put on them. I can attribute fires, sinkings, and shocks to wire nuts on boats. It is only a matter of time before I see a fatality associated with them and I am sure another inspector out there already has.


There are many more common hazards associated with these systems. But, this is about what you can do to get to know your boat. It is not my intention to scare you away from knowing your electrical system. On the contrary, take it seriously and get to know it. Shut off all the power systems. Properly disconnect all batteries and disconnect chargers / shore power systems. If you have an inverter, including a  solar inverter, be aware that they have capacitors which store a good jolt of current. Follow the user’s manual for service procedures to discharge capacitors before picking around these systems.

Now climb down in your bilge and start tracing wires. See what they are for and where they go. The conductor (wire) should be marine grade (stamped on the wire), secure every 18″, have safe distance from heat sources (engine manifolds, exhaust, genset, etc.), and be chafe protected at pass through locations (bulkheads, frames, decks). Look for loose or broken connections, discolored wire, damaged wire jackets, and loose or exposed ends.

Take a course and read some books on marine electrical if you want to take on projects, or hire a certified professional for repairs, installs, or upgrades. You may even be able to carry the bag and help your technician to save some time (money) and learn the system. Not always an option, but you can ask.

Getting to know what your electrical system consists of, and identifying problems will save time and money, as well as give you some peace of mind knowing that things are in order below decks. If they are not, you’ll know better what to look for and where to look.