Electrical System Use and Maintenance
by David H. Pascoe, Marine surveyor
If you've owned a boat for any length of time, you probably know that insurance companies hire independent marine surveyors to conduct insurance surveys on the boats that they insure. One of the most common problems that surveyors run across in doing these surveys are electrical systems that have either been jury-rigged by the owner, or an owner who hired Joe-the-Electrician down the street because Joe's work is cheap. Joe is the guy who knows how to wire a house and thinks that boats are no different. The house business isn't so good, so he switched to boats.
By the time a boat gets a few years on it, the amount of substandard and/or jury-rigged wiring on it can add up to substantial numbers of faults. Much to the consternation of the owner, when the insurance surveyor comes along, he ends up handing the owner a long, and frequently costly, list of things that need to be corrected. Even more seriously though, is what substandard wiring can do to your overall system, not the least of which are chronic battery drain, frequent system faults, or even causing electrolysis and fires. In the last month alone, I caught two boats that were about to go up in flames, and one that actually did catch fire during the course of a survey. One because the owner had installed air conditioning controls below a companionway hatch that got wet and shorted out, the other due to an improperly wired service outlet.
Let's begin with the fact that a boat is not a house or a car, simply because the later two don't float in water, which is what makes a boat inherently different. Especially a boat that floats in sea water because sea water is a fair conductor of electricity. Therefore, there are lots of additional rules about the materials and methods of installation that you won't find on land based vehicles or structures. Because water (both inside and outside the boat) provides a very convenient ground path for electricity, we have to be a lot more careful how we do things.
There are no schools for boat electricians, only ship electrical engineers, except for the occasional vocational school. Most marine electricians are basically self-educated by means of attending seminars and the like. When hiring an electrician, you should not take their word for it because it says so in the ad, or your friend said Joe was really cheap. The least you can do is ask for a resume, since long experience is probably the best criteria.
Materials & Equipment
It is important that only equipment and materials rated for marine application should be used. The American Boat and Yacht Council (ABYC) has very stringent standards for this, as does Underwriter's Laboratories. This means things like common wire and wiring devices, as well as electrical equipment, should not be used. That non-marine fan, airconditioner or battery charger, because the electrical apparatus is not properly constructed, insulated or grounded could either start a fire, or worse, result in an electrocution. Federal regulations require that all electrical devices used in the engine compartment or bilges be "ignition protected" meaning they won't create sparks that can cause a fire or explosion.
One of the worst offenses we see on boats is the use of extension cords and other non marine wire, even such things as audio speaker wire and household lamp cord on high voltage systems. No, I'm not kidding. speaker wire carrying 125 volts. You should never use household wiring devices, such as multiple outlet expanders, or wire. Purchase electrical supplies only from a reputable marine supplier. Wire must have the proper temperature, water and oil resistant ratings and is hard to come by at retail outlets.
This service outlet was replaced by some one who didn't understand high voltage wiring and this is the result. The breaker was very old and the contacts fused closed and would no longer trip. This photo was taken during a survey while the wood behind the panel was burning. The owner showed no concern about it, thought it wasn't serious.
Here's a good reason why this ribbed plastic conduit should not be used on boats. Not only is it highly flammable, but it spreads the fire.
High Voltage Systems
No one who is not trained in marine high voltage systems should ever perform wiring on a boat. The potential for creating deadly system faults that are injurious to both people and the vessel itself is too risky. That includes something as apparently simple as wiring a new service outlet, for if you don't understand the principles of the system, you are likely to unknowingly create a problem. Just because you know how to do wiring around the house, doesn't mean you know what you're doing on a boat.
Grounds and Grounding
One of the least understood aspects of a boats electrical system, and the most troublesome, is the proper method of grounding. That we often get questions of whether AC or DC electrical equipment should be grounded to the boat's bonding system is illustrative of this point. AC and DC grounding systems are two separate systems, for distinctly different reasons. If you don't understand these systems, you run the distinct risk of creating a disaster. Actually, there are four separate ground systems: DC ground, AC ground, AC grounding (or bond), and the vessel's bonding system. You can add to this lightning and HF radio grounds as well. Do you know the principles of each? Are you sufficiently confused to discourage you from doing your own wiring? I hope so. For unless you understand each thoroughly, you're headed for trouble.
The AC ground and grounding systems are "free floating," meaning that they do not ground on the vessel, but only to shore. The ground, or neutral, is a current carrying conductor, and is the source of many troubles because people do not regard it as such. The grounding, bond or green wire is the "safety" intended to channel current safely to ground in the event of a short circuit. Both of these circuits are capable of conducting current and can be the source of electrolysis when there are system faults with the dock or marina wiring. This is very easy to test for.
There is only one point where the DC side is grounded, and that is at the battery. It, too, is a "free floating" system in which nothing is ever grounded to any metallic part of the vessel, most especially not the bonding system. Just like a car sitting on rubber tires, completely insulated from earth potential, the battery itself provides the negative potential.
The bonding system, also green wire, has nothing to do with electrical systems. Underwater metals are simply wired together to equalize differences in potential of different kinds of metal. Nothing should ever be grounded to the bonding system. Unfortunately, some people don't understand this and use it to ground electrical equipment, occasionally with disastrous results.
Bonding simply means wiring all the boats underwater metals together. This is done because of the galvanism caused by the different metals. By wiring them together, the differing potentials are equalized. Bonding does not solve problems of galvanism or electrolysis, but it does spread the the flow of current around over more metal, so that 1/4 volt or so won't cause any damage. Whereas if that 1/4 volt were going to one small seacock, it would probably eat it up in a hurry. In other words, bonding lessens the effect of small amounts of current. On the other hand, it also spreads it around to all underwater metals so that higher currents end up damaging everything.
Bonding systems use wire and ordinary crimped ring terminals. After a while these get wet and corroded. Electricity doesn't flow very well through corroded metal, so your bonding system after a while stops working. To maintain it, simply cut off the old terminals and install new ones. Do you have wires attached to sea cocks with hose clamps? Forget it. This is putting stainless and copper together, which are galvanically incompatible and it won't work.
Your Bottom Paint
What does bottom paint have to do with electrical systems? Nowadays, with copper based paints, a lot. If, the next time your boat is hauled and you see large ugly burn patterns around all your underwater metals, you got a stray current problem. Copper-based bottom paints react severely to stray current, and serves as a great indicator. Sort of litmus paper for electrical problems.
Of course, the common wisdom is that the stray current "is from the marina." Or it's always the other guy's boat that is causing your problem. Don't bet on it. Most stray current problems are sourced on the boat in which they appear. Otherwise, everybody in the marina would have the same problem.
Electrolysis and Galvanism
Electrolysis is a word that is badly abused by boaters who don't really know what it means, so let me correct this right now. First, understand that all boats have an electrical potential. That's because of all the different metals on the boat which, themselves have differing electrical potentials. This is exactly the same principle that makes a dry cell battery generate electricity. This electrical potential is called galvanism and is the reason why we put zincs on boats.
Electrolysis is stray current escaping from the system and is most damaging. It is an abnormal condition. When this happens, it will eat up the zincs in no time, usually leaving that metal looking bright and shiny. Therefore: Shiny zincs = electrolysis. Dull eroded zincs = galvanism.
I spent two years putting a meter on every boat that was hauled for survey. The average boat generates about 1/4 volt DC current and going as high as 1/3 volt without causing damage. But when it gets up to 1/2 volt, you got a problem. Zincs will erode rapidly and underwater metals begin to be affected.
Shore Power Cords
The single largest cause of problems with shore power systems results from failure to maintain the connectors on both the cord and the boat connectors. These devices are exposed to water and over time suffer from corrosion and general wear. High resistance caused by corroded, bent or worn connectors results in high resistance which causes overheating, which further amplifies the power drop. This not only creates conditions for a potential fire, but causes electrical equipment to work harder, resulting in reduced life span of equipment. IT PAYS TO MAINTAIN SHORE POWER CONNECTIONS.
You can perform a very simple check just by placing your hand on the shore cord near the connection to determine if it is heating up. Obviously, this should be done while you have a lot of equipment turned on. If it's anything but slightly warm, not more than 110 degrees, suspect a problem. Shore power connectors should be dismantled at least once per year, cleaned and repaired as necessary. Most of these connectors have replaceable parts. If you drop your shorepower connector in the water, you must take it apart, clean and dry it. Otherwise, expect it to burn up.
We recommend that you buy only the highest quality power cords, as these will last longer and have the advantage of replaceable connector parts. Cheap connectors usually can't be taken apart. We also advise against ever using the three-pronger household type adapters as this type of connector is highly unreliable and prone to causing system faults and fires. Only the twist-lock type connector is suitable.
One more thing: If you are not turning off the dock breaker before disconnecting the power cord, start doing it now. Not only do you risk getting electrocuted, but disconnecting an energized connector damages the contacts. Also consider what happens if you drop the energized cord in the drink!
This is an issue only with 125 VAC systems since 250 VAC systems will not function with wrong polarity. Since you have three terminals on a shore connection, wrong polarity can mean that any of these wires are in the wrong position. Not only should you pay attention to the polarity indicator on your boat, we recommend that you keep a plug in polarity indicator aboard and use it every time you hook up to shore power at a different location.
Reverse polarity is not only an electrocution hazard, but can also damage electrical equipment. It is most often found with the three prong spade connectors (household type), but occasionally twist lock connectors as well, particularly in marinas with dilapidated equipment. Never trust the power supply at strange docks, but always check the polarity. When hooking up to strange docks, always check your volt meters to make sure you have adequate voltage. Low voltage is very damaging to electrical equipment. Turn on the stove or water heater and watch what happens to the meter.
Main Circuit Protection
Many people think that the circuit breakers on the dock protect their boat. They do not; they only protect the dock wiring. Your main circuit breaker protects your boat's systems. But what about that section of wiring and connectors between your main panel and the dock breaker? Well, the fact is that it is unprotected. which is why so many fires occur. Check out all the top end boats and you will find that they have circuit protection located directly at the shore connectors. Which is why we recommend that you should too. Having slow blow cartridge fuses installed directly at the connectors can go a long way toward preventing fires and burned up shore cords, particularly if you are a traveler and frequently rely on uncertain power supplies. Circuit breakers should NEVER be installed on the exterior of the boat. Only gasketed, water proof cartridge holders should be used.
Circuit breakers wear out, and when they do they work less well, or not at all. If you are using circuit breakers as ON/OFF switches, you are helping them wear out that much faster. It also damages breakers when you shut off equipment via the breaker. This causes arcing at the contact points which damages the points. When connecting and disconnecting shore power, you should always turn OFF equipment at the appropriate switch on the equipment. Then shut the main breaker off. Do not ever simply throw the main breaker off to shut down equipment that is operating. The circuit breaker arcs and damages it.
Also be aware that any equipment run by a motor, such as air conditioning and refrigeration equipment, start up with an initially much higher amperage than the normal running amperage. An air conditioner that runs at 14 amps may have a start up amperage of 20 amps, so that if you just go and turn all the equipment on at once, it overloads the system. Then the circuit breaker gets hot and won't stay engaged until it cools down. Ergo, start up heavy equipment one item at a time, allowing it time to cycle into its normal operating voltage before turning something else on. For example, don't turn the AC, refrigerator and icemaker all on at once and not expect the breaker to pop.
Chronic Breaker Popping
It's human nature that when a problem appears, we wish it to go away. Breakers that pop frequently are signaling that there is a problem, which could either be the breaker, or something in the circuit. Yet most people will keep on attempting to make the breaker engage. This can be dangerous because you may cause the contact points of the breaker to fuse together from arcing, in which case it will never trip again. The above photo shows what can happen when you do this. DO NOT ATTEMPT TO ENGAGE A BREAKER THAT IS OVERHEATED BY FORCING IT. You must allow it to cool down.
If you are experiencing chronic problems with circuit breakers popping, first check how much current draw is involved. A single 30 amp circuit is not much when you're running things like air conditioners, water heaters and battery chargers. One very simple way to check whether you're dealing with an overload problem is to add up the amperage draw of each piece of equipment. List both the start up and run amperages. You will usually find the amperage given right on the equipment label. By making a list of the total power demand, you'll get a good idea of what you can and cannot operate simultaneously, particularly when starting the equipment. If you have an ammeter on your panel, check it against the amperage tally you made. Ideally, you should try to hold power consumption at 80% or less than the line rating.
Check the breaker by allowing it one hour (or whatever it takes) to cool down. Turn the equipment off and, after it is cool, reengage the breaker. Now turn the equipment back on. Place your finger on the front of the breaker and note its temperature. If it does not heat back up again, then the problem was probably a start-up overload. If the temperature rises again, there is a fault in the circuit or the breaker. (Note: when the breaker contact points become eroded, the breaker itself can overheat).
Ground fault current interrupter service outlets are required to be installed in wet locations such as the galley or head. In reality, there's little chance of being electrocuted inside a boat because you are not grounded within the boat. A greater risk is from service outlets being located in places that get wet, such as below leaking windows, hatches or close to doors. Three pronged plugs are prone to shorting across the terminals when wet, so having all your service outlets changed to GFCI's is a good idea. Use only the highest quality devices from a reliable manufacturer like GE, and not the el cheapos from the local discount store. They aren't worth having. Service outlets located anywhere on the exterior of the vessel are an invitation to trouble for reasons that should be obvious.
The same advice about jury-rigging wiring applies to DC systems as well AC systems. While you're not going to create an electrocution hazard, it is very easy to take a faultless system and create faults in it. A typical problem starts like this: The owner wants to add a new piece of equipment, but the electric panel is way over there, and the place he wants to install the equipment is way over here. Besides, there are no extra breakers in the panel, and no space in the panel to add another one. To make matters worse, the panel is located in such a way that he couldn't string new wires into it even if he wanted to. So what he does is to find a place where he can tap off an existing circuit, and maybe adds an in-line fuse, stringing wires all over the place in the process. Or maybe he is replacing a piece of equipment that has a faulty circuit, but instead of trying to locate the fault, he just clips off the old wires and strings new ones. This happens a lot, and by the time the boat has a few years on it, it's got cut wires all over the place, many of which are still hot!
In many cases, he will just go and take new leads off the batteries, bypassing the panel altogether. Now when he goes to turn off the main power supply, all that new stuff added remains energized. In addition to which in-line fuses have also been added all over the place, so when something craps out he's got to go tearing through the boat to find that hidden fuse.
If you have electrical problems and your system looks something like this, then you needn't look much farther for the source of the problem<
Not every electrical system is going to be this neat, but this is the way it should be.
The worst of the problems with DC system add-ons comes with improperly installed wiring and the use of wire splices of all sorts. Typical of these are the use of electrical taped connections which, when the tape gets warm (as in the engine room) the tape glue gets soft and the tape falls off. Or the use of wire nuts or crimped butt connectors in locations that get wet. Wire nuts (those twist-on cones) are not approved for marine use. When connections get wet, the wire corrodes, creates high resistance, usually resulting in equipment damage or failure for reasons which the owner will never discover. He'll think just that damned lousy piece of equipment crapped out, when in fact the lousy wiring job is the culprit.
Principles of Wiring
I would venture to say that half the electrical problems on boats result from improperly installed wiring. After the boat is built, there's no convenient way to route new wiring. But we need to understand that systems on boats are subject to high G-forces due to pounding, rolling and vibration. Connections get stressed and wires rub and chafe against abrasive or sharp objects. It doesn't take much damage to wire insulation before you have a condition where stray current may develop. And the chance of finding a little bit of damage on one wire is about nil.
1. Must be routed in a suitable, dry area and be well secured. Should not be laying in bilge or in areas that get wet.
2. Must not be routed with pipes or hoses of any kind, and not be in contact with fuel tanks or fuel lines.
3. Splicing circuits should be avoided. If splicing is necessary, it should employ a proper terminal block, and not butt connectors (see above photo). Every splice in a circuit creates additional resistance, and the potential for the connection to come apart. Taped connections and wire nuts should not be used.
4. Wiring must be firmly secured and in locations where it won't get damaged. Should not be dangling or strung across open spaces. Use only plastic, not metal, clips to secure the wiring.
5. Must have chafing protection or conduit at vibration points around machinery.
6. Must not be in contact with, or proximity to machinery exhaust systems.
7. Wiring should be neat. A boat full of tangled wiring demonstrates unprofessionalism and the inability to fix something that goes wrong. An electrician can't trace a plate of spaghetti, and when something does go wrong, the cost of fixing it goes way up.
Adding in-line fuses to a newly installed piece of equipment is a terrible way to add circuit protection. First of all, these devices trap water and corrode internally. Secondly, you end up with two more splices in a wire circuit that shouldn't have any. Third, you usually forget where they're located, and if you've got ten of them on your boat . . . well, you get the picture. Jury-rigged systems are just that; a temporary, unreliable system. A boat full of in-line fuses is a boat full of short cuts and amateur installations.
Batteries are a constant source of aggravation to many boat owners, almost always for reasons that are preventable. These are: low quality batteries, poor or non existent maintenance, and improper installation and wiring.
As a general rule, batteries perform consistent with the price you pay for them. Good batteries are expensive, and shopping for price will only lead to momentary satisfaction. Cheap batteries have thin plates and poorly insulated casings and therefore cannot give long service.
This illustrates why crimp-on ring terminals, wing nuts and other substandard high amperage cable connectors should never be used. High resistance has melted the cable insulation and burned up a $900 starting motor because of high resistance.
Secondly, batteries have to be installed correctly. That means in a clean, dry location that can be reached. If you can't reach them, if you have to kill yourself to get at them, then you will not maintain them. If installed in an inaccessible location, you should consider having them moved to a better location.
Place a fully charged battery on the concrete floor of your garage. Then come back two weeks later and check the charge. That battery will have completely discharged, and it will have done so right through the plastic casing. Now you understand my point about proper installation and dryness. On many small boats, I usually find the batteries sitting in uncovered plastic boxes that are full of water. Or they're sitting in bilge water or on wet decks. If that's the case, you needn't look any farther for at least part of your problem. If you want your batteries to be reliable, they must be kept clean and dry. That includes the top surface, particularly between the terminals.
It won't do to make your cable connections with threaded studs and wing nuts. These afford inadequate contact surface that can cause high resistance and is one of the major causes of engine starting motors burning out. Your starting motor cables should be attached only with swaged lead lugs, not the ring terminal kind smashed with a hammer to make the connection. Small boats are usually the worst offenders in this regard.
Corrosion takes its toll even on the interior of the boat due to leaks, salt air and high humidity. When tested, most of these connections had high resistance. This is the proper method to splice wires.
Batteries develop heat when charging, as well as hydrogen gas. For that reason, the need to be in a well ventilated area. Gel cells are particularly vulnerable to overheating damage. Putting gel cells in covered, plastic boxes has proved to be a problem, and for this reason they are falling out of favor. Sometimes improved technology isn't an improvement after all.
Electrical Devices Exposed to
Why it is that there so many builders that install instruments, panels and switches in locations that are going to get wet is something I'll never understand. Oh, I know, you look at those switches and think that they're water proof. Well, you just go look at the back side of the panel and see if you still think so. See if you don't see a lot of corrosion back there. What happens when the back side gets wet? Well, water being a conductor means that these devices will short small amounts of current across the terminals, or to any available ground. This is one of the reasons why you have so many engine instrument failures, and boats have so much of a hardware corrosion problem, and why they have stray current problems, never mind equipment failures. Electrical equipment exposed to weather that is not absolutely water proof is just asking for trouble.
Locating Internal Equipment
Just because it's inside the boat doesn't mean that electrical equipment will stay dry. Boats leak, and stuff located under those leaks are going to get wet. That means that you have to pay attention to where you put stuff. Many people mount various types of pumps low in the bilge, assuming that the bilge water is never going to rise. Believe me, the bottom of the boat is the last place you ever want to mount something. Sooner or later your bilge pump will fail, and when it does that expensive equipment is going to get ruined.
The other place you never want to mount anything is under an open cockpit deck. For reasons I won't get into here, this is a terribly wet environment, which is why boats with generators located here end up replacing generators a lot.
If you have exposed panels you need to keep them covered and dry. The vast majority of small boats that I see don't even have panel covers, yet alone having covers that are used. Having a small cover made up is a small price to pay to avoid serious damage and other problems.
Looking at this ball of wiring hanging down, is it any wonder that a lot of electrical equipment on this boat didn't work? Instrument panel of this open boat was not kept covered. Water pouring through the panel had even filled up the battery boxes with water.
Close up of wire bundle at left. These supposedly water proof wire connectors, on closer examination, are found to be full of water.
Due to vibration and high temperatures, damaged wiring on and around engines is one of the most common causes of stray current damage, i.e. true electrolysis. It is extremely important to consider the routing of the wiring so that it is not in contact with hot manifolds, or vibrating on sharp edges or rough surfaces. Engine wiring should be inspected periodically for signs of damage.
Avoid using the kind of highly flammable plastic conduit shown above. If you are painting the engine, do not paint the wires; the solvents in the paint causes the insulation to become brittle and crack.
The Effects of Time
Electrical systems don't last forever. Over time boat systems degrade, particular as respects to the effects of corrosion. We recommend that a boat should have an electrical system survey once every 5 years. This does not take long and does not cost much, and can save you thousands of dollars in unwelcome headaches. In most cases, the survey will simply reveal the effects of corrosion which needs to be cleaned up, along with few possible minor repairs. The advantage is in not allowing problems to accumulate to the point that it becomes a big, costly job.
A Word About Buying Older Boats
Everything I've said so far comes to bear on what you are likely to obtain when you buy an older boat. One of the things that we pay close attention to in performing a survey on a used boat is how much jury-rigging and alterations there are in the electrical system. Sometimes there's a lot, and if the new owner isn't willing to foot the bill to make corrections, more often than not he's going to be living with a lot of electrical headaches. In most cases, he's not even aware of why things are constantly breaking down; he just knows that things unexpectedly keep crapping out. Usually he blames the pump or motor, or whatever gizmo that fails, when actually faulty wiring is the problem. Beware that on boats with bastardized electrical systems, the cost of straightening it out and cleaning it up can be pretty high.
Adding New Equipment
Most boats, particularly smaller ones, are unfortunately not designed with the idea of adding equipment, even though nearly everyone does. But the primary reason why systems gets so messed up results from the attempt to force something in where there is no provision for it.
The best way to deal with this is to simply add a new panel, whether AC or DC. Doing this is neither very difficult nor expensive, especially considering the cost to repair all the problems you're likely to create when you try to cram something onto a system not designed to handle it. A six breaker DC panel will cost less than $200 and is a whole lot better than scattering inline fuses all over the place, and with installation will run less than $500. Plus, the new panel can be added at any location where it will be convenient.
Adding a second shore power circuit is especially useful for those boats with single 30 amp shorelines where the addition of new equipment will tax the system. It's not very convenient to have to turn the water heater off to turn the air conditioning on, or constantly be managing equipment as breakers keep popping off. You have two options here, the first of which is to increase your shoreline to 50 amps. To do that you have to change the main breaker, power receptacle and the shore cord, which is a lot bigger and heavier. The other option is to add a second 30 amp circuit, which means adding a new panel, receptacle and shore cord, which costs a bit more.
Adding a second circuit has the advantage of separating the air conditioning onto a separate line, which is the way all good systems are designed. That's because of the high power demand, combined with frequent dock power faults, makes it desirable to separate it from the main service.
A multiplex system is a multiple power source system which permits switching from one line to another, from one power source to another. For travelers, this is extremely useful to deal with unreliable dock power, or sudden faults in your own system. It allows you to choose which line you want to run equipment on, and particularly if you have a generator, it provides a great deal of flexibility. Let's say a circuit breaker on the dock goes out while you're cooking dinner and it's very hot this day. Instead of only being able to turn the AC off and go on cooking in the heat, you can fire up the generator to run the failed circuit simply by switching it over. The better larger boats invariably have this kind of system.
The reason why low cost boats don't have this kind of system is because it requires the use of very expensive rotary switches that costs $300 - $600, plus some more complex wiring. But it is an extremely good system to have. See photo below.
As versatile as it can get. This boat has (2) 125 and (1) 250 shorelines plus generator for a total of 4 power sources. These are controlled by the six rotary switches, each with four positions, so that any combination of power sources on any branch circuit can be selected.
Posted November 12, 1998 (First posted July 14, 1998 at www.yachtsurvey.com. Revised and added two pictures November 02, 1998. Page design changed for this site.)