Tips on
Electrical System Use and Maintenance

Part III: DC Systems

by David H. Pascoe, Marine surveyor 

DC Systems

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.

Circuit Protection 
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
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.

Proper Lugs 
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.

Ventilation
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 Weather
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.

Engine Wiring
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.

Posted November 15, 1998 (First posted July 14, 1998 at www.yachtsurvey.com. Revised and added two pictures November 02, 1998.  Page design changed for this site.)