Nothing in boating is as scary or as dangerous as a fire or explosion on board. Nothing starts a fire faster than an electrical spark from an improper or corroded electrical connection. The American Boat and Yacht Council (ABYC) establishes rigorous standards for manufacture and repair of electrical equipment, wiring, connectors and circuitry. Boat manufacturers use these standards as an absolute rulebook in designing and building ever safer boats. Unfortunately, these same electrical standards are among the most ignored, misunderstood and abused by boat owners.
A new GPS; a failed bilge pump; or a replacement VHF radio; many of us consider that we can repair or install basic electrical wiring. However, many of us simply don't know the rules governing boat wiring. Others use the same techniques and tools that we use around our homes, and most of us buy our tools and supplies at the local hardware or home supply store. All of these can lead to disaster on our boats. The ABYC standards should be a rulebook for boat owners just as it is for the manufacturers. This article highlights some of the basic electrical standards that should guide our do-it-yourself marine electrical projects.
Choose the right wire: A common misconception is that its only 12 volts - what harm can that do? What we fail to realize is that 12 volts is more than enough to start a fire with a spark, splatter molten metal, and cause serious injury (remember to remove jewelry and watches when working around electricity).The measure of power required by electrical equipment is measured in watts. Watts is current (measured in amps) times volts. With only 12 volts available, marine equipment must draw much more current to get enough power to operate than a simple 120 volt household appliance. The amount of current (amps) determines the size of wire required. A common marine head pump draws over 25 amps and stereo amplifiers often require 40 amps or more. The more current flowing through a wire, the more heat it generates, and the bigger the spark when a connection fails. Wire that stereo amp with too small of a wire and you are asking for a fire.
Marine wiring is unique, requiring both flexibility and resistance to corrosion. Unlike residential wiring that is protected by the wallboard, rarely disturbed or subject to vibration, wiring and connectors on boats are constantly being vibrated, bounced, and subjected to temperature variations, humidity, water, and corrosives. Where solid wire and wire nuts are common in residential wiring, both are explicitly banned by ABYC marine standards.
In order to be flexible and corrosion resistant, marine wiring must be stranded copper - multiple copper wires within a common insulating jacket. While not required, most marine wiring is tinned to reduce or slow corrosion. For 12 volt DC wiring, estimate the total distance from the source of power (e.g. the DC breaker panel) to the device and back - the round trip distance. Using that distance and the current required (Amps = Watts divided by 12 volts), ABYC tables specify the minimum size wire required. Wire size is measured in gauge (AWG = American Wire Gauge), with smaller numbers indicating larger diameter wire. The smallest gauge wire approved by ABYC for any DC wiring is AWG 16. High current devices like stereo amplifiers often require very heavy AWG 6 or AWG 4 wire, especially if they are located some distance from the battery or DC breaker panel.
Note that stranded marine-grade wire is also required for AC (120 volt) circuits on boats - the wire (commonly called Romex) that we use in our homes is not certified for use in boats, because the conductors are solid. Instead, AC circuits on boats must use 600 volt 3 conductor, stranded and sheathed marine grade cable, often called "Boat Cable."
When running either DC or AC wiring, leave enough slack that the wire can move as it needs to compensate for temperature and flexing of the boat, but snug enough that the wire doesn't bounce around in rough seas. Be especially careful about wires being too loose or too tight going around corners and through bulkheads. All wiring must be secured to minimize movement and to prevent it from falling against anything that could damage the insulation. Plastic cable ties ("zip ties") are the most common method and should be spaced at most 18 inches apart. Use wire ties with an included screw connection to secure wiring against bulkheads. Pull the cable tie snugly, but not so tight that the wire cannot move through it lengthwise. Pay particular attention to places where the wire may rub against other equipment or boat structures. Split flex tubing is especially useful in protecting wiring, but be sure to secure the ends and middle of the flex tubing with wire ties to keep it in place.
Make the right connection: Connections at the ends of wires and splices in the middles are the most frequent points of failure for any wiring, especially in boats. Corrosion, stress, vibrations, and movement are the enemies here as well. ABYC standards are explicit in how connections must be made, recognizing that stranded wire requires special techniques and tools.
Wire nuts (cone shaped devices with a spiral wire or plastic threads inside) that most of us are familiar with in our home lighting are specifically banned by the ABYC. Wire nuts are not designed to be used on stranded wire. Even in residential use, one of the wires must be a solid (non-stranded) wire. To tighten correctly, the wire nut will cut fine grooves or threads into the solid wire. When both wires are stranded as on a boat, the wire nut won't tighten adequately and worse yet, may actually cut or break the fine wires in the strands. Because they can't cut threads into the wire, wire nuts are subject to loosening with vibration. Finally, they are difficult to seal against water and corrosives. It makes sense that they are banned by ABYC.
The preferred method of splicing wires or connecting wires to circuit breakers or equipment is using crimp connectors. The boating, home supply, and discount stores sell inexpensive kits of typical size connectors and an inexpensive combination stripping and crimping tool. The typically contain a few dozen spade, ring, and male/female blade connectors and tubular butt splices, each with brightly colored vinyl jackets. These connectors have two basic flaws. First, the vinyl jackets are easily dislodged and/or pierced when installing them, and second, the barrels (the tubular part of the connector that holds the wire) have a split in them that when crimped can cut or otherwise damage the wires inside. The crimpers sold in these kits either have two concave sides or a single concave side to hold the connector while a "bump" presses into the connector from the other side. These crimpers are notorious for not crimping firmly enough or piercing the vinyl jackets. The ABYC standard doesn't ban the use of vinyl-jacketed connectors, or inexpensive-style crimpers, but the standards do specify that once crimped the connector must withstand a certain force attempting to pull the connector off the wire. These force standards are extremely strict. For example, an AWG 14 wire and connector that might be used to power a bilge pump must be able to withstand 30 pounds of force attempting to pull the connector off. Imagine hanging a 30-pound bag of potatoes or dog food from the ring connector on the end of a 14-gauge wire! It is virtually impossible to adequately crimp a connector using an inexpensive or piercing crimper to meet that standard, and if we do, chances are that the split barrel will have cut some of the wire strands, and that the insulation jacket was pierced exposing the wire to corrosion.
While more expensive, marine connectors should be nylon jacketed and attached using a ratcheting crimper. The nylon jackets are much more rugged and puncture resistant. They are easy to recognize by their semi-transparent jackets, and come in the same sizes and styles as the others. Ratcheting crimpers are sold by better marine suppliers and cost $75-$100. An example is shown in the title figure.
For most applications where the wire is to be screwed down, ring connectors are preferred. Note that curling the wire into a hook as is done in residential switches and outlets is not acceptable for marine use. In some equipment where a compression plate is between the screw head and the wire, a ring connector is not required, but it is still a good idea. Basically forked connectors, especially the flat forked connectors sold in the inexpensive kits are not recommended because they can easily be pulled out if the screw is not tight. The flat forked connectors are banned by ABYC, while the forked connectors with small hooks on the end of the forks are acceptable in cases where it is hard to remove and replace the screw.
Butt connectors are the preferred way of splicing two wires. Essentially a tube, the two wires are inserted in the two ends of the tube and each is crimped. Step-down butt splices are available when the two wire sizes are radically different; however, in most cases, the same size wire should be used throughout a project.
For applications in bilge and engine spaces, or where the wire may be exposed to water, the above nylon jacketed connectors and butt splices are available with hot-melt adhesive inside. Insert the wire and crimp it as before, but when complete, heat the connector with a heat gun to melt the adhesive and seal the connector. For obvious reasons, lighters and matches should not be used and can burn the insulation. Conventional shrink-wrap tubing is invaluable for sealing and protecting electrical splices and connections. For real waterproofing, use the kind with heat sensitive adhesive on the inside.
Another common misconception dictates that the best of all connections is a soldered connection. However with stranded wire, the solder bonds the individual strands together, making a solid, inflexible wire. ABYC standards prohibit soldering as the sole means of making a connection because the newly solid wire is subject to cracking or breaking through vibration and flexing. A more practical solution is to use a crimp connector described above. Wires should never be joined simply by soldering and taping (or heat shrink); however, if solder is used, use only 60%/40% rosin core or solid solder, soldering after the butt connector is crimped. Acid core solder as used in plumbing may never be used in any electrical wiring.
One final word about electricians tape: we all have a roll of black electrical tape in our toolboxes and we all use to fix a myriad of problems, including wrapping electrical connections. As a quick, temporary way to insulate a wire or connection, it is unsurpassed, but it should be just that - temporary. Electrical tape is not impervious to water, often loses its stickiness when wet, shrinks and comes loose over time, and leaves a black sticky mess in its wake. Use it if you must, but be sure to replace it with shrink tubing or a more permanent solution as soon as practical.
This article is but a very brief introduction to marine electrical wiring. The emphasis is only to introduce a series the wiring standards and practices dictated by the ABYC, and to erase a few misconceptions. The USPS Electromechanical Systems Committee (EMSCom) has just released an outstanding new USPS Marine Electrical Systems course. MES is a much more thorough presentation of marine wiring, standards, techniques, reading and interpreting schematics, grounding and understanding how DC and AC systems operate. The course emphasizes the ABYC standards and how to use them to make your boat safer and more reliable. We strongly encourage everyone to take MES at the earliest opportunity.
The American Boat and Yacht Council, Inc. (ABYC) is a non-profit, public service membership organization with over 4000 individual and corporate members worldwide. ABYC produces, publishes, and distributes safety standards and technical information reports for the marine industry. In addition to writing standards, ABYC has a comprehensive education and workforce certification program that began in 1989. ABYC and USPS have a Joint Memorandum of Understanding.
D/Lt/C Jeff Wise, SN is a past commander of the Atlanta Sail and Power Squadron, and a member of the USPS Electro-magnetic Systems Committee. He is a member of ABYC and a leading partner in Apogee Marine, Inc., a firm specializing in installation and repair of recreational and commercial marine electrical and electronic systems.