Electrical systems and parts on a boat are in a very corrosive environment, one not made for anything electric. This makes it more critical to be safe and sure about stopping an electrical problem before it even happens. Marine electrical systems basics are important because wiring and electrical components in a marine environment go through more abuse and wear – maybe even in a day – than a car’s electronics might go through in years of use.
“The strongest chain is only as reliable as its weakest link.”
That very same saying goes for a watercraft’s DC electrical system. It’s simple to see how any electrical issue can escalate extremely quickly. Safety onboard starts with a good, sound DC electrical system, appropriately installed with safe wiring, connections and parts. Do not take shortcuts with electrical wiring on a boat, or you might compromise the security of your family and friends. According to BoatUS Marine Insurance, 32 percent of marine craft fires start from problems with electricity or electronics. This category is the highest percentage.
If you’re not knowledgeable about basic electrical practices and theory, hire a person who is, and let them do any electrical work or mount those cool devices like a fishfinder, LED cabin lights or subwoofers.
What Wires Can Be Used on a Boat?
Some types of “regular wire” is able to be used on boats or marine craft in some uses. If the wire is SAE J378, J1127 or J1128. These wires are developed for “surface vehicles,” and fine for minimum standards for some uses on a boat. These types do not meet marine industry requirements and special requirements for some specific uses.
Even if tinned copper, your wiring must not be run in bilge rooms or certain locations subject to moisture from spray or leaking. The American Boat and Yacht Council (ABYC) criteria include this rule: “Current-carrying conductors shall be routed as high as practicable above the bilge water level and other areas where water may accumulate. If conductors must be routed in the bilge or other areas where water may accumulate, the connections shall be watertight.”
Wires should not be run in engine spaces, unless marked “oil resistant” and “75C”. They ought to not be used where vibrations or frequent flexing will occur. They shouldn’t be used where 110 volt applications are needed. For safety, use the appropriate wire marked with the correct size and type.
Most significantly, SAE wire is up to 12 percent smaller than American Wire Scale (AWG) Boat Cable. This means in many uses larger gauge wiring needs to be used so the potential voltage drop limit recommended is safe. The cord charts located in Chapman’s Aviation as well as other publications are all for AWG cord like that made by our provider, Ancor, not SAE kind cable. In general, electrical wiring on watercrafts must be of the stranded type, not solid copper wire used in home applications, which does not withstand the vibrations often created on a watercraft.
With that said, it’s typically better and smarter to use real marine grade wiring.
Factors to Know about Marine Electrical Systems Basics
Using larger wiring might be expensive and it adds bulk and weight to a boat. Using wiring that’s too small or too light may be inadequate for the power you need or wind up being a safety hazard.
Ampacity
Ampacity is the current carrying capacity of a device or component which is a conductor. Amps is the measure. Many electrical devices, for instance LED lights, use a consistent capacity of amps and this makes it easy to know the amps needed for a device.
On the other hand, devices such as power inverters or motors may cause a surge or spike, especially when it’s starting. A circuit needs to safely handle the maximum possible amps of all the devices on it.
If you’re setting up an anchor windlass that usually draws 80 amps, but may draw a maximum of 300 amps when attempting to break an anchor loose from a rough bottom, you need to size the electrical wiring appropriately.
Temperature
The temperature where you are running your electrical wiring influences how much electric current it can handle. The warmer the ambient temperature of the environment, the lower the amps wiring can carry.
So, if you’re running wiring through a boat’s engine room, ABYC requirements assume the temperature level is 122°F (50°C). If you’re running a circuit with #6 AWG cable size, it can securely carry 80 amps outside in more typical temperatures, but it’s only 46.4 amps at 122 degrees in the hotter engine room. As a rule, a maximum current is 15 percent less in engine rooms, which are figured to be 20°C hotter than non-engine spaces.
Cable Bundling
While on the subject of heat, when wires are bundled together, it creates more heat. A bundle of wires, cords and cables doesn’t let heat dissipate as well as normal. This is something to be familiar with, yet the ABYC regulations applies only to circuitry of 50 volts or more, so it is typically a problem with AC circuits on a watercraft, not a usual 12 volt DC wiring installation.
As a general estimate, if three conducting wires are bundled, it reduces the maximum amps by 30 percent. If it’s a bundle of 4-6 wires, it’s an estimated 40 percent reduction; and 7-24 wires causes a loss of about 50 percent.
Voltage Drop
Voltage drop, another important factor in wire sizing, is about the effect length of wiring has on resistance and voltage. Each wire has a degree of resistance, so in a DC circuit, you will predictably lose some of the amount of energy that’s turned into heat. The longer the wiring has to be run, the more the voltage declines. This can be a real trouble with some types of electronic devices or with electric motors, which will run slower at 11.5 volts.
The answer is to use wires with reduced interior resistance – a larger diameter wire, considering that bigger wires have less resistance.
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