Something about 12-volt DC power seduces and encourages hack electricians to try their hand using household-grade wire and terminals. In my several decades of owning and working on boats, I have personally seen more examples of scary do-it-yourself DC electrical projects than any other type of boat equipment disaster. Don’t take shortcuts when wiring your boat, or you may compromise the safety of your boat and crew. This is critically important because, according to BoatUS Marine Insurance, problems with DC electrical systems are responsible for 32 percent of onboard fires, more than any other category of causes. Safety onboard begins with a reliable DC electrical system, properly installed with quality wiring, connections and components. Put it in a corrosive environment, where wiring and electrical components are subjected to more concentrated daily abuse than your family car will experience in five years, and it’s easy to see how small electrical problems can get out of hand very quickly. That same truism can be applied to your boat’s DC electrical system. Does your boat have a similar legacy of bad electrical work? The amazing thing is that all of the systems still worked. This table is for 12-Volt systems only.Behind these gold-colored switch panels lurked a 40-year-old tangle of do-it-yourself wiring projects. Remember that the Length is a round-trip distance. Use 10% voltage drop for non-critical applications such as windlass, cabin lights, circuits other than running lights, electronics or panel board feeds. Use 3% voltage drop for critical applications affecting the safety of your boat and crew, such as running lights, blowers, electronics and panel board feeds. If 7–24 conductors are bundled, reduce amperage by 50 percent. If 4–6 conductors are bundled, reduce maximum amperage by 40 percent. Conductors are not bundled: If three conductors are bundled, reduce maximum amperage by 30 percent.Wires are not run in engine spaces: Maximum current is 15 percent less in engine spaces, which are assumed to be 20☌ hotter than non-engine spaces (50☌ vs.SAE wire sizes are 6 to 12 percent smaller, carry proportionally less current, and have greater resistance AWG wire sizes, not SAE: All Ancor wire uses AWG wire sizes.

Lower temperature insulation cannot handle as much current 105☌ insulation rating: All Ancor wire uses 105☌ insulation rating.This simple equation allows you to calculate the voltage drop for a circuit of any length and any current flow, if you know the resistance of the wire.įinally, note that the amp capacity (ampacity) of the wire curtails using very short lengths of wire for large current flows, as shown by the “flat tops” of the 10% chart areas. Voltage Drop = Current x Length x Ohms per foot We’ve included copper wire specifications which comply with the AWG standards at the bottom.

The wire size listed in the graph at the intersection denotes the gauge of wire to use.

Find the length of the circuit on the vertical axis of the chart, noting that the length is the round-trip distance from the panel or battery to the load and back.

Find the current consumption of the load on the horizontal axis of the chart.

Select either the 10% or 3% voltage drop chart, based on the type of load you are running.

The simplest method we’ve found uses the charts below. Use the charts below to determine the correct wire gauge, based on the amount of current in the circuit and the length of the wire run.Įven the experts have to check occasionally on the correct gauge and ampacity (maximum amount of electrical current a conductor can carry) of wire for a given marine DC load. Marine grade wire is manufactured in multiple gauges for different applications.

Marine wire gauge chart