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Marine Wire Size and Ampacity


Even 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. The simplest method we’ve found uses the charts below.

  • Select either the 10% or 3% voltage drop chart, based on the type of load you are running.
  • Next, find the current consumption of the load on the vertical axis of the chart.
  • Find the length of the circuit on the horizontal axis of the chart, noting that the length is the “round trip” distance from the panel or battery to the load and back.
  • The color of the graph at the intersection denotes the gauge of wire to use.

We’ve included copper wire specifications which comply with the AWG standards at the bottom.

Of particular interest is the equation:
Voltage Drop = Current x Length x Ohms per foot

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.

Finally, note that the amp capacity of the wire curtails using very short lengths of wire for large current flows, as show by the “flat tops” of the 10% chart areas.

Marine Wire Marine Wire

Wire Gauge Color Code

Colors in above charts correspond to AWG wire sizes below:

Marine Wire

These simple, proprietary graphs assume:

  1. 105°C insulation rating: All Ancor wire uses 105°C insulation rating. Lower temperature insulation cannot handle as much current (the flat tops on the 10% graph would be lower than shown)
  2. AWG wire sizes, not SAE: All Ancor wire uses AWG wire sizes. SAE wire sizes are 6%-12% smaller, carry proportionally less current, and have greater resistance
  3. Wires are not run in engine spaces: Maximum current is 15% less in engine spaces, which are assumed to be 20°C hotter than non-engine spaces (50°C vs. 30°C).
  4. Conductors are not bundled: If three conductors are bundled, reduce maximum amperage by 30%. If 4–6 conductors are bundled, reduce maximum amperage by 40%. If 7–24 conductors are bundled, reduce amperage by 50%.

To Complete Your Project, Don’t Forget:

  • Heat Shrink Tubing
  • Wire Strippers, cutters and crimpers
  • Terminals: ring, spade or butt connectors

AWG Wire Specs

Wire Size (AWG) Nominal OD Weight per 1000' Cir.Mil. Area Square mm Ohms per 1000' Max Amps
18 7/64" 12lb. 1,600 0.823 6.48 20
16 1/8" 16lb. 2,600 1.31 4.00 25
14 9/64" 23lb. 4,100 2.08 2.50 35
12 5/32" 31lb. 6,500 3.31 1.75 45
10 7/32" 44lb. 10,500 5.26 0.98 60
8 5/16" 86lb. 16,800 8.37 0.62 80
6 11/32" 18lb. 26,600 13.30 0.40 120
4 13/32" 178lb. 42,000 21.15 0.24 160
2 15/32" 277lb. 66,500 33.62 0.157 210
1 17/32" 350lb. 83,690 44.21 0.127 245
1/0 9/16" 437lb. 105,600 53.49 0.099 285
2/0 5/8" 549lb. 133,000 67.43 0.077 330
3/0 11/16" 675lb. 167,800 85.01 0.062 385
4/0 13/16" 837lb. 211,600 107.20 0.049 445