Wire Sizing Chart
1.Calculate the maximum sustained amperage of the circuit. Measure the length of the circuit from the power source to the load and back.
2.Calculate Famps (Feet x amps). Multiplycircuit lenght by max. current.
3.Base the wire on either the 3% or 10% voltage drop. In general, items which affect the safe operation of the boat and its passengers (running lights, bilge blowers, electronics) use 3%; all other loads use 10%.
4.Are the circuit runs in an engine space or non engine space?
5.Starting in the Famps column with the right voltage and voltage drop, run down the list until arriving at a value which is greater than the calculated Famps. Move left to the Ampacity column to verify that the total amperage of the circuit does not exceed the maximum allowable amperage of the wire size for that row. If it does, move down until the wire ampacity exceeds the circuit amperage. Finally, move left to the wire size column to select the wire size.
Example
A 12 volt system at 10% drop with a 40’ circuit x 45 amps = 1800 Famps. A wire size of 8 is required.
Note: For wire with 105°C insulation rating and AWG wire sizes.
Chart courtesy of the West Advisor
| TO DC HOUSE |
| DISTRIBUTION |
TO 24 HOUR | PANEL OR HIGH |
CIRCUITS | AMP DC LOAD |
LED | LED |
100A
LED LED
|
| 1 |
OUTPUT TO | COMMON | 2 |
ENGINE | ||
ALTERNATOR |
|
|
OR STARTER |
|
|
BATTERYLINKTMACR
BA
HOUSE |
ENGINE |
DC NEGATIVE
DISTRIBUTION BUS
Wiring Diagram
Dual Battery Main Distribution Panel
