Download Voltage Drop Reference - Western Marine Company

Voltage Drop Reference
Voltage Drop / Cable Size / Length Chart
ABYC specs ask for 3% maximum voltage drop [VD] for navigation lights, switch board feeders, bilge blowers
and electronic equipment. Other circuits ie motors and general lighting can have a maximum 10% VD.
The chart shows conductors in an ambient
temperature of 30oC. Engine room temperatures
are assumed at 50oC. This requires a rating
decrease of 15% ampacity.
Example 1: A 10-AWG cable in a 12V circuit has a
total Cable run of 40’ from the battery to the load
and back. Table A Shows that the maximum
amperage this cable can carry without exceeding
a 3% voltage drop is 5amps. If a 10% Voltage drop is
acceptable, Table B shows that this rises to 25amps.
Because of the relatively long cable run, the voltage
drop is the limiting factor in cable sizing.
Example 2: A 12-V bilge pump draws 8amps and is situated 30’ from its battery, so the total cable run is 60’.
To select a cable that will keep the voltage drop below 3%, a builder would use the 12-V columns in Table A,
and look down the left hand column to 10amps [the closest reading above 8amps] The numbers to the right
are AWG sizes based on total cable runs. For 60’ 6 AWG is listed In this case.
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