Automotive & Marine Wire Sizing Chart
BRANCH CONDUCTOR | Conductor Length |
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Table cell colors are for visual purposes only and do not indicate physical wire color or temperature.
While this wire gauge table outlines specifics for single copper conductors in Free Air per the NEC, your automotive electrical installation does not necessarily conform to a “Free Air” definition. Granted, your conductors are not installed in a heat encompassing shield such as metal conduit or PVC tube either. Your conductors may be held firmly inside (breathable) wire loom or sleeving, and may be tie-wrapped or secured with a multitude of other conductors.
However, we can appropriately suggest that you increase the Ambient Temperature correction factor to allow for any (or all of the above) heat restraints.
| 3’ | 5’ | 7’ | 10’ | 15’ | 20’ | 25’ |
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Total Load Amps (A) | Gauge sizes are based on single copper conductor in free air per NEC standards |
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3 | 18 | 18 | 18 | 18 | 18 | 18 | 16 |
5 | 18 | 18 | 18 | 18 | 16 | 16 | 14 |
7 | 18 | 18 | 18 | 16 | 14 | 14 | 12 |
9 | 18 | 18 | 18 | 16 | 14 | 12 | 12 |
10 | 18 | 18 | 16 | 16 | 14 | 12 | 12 |
12 | 18 | 18 | 16 | 14 | 12 | 12 | 10 |
15 | 18 | 16 | 14 | 14 | 12 | 10 | 10 |
18 | 18 | 16 | 14 | 12 | 10 | 10 | 8 |
20 | 18 | 16 | 14 | 12 | 10 | 10 | 8 |
22 | 16 | 14 | 14 | 12 | 10 | 8 | 8 |
24 | 16 | 14 | 12 | 12 | 10 | 8 | 8 |
30 | 16 | 14 | 12 | 10 | 8 | 8 | 6 |
40 | 14 | 12 | 10 | 10 | 8 | 6 | 6 |
50 | 14 | 12 | 10 | 8 | 6 | 6 | 4 |
60 | 12 | 10 | 8 | 8 | 6 | 4 | 4 |
70 | 12 | 10 | 8 | 6 | 4 | 4 | 2 |
80 | 12 | 10 | 8 | 6 | 4 | 4 | 2 |
90 | 10 | 8 | 8 | 6 | 4 | 2 | 2 |
100 | 10 | 8 | 6 | 6 | 4 | 2 | 2 |
125 | 10 | 8 | 6 | 4 | 2 | 2 | N/A |
150 | 8 | 6 | 4 | 4 | 2 | N/A | N/A |
Conductor Voltage Drop
13.8V nominal voltage
Maximum Voltage Drop
NEC standards allow for a maximum 3% voltage drop in feeder conductors, and a maximum 5% voltage drop in branch conductors. Some loads may require even more stringent % values. If in doubt, consult the manufacturer of your specific load.
Branch Conductor
Branch conductors are sized to carry 100% of load rated amperage per the NEC
minimal requirement for non-continuous use (defined by the NEC as having less than 3 hours of continuous use).
Feeder Conductor
All feeder conductors are sized slightly larger than the NEC minimal requirement for non-continuous use.
Feeder conductors are sized to carry a minimum of
125% of the largest single load amperage plus the total amperage of all
other individual loads that are connected with the feeder conductor.
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