Amps and Wire Gauge in a 12V Electrical Circuit
Maximum current - amps - through a 12V circuit - related to size (AWG) and length of wire
Conductors in electrical systems should not be sized with voltage drops exceeding 3%.
For a 12V system the maximum voltage drop should be less than (12 V) x 3% = 0.36 V.
Conductor sizes (AWG) related to maximum current through a 12V electrical wire and length of cable - are indicated below:
| American Wire Gauge (#AWG) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Length (feet) | Maximum Current (amps) | |||||||||
| 5 | 10 | 15 | 20 | 25 | 30 | 40 | 50 | 60 | 70 | |
| 15 | 16 | 12 | 10 | 10 | 8 | 8 | 6 | 6 | 4 | 4 |
| 20 | 14 | 12 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 4 |
| 25 | 14 | 10 | 8 | 8 | 6 | 6 | 4 | 4 | 2 | 2 |
| 30 | 12 | 10 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 2 |
| 40 | 12 | 8 | 6 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 |
| 50 | 10 | 8 | 6 | 4 | 4 | 2 | 2 | 1 | 1/0 | 1/0 |
| 60 | 10 | 6 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 2/0 |
| 70 | 10 | 6 | 4 | 2 | 2 | 2 | 1/0 | 2/0 | 2/0 | 3/0 |
| 80 | 8 | 6 | 4 | 2 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 |
| 90 | 8 | 4 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 3/0 | 4/0 |
Note! Failure to use an adequate size may result in a fire. Always secure electric wires with fuses.
- 1 ft (foot) = 0.3048 m
Wire Gauge Design Procedure
- calculate total length of wire from source to device and back again
- determine amount of current in wire
- determine correct wire gauge in the intersection of amps and feet
Note! Wire size based on 3% (0.36 V) voltage drop in a 12 Volt circuit. Always oversize wires if voltage drop is critical.
print 12V Cable Length Diagram
Example - 12 V Cable and Maximum Length and Current
The maximum current in a 12 V gauge #6 (13.3 mm2) cable with length 15 m is approximately 15 amps according the diagram above.
The maximum current in a gauge #10 (5.26 mm2) cable with length 15 m is approximately 5 amps.
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