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Amps and Wire Gauge in 12V Electrical Circuits

Maximum current - amps - through a 12V circuit - related to size (AWG) and length of wire

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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)

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Maximum Current (amps)
5101520253040506070
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

  1. calculate total length of wire from source to device and back again
  2. determine amount of current in wire
  3. 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 mm2cable with length 15 m is approximately 5 amps.

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