12 Gauge Wire Ampacity: How Many Amps Can 12 Gauge Wire Safely Handle?
12 gauge wire is a very popular wire thickness used for speakers, extension cords, home, and car electric installations, and for all other applications where a wire must safely handle 10-20 Amps current.
However, current carrying ability differs depending on the maximum allowed wire temperature, wire length, and similar.
Published: June 14, 2022.
12 Gauge Wire Dimensions/Thickness
12 gauge wire or AWG 12 wire features physical dimensions of:
- diameter: 2.0525 mm, 0.0808 inches
- cross-section area: 3.3088 mm2, 0.0051 inches2.
Note: these values are for solid copper 12 gauge wires - copper 12 gauge stranded wires feature somewhat different but very similar values.
12 Gauge Wire Amps
Default 12 gauge wire ability to carry current (also known as wire "Ampacity") depends on the maximum allowed wire surface temperature:
- @60°C/140°F: 20 Amps max. continuously,
- @75°C/167°F: 25 Amps max. continuously,
- @90°C/194°F: 30 Amps max. continuously.
For safety reasons in most applications, one uses Ampacity provided for 60°C/140°F temperature (20 Amps max.), but other surface temperatures may be acceptable, depending on the situation.
However, before fully accepting these Ampacity values, there are a few additional rules to consider first.
The 80% Rule is a very important safety rule which basically means that the wire's actual Ampacity is 80% (hence the name of the rule) of the wire's default/theoretical Ampacity. For 12 gauge wire, that means:
- @60°C/140°F: 20 Amps * 0.8 = 16 Amps
- @75°C/167°F: 25 Amps * 0.8 = 20 Amps
- @90°C/194°F: 30 Amps * 0.8 = 24 Amps
That means that for most applications that allow a maximum wire surface temperature of 60°C/140°F, the actual Ampacity is 16 Amps and not 20 Amps!
However, what about wire length?
Wire Length - 10% Rule
When the wire is longer, in order to decrease the energy losses, the 10% Rule is applied - for every 50 feet (~15m) of wire, Ampacity is decreased by 10%.
In real life, that means that the 12 gauge 150 feet long wire @60°C/140°F, the Ampacity is:
I (A) = 20 * 0.8 / 1.3 = ~12.3 Amps
The following chart lists the Ampacity of 12 gauge wire at certain temperatures for the wires of 0 (80% Rule), 50, 100, 150, and 200 feet.
|Wire Length / Temperature||@60°C/140°F||@75°C/167°F||@90°C/194°F|
Note: Rules, regulations, and laws may differ from country to country, so if unsure, consult a certified local electrician or a local company.
10 Gauge Wire vs 12 Gauge Wire vs 14 Gauge Wire
10 gauge, 12 gauge, and 14 gauge wires are relatively similar wires, differing in their thickness and Ampacity. The following comparison chart lists 10, 12, and 14 gauge wires thicknesses and the default Ampacities (given in Amps) at three different temperatures:
As one can see, 12 gauge wire is thicker than 14 gauge wire and 10 gauge wire is double the thickness of 14 gauge wire (cross-section area). Similarly, 10 gauge wire can handle more current than 12 gauge wire which can handle more current than 14 gauge wire.
12 or 14 Gauge Wire For Outlets?
Many people wonder should they put 12 gauge wire or 14 gauge wire for outlets (from the circuit breaker to the wall power outlet).
Personally, one should put at least 10 gauge wire from the circuit breaker to the wall power outlet - very short 12 gauge wires can handle 16 Amps continuously with the maximum wire surface temperature of 60°C/140°F, but why risk overheating the wires.
Anyway, when placing wires at home, boat, or similar, check the documentation of the electric system and do as recommended by a certified electrician.
Note: while electric cables can be over-dimensioned, electric breakers MUST be dimensioned as specified in documentation!
Long Story Short: Electric wires are intended to last for many years to come - and they do, when dimensioned properly. When too thin wires are used, they often overheat, leading to damaged insulation, short circuit, and electric breakers popping out, with an increased risk of smoke and fire.
Using too thin wires can lead to small money saving in the short run, but in the long run potential problems are much more expensive... not to mention dangerous ...