12 Gauge Wire (12/2 Wire, 12/3 Wire, 12/4 Wire) Ampacity: How Many Amps Can 12 Gauge Wire Safely Handle?
12 gauge or 12 AWG 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 10-15 Amps current.
However, current carrying ability differs depending on the maximum allowed wire temperature, wire length, and similar.
Updated: May 16, 2023.
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" - 12 gauge wire Amp rating) depends on the maximum allowed wire surface temperature, and for enclosed 12 gauge solid copper wire, these values are:
- @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.
Also, wires placed in conduit feature so-called "Conduit Ampacity Derating": the process of reducing the current-carrying capacity (ampacity) of a wire or cable based on certain factors, primarily the number of current-carrying conductors in a conduit and the ambient temperature.
When more conductors are present in a conduit, or the temperature is high, the heat dissipation is less efficient, which can cause overheating.
Therefore, to ensure safe operation, the rated ampacity of the conductors must be derated (reduced) according to guidelines provided in electrical codes, like the NEC in the United States.
12 Gauge/12 AWG Wire Ampacity In Free Air
12 gauge/12 AWG wire Amp ratings are not the same for the enclosed wires and for wires free in the air. Also, it depends on the wire material, i.e., copper or aluminum.
The following chart lists default Ampacities for 12 gauge solid copper and aluminum wires in free air:
|Temperature||12 Gauge Copper Wire||12 Gauge Aluminum Wire|
|60°C / 140°F||30||25|
|75°C / 167°F||35||30|
|90°C / 194°F||40||35|
Due to better cooling and other reasons, wire Ampacities in the air have larger values than those for enclosed wires.
Note: these are "default" Ampcities, and when calculating real values, don't forget "80% Rule" and "10% Rule". Also, always check local laws, regulations, and standards.
So, if You want to know how many Amps can 12 gauge wire handle, it depends on the wire material (copper or aluminum), wire length, if the wire is free in the air or enclosed, how many wires are enclosed in what conduit, etc. Generally, short 12 gauge wires can handle 15-16 Amps if not enclosed with more than 3 wires - again, this depends on the exact application of the wire.
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 if they should 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 (What about Conduit Ampacity Derating? So, even those 16 Amps are questionable...) 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 the documentation!
12 gauge wires are very often used as lighting wires, and as such, they are often labeled as 12/2 wires or 12 2 wires.
12 Gauge Wire Cables: 12/2 Wire, 12/3 Wire, and 12/4 Wire
Wires are rarely used individually - they are most often arranged in cables consisting of several wires.
Hence, cables can be labeled as 12/2 Wire (also written as "12 2 Wire"), 12/3 Wire ("12 3 Wire"), and 12/4 Wire ("12 4 Wire") - cables with more wires than 4 wires are generally rare and are often custom-built.
When the cable is labeled as, for example, "12/3 Wire", that means that it is a cable consisting of three 12 gauge wire conductors and one ground wire. Thus:
- 12/2 Wire (12 2 Wire) consists of two 12 gauge wire conductors and one ground wire.
- 12/3 Wire (12 3 Wire) consists of three 12 gauge wire conductors and one ground wire.
- 12/4 Wire (12 4 Wire) consists of four 12 gauge wire conductors and one ground wire.
In order to help the user properly connect the wires, they are color-coded.
Actual color codes depend on the intended wire/cable use - color codes differ for DC (Direct Current), for 120/208/240V AC, for 277/480V AC wiring, and from country to country.
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 ...