How Many Amps Will 12/2 Wire Carry?

12/2 wire amp rating

12/2 wires have a thickness of 2.053mm (0.0808 inches), a cross-section of 3.31 mm2, 12.4 turns per inch (4.87 turns per cm), and a resistance of 5.211 milliohms per meter. ‘12/2’ is 12-gauge wiring. That second figure confuses people, but it doesn’t change the ampacity. The first figure is the gauge (12AWG). The second figure shows the number of conductors in the wire, not including the bare ground wire. In this case, you have two 12-gauge conductors. You treat 12/2 and 12AWG similarly when determining the ampacity and wattage.

How Many Amps Will 12/2 Wire Carry?

People associate 12/2 with 20A circuits because they can withstand 25 amps at 60 degrees C. However, at 90 degrees C, 12/2 wiring can carry 30 amps.

Does this mean 12/2 cables can run a 25A circuit in a home? No, they can’t. You have to keep the 80 percent NEC rule in mind. The 80 percent rule limits 12/2 wiring to 20 amps.

Therefore, you should connect 12/2 wires to 20A circuits and applications. Although some contractors pair 12-gauge wiring with 15A circuits. This practice is wasteful because 14-gauge conductors, which are cheaper, can carry 15 amps.

What Is 12-2 Wire Used For?

People associate 12-2 wiring with lower-level electrical loads such as alarm clocks, lights, and outlets.

Don’t forget that 12-2 wiring works with 20A circuits, and most homes use 15 and 20A circuits. Therefore, electricians expect this wire size to accommodate most household tools and appliances.

Technically, you can connect as many outlets as you want to a 20A circuit with 12/2 wiring. However, the 1.5A per outlet rule will technically limit you to ten receptacles. Interestingly, many people use 14/2 instead of 12/2.

This substitution is acceptable if you have a 15A circuit. 14/2 cabling performs a similar function as 12/2. At the very least, it will run your home’s lights and outlets. If you compare the two, 12/2 comes out on top. Although, you can understand why some people prefer 14/2:

  • If you follow the 1.5A per outlet rule, 14/2 wires on a 15A circuit will only accommodate eight receptacles instead of the ten you find on a 20A circuit (12/2).
  • 12/2 offers greater versatility because it runs both 15A and 20A circuits. On the other hand, connecting 14/2 to a 20A circuit is an illegal act.
  • You are less likely to overload or overheat 12/2 wiring.
  • 12/2 can safely run every appliance in your home, including powerful devices like air conditioners.
  • 14/2 is cheaper, which makes sense. 12/2 has superior conductivity and durability. Therefore, it commands a higher price tag.

If you have a simple home with basic lighting requirements and primarily light-duty appliances, you can replace 12/2 with 14/2. The practice is risky where 20A circuits are concerned, but that has not stopped homeowners from using 14/2 wiring, specifically because the gauge is cheaper.

But if you want a wire size you can trust to accommodate your home’s electrical requirements without overloading and starting a fire, 12/2 is the best option.

Factors That Affect 12/2 Wire Amps

1). Temperature

High temperatures have a somewhat contentious relationship with metallic objects. This MAST (Materials Science and Technology Teacher’s Workshop) experiment proves that high temperatures increase resistance in electrical materials.

High temperatures increase the number of collisions between valence electrons and vibrating ions, which, in turn, disrupts the motion of the valence electrons. As a result, the current reduces.

What does this mean for 12/2 wiring? When the temperature increases, the conductor’s current-carrying capacity decreases. Additionally, contractors respond to high ambient temperatures by reducing the size of the load a 12/2 cable must carry.

This is because wires already generate heat when they transmit electricity. Placing those wires in a dangerously hot environment increases the chances of overheating. Overheating in a 12/2 cable can melt the insulation and start a fire.

This is why contractors emphasize the setting when wiring a circuit. Cables in the air and above ground have a higher current-carrying capacity because they can dissipate excess heat.

Because ventilation is poor, conductors running through walls and underground have a lower current-carrying capacity. You can’t afford to overwhelm them with heavy loads because they can overheat.

The cheaper option for contractors is to take deliberate steps to limit a wire’s load based on the ambient temperature. However, you can also select wires whose temperature rating matches the environment.

Wires with a higher temperature rating have a higher current-carrying capacity. For instance, 12/2 wiring can tolerate 30 amps at 90 degrees C. Surprisingly, low temperatures don’t affect the amperage. Cold weather is primarily a threat to the cable’s health.

Besides reducing a wire’s performance, cold temperatures lower the conductor’s flexibility. It becomes stiff enough to break.

2). Distance

Some contractors will tell you that length and amperage are not connected, but that is not entirely true. The length can indirectly influence the amps. On the surface, the length primarily shapes the voltage drop.

This is because increasing the length will also raise the resistance. Every conductor resists the flow of current. In other words, every line has some voltage drop. The voltage drop refers to a reduction in a cable’s electrical potential.

Any voltage drop lower than 3 percent is okay. You can run your application without recording any noticeable deterioration in performance. Things become tricky when you elevate the length. The resistance will increase to a point where the voltage drop becomes challenging.

First of all, the higher the resistance, the more heat a cable will generate. Secondly, your appliances may not work because the voltage drop is too high. And if they work, the devices may burn out because they must work harder to compensate for the consequences of the voltage drop.

But how does this affect the amps? You can lower the voltage drop in a long cable by increasing the gauge. According to the physics classroom, wider wires have a lower resistance. If you increase the gauge, the amps will also go up.

In the case of 12/2, moving up to 10/2 will raise the current-carrying capacity to 30 amps. Changes in a 12/2 wire’s voltage drop occur as you increase the length/distance.

3). Material Used

When shopping for 12/2 wires, your retailer will ask you to choose between copper and aluminum. This is because copper has a higher current-carrying capacity than aluminum. You need 10/2 aluminum to replace a 12/2 copper line.

12AWG copper wire can handle 25 amps at 60 degrees C. On the other hand, 12AWG aluminum will only tolerate 20 amps at the same temperature rating.

4). Load

The load size will determine the volume of current passing through an electrical line at any given moment. For instance, 12/2 wiring can withstand 20A. But that doesn’t mean it will transmit 20 amps at all times.

If an appliance only requires ten amps, the 12/2 conductor will carry those ten amps. Some devices use more electricity when they cycle on. This makes them dangerous because they can overwhelm a 12/2 line even though they use less than 20 amps during normal operations.

5). Stranded VS Solid

A stranded wire carries less current because it is thinner, resulting in more air gaps. Additionally, the individual strands have a greater surface area.

12-2 Wire Watt Rating


12-2 wires can carry 20 amps. You get watts when you multiply the amps and volts. Therefore, 20 amps X 120V gives you 2,400 watts. If you change the voltage to 240V, you get 4,800 watts.

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