What is the amp rating for 12 gauge wire?

The amp rating of 12-gauge copper wire with insulation type TW/UF is 20 amps at 60°C (140°F). It is recommended that you connect a total load of 1920 Watts (80%) for safety purposes  though it can carry a maximum load of 2,400 Watts at 120 V. 

For aluminum wire, the amp rating is lower at 15 amps. You normally find this wire size in residences where it is often used to connect small appliances like light fixtures and household receptacles.

Is this amp rating for 12-gauge copper wire fixed?

Type of insulation used

The amp rating is not fixed and instead depends on the type of insulation used. When heat resistant insulation is used for example, 12-gauge wire can carry higher amp ratings safely.

For example, the amp rating of 12-gauge wire using THHW, THW, THWN, XHHW, USE, ZW insulation types is 25 amps and 30 amps with THHN, THHW, THW-2 insulation.

So, while 12-gauge wire is commonly taken to carry 20 amps, don’t take this as a rule of thumb, always check the technical specifications of the wire or cable first for the safety of your installation.

Ambient temperature

Besides the type of insulation used, the ambient temperature will also affect how much current the wire can carry.

Higher ambient temperatures will require that:

  • you lower the current  that the cable uses or
  • you can simply use a more heat tolerant wire to  main the current level.

The table below shows the correction factors that can be used to adjust the current level when the  ambient temperature differs from 30°C (86°F): Source: NEC 2017.

Ambient temperature (°C)Conductor temperature 60°CConductor temperature 75°CConductor temperature 90°CAmbient Temperature (°F)
10 or less1.291.21.1550 or less
11–151.221.151.1251–59
16–201.151.111.0860–68
21–251.081.051.0469–77
26–3011178–86
31–350.910.940.9687–95
36–400.820.880.9196–104
41–450.710.820.87105–113
46–500.580.750.82114–122
51–550.410.670.76123–131
56–60 0.580.71132–140
61–65 0.470.65141–149
66–70 0.330.58150–158
71–75  0.5159–167
76–80  0.41168–176
81–85  0.29177–185

Related questions

1. What is the amp rating for 14 gauge wire?

The amp rating of 14-gauge copper  wire with insulation type TW/UF is 15 amps at 60°C (140°F). You should  connect a recommended total load of 1,440 Watts (80%) for safety purposes  though it can carry a maximum load of 1,800 Watts at 120 V.

You normally find this wire size in residences where it is often used to connect small appliances like light fixtures and household receptacles.

2. What is the amp rating for 10 gauge wire?

The amp rating of 10-gauge copper  wire with insulation type TW/UF is 30 amps at 60°C (140°F). You should connect a recommended total load of 2,880 Watts (80%) for safety purposes  though it can carry a maximum load of 3,600 Watts at 120 V.

For aluminum wire, the amp rating is lower at 25 amps.

You can choose to use 240V and in this case, the recommended load (80%) is 5,760 Watts with a  maximum load with 7,200 Watts.

10-gauge wire is commonly used for window air-conditioners and clothes dryers.

3. What is the amp rating for 8 gauge wire?

The amp rating of 8-gauge copper  wire with insulation type TW/UF is 40 amps at 60°C (140°F). You should  connect a recommended total load of 7,680 Watts (80%) for safety purposes  though it can carry a maximum load of 9,600 Watts at 240 V.

For aluminum wire, the amp rating is lower at 35 amps.

8-gauge wire is commonly used for electric stoves and central air conditioners.

4. What is the amp rating for 6 gauge wire?

The amp rating of 6-gauge copper  wire with insulation type TW/UF is 55 amps at 60°C (140°F). You should connect a recommended total load of 10,560 Watts (80%) for safety purposes  though it can carry a maximum load of 13,200 Watts at 120 V.

For aluminum wire, the amp rating is lower at 40 amps.

6-gauge wire is often used to connect large appliances like central air conditioning and electric furnaces.

You can also use the calculator below to obtain indicative amp rating values for both copper and aluminum wires.

Amp rating calculator for wire gauges: 18-2000 

You can use this handy calculator  to easily find the amp rating of wire gauges: 18-2000. These amp ratings are based on the National Electric Code, 2017,  Table 310.15(B) (16).

Note:

  • This calculator results are indicative and should only be used as a guide. Always consult a qualified professional when designing your applications.
  • This is for Insulation types TW/UF. Based on Ambient Temperature of 30°C (86°F) and conductor temperature of 60°C (140°F).

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