The most popular single conductor copper wire we carry is #8 gauge THHN Copper Stranded Wire, which is RATED FOR 55 AMPS @ 90 deg C. (150 deg F.) BUT IT CAN HANDLE MUCH MORE THAN THAT IF YOU USE PROPER CONDUCTIVITY LIMITS.

If you were to hook this up in parallel with another similar wire then you could probably handle a current of about 100 amps before you need to worry about it. But why would you want to do that? This figure is based on the assumption that both wires are being used at their maximum capacity all the time, which is very unlikely if you use them for **different purposes**. If one or other of these wires gets overloaded then it could fail by burning or melting.

In general, your cable should be able to handle at least as much current as what it's being used for. For example, if you're using it as a hot wire then it should be able to handle at least as much current as a light fixture or heater. And if you plan to use it as a neutral then it should be able to handle at least as much current as any device connected to it.

You should also take into account the fact that I've already mentioned that if one wire gets overloaded then it could fail.

Amp ratings and wire diameter

Copper | ||
---|---|---|

Wire Gauge Size | 60°C (140°F) NM-B, UF-B | 90°C (194°F) THWN-2, THHN, XHHW-2, USE-2 |

14 | 15 | 25 |

12 | 20 | 30 |

10 | 30 | 40 |

Amp ratings and wire size

Copper | Aluminum | |
---|---|---|

Wire Gauge Size | 60°C (140°F) NM-B, UF-B | 90°C (194°F) XHHW-2, THHN, THWN-2 |

14 | 15 | — |

12 | 20 | 25 |

10 | 30 | 35 |

Amp ratings and wire diameter

Copper | Aluminum | |
---|---|---|

Wire Gauge Size | 60°C (140°F) NM-B, UF-B | 75°C (167°F) THW, THWN, SE, USE, XHHW |

14 | 15 | — |

12 | 20 | 20 |

10 | 30 | 30 |

That's not good. 4th THHN has a maximum current rating of 85 amps at 75 degrees Celsius. This would be for MC cable or raceway conductors. SE cable with **thermal insulation** or NM cable is rated at **60 degrees** Celsius and has a capacity of 70 amps. Kwood (CMI Kevin Wood), March 2, 2012, 11:38 p.m. #3

The ampacity of a conductor is the amount of current it can carry without overheating. The ampacity of a wire is the product of its cross-section and the temperature at which it is used. For example, an AWG 24 copper wire has a current carrying capacity of about 40 amperes at 125 degrees Fahrenheit; 80 ampeers at **200 degrees F**; and 120 ampeers at 250 degrees F.

The voltage across a resistance is equal to the RMS value of the current through it. So, if you know the RMS value of the current drawn by your household appliances, you can calculate the resistance needed in order to avoid exceeding any specified limit. For example, an electric stove uses about 15 amps at 120 volts, so it needs a 20-amp breaker. A refrigerator/freezer takes about 12 amps at 240 volts, so it needs a 30-amp breaker. If you have a five-piece suite with each piece drawing two amps, then you need a 20-amp breaker.

Amperage and wire size ratings

Wire Size | 75°C (167°F) | |
---|---|---|

AWG | (mm²) | Copper |

8 | (8.4) | 50 |

6 | (13.3) | 65 |

4 | (21.2) | 85 |

"Twelve-gauge wire can handle 20 amps, 10-gauge wire can handle 30 amps, 8-gauge wire can handle 40 amps, and 6-gauge wire can handle 55 amps," and "The circuit breaker or fuse is always sized to protect the conductor [wire]."

So if you're wiring a house, unless you know **exactly what** you're doing it's usually best to use 12-gauge wire for circuits requiring more than 20 amps. If you go any smaller than 12-gauge, you're putting yourself at risk of burning up your wire too soon before you reach every outlet in **your home**. And if you use any larger than 12-gauge, you'll be overloading your circuit breaker/fuse and causing it to trip.