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How Many Amps is 4 AWG Copper Good for?

Written by Edwin Jones / Fact checked by Andrew Wright

how many amps is 4 awg copper good for

Navigating wire sizing can be either a relatively hassle-free or head-scratching experience. We don’t want you to fall into the latter category as much as possible. So if you’re wondering, “How many amps is 4 awg copper good for?” take time to read this.

The ampacity or current-carrying capacity of 4 AWG copper wires at 75°C (167°F) is 85 amps for THW, THWN, SE, USE, and XHHW wires.

However, when the maximum operating temperature is 60°C (meaning the wire is either NM-B or UF-B), the amperage should not exceed 70, according to the National Electrical Code (NEC).

Fundamental Factors Affecting 4 AWG Copper Ampacity

The ampacity of a 4-gauge wire made from copper depends on several key factors.

1. Operating Temperature

The temperature that the conductor is operating at determines how much current it can handle before overheating. The hotter the wire gets, the lower its amp limit becomes.

Ampacity tables provide ratings based on maximum allowed temperatures like 60°C, 75°C, or 90°C for the conductor, as shown in the table below.

  60°C (140°F)



75°C (167°F)





90°C (194°F)




Amps 70 85 95

2. Ambient Temperature

The temperature of the surrounding environment also matters. The standard ampacity ratings assume an ambient temperature of 30°C (86°F). In warmer environments, the heat dissipation ability drops, requiring lower ampacities to avoid overheating.

The NEC includes correction factors to derate or reduce the ampacity for ambient temperatures above 30°C.

3. Number of Conductors

Bundling conductors together reduces their ability to dissipate heat and lowers the ampacity. The 85 amp 4 AWG copper rating assumes:

  • 1-3 current carrying conductors bundled together
  • If bundled with more than 3 conductors, the ampacity drops to 80 amps
  • Should the bundle exceed 15 conductors, the ampacity is halved, meaning the amp rating is now 42.5.

4. Installation Conditions

Enclosed installations like conduit provide limited air circulation, restricting heat dissipation. Open-air installations allow better cooling and can support higher ampacities.

To Wrap It Up


The standard ampacity rating for #4 copper wire is 85 amps, based on typical assumptions for:

  • 75°C maximum operating temperature
  • 30°C ambient temperature
  • 1-3 current-carrying conductors bundled
  • Open air installation

By optimizing these factors, 4 AWG copper can safely handle a maximum amperage of 95. Adverse conditions may decrease the safe limit to below 85 amps.


How many amps is 4 awg copper good for? In short, 4 AWG copper can safely carry 85 amps of current based on industry standards.

Understanding the factors like temperature and bundling provides flexibility to optimize 4 AWG installations for slightly higher or lower ampacities as needed. We hope our article has helped shed light on this matter for you.

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