Wire Size & Amp Ratings

  • Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Current is measured in amperes or “amps”. You must use the correct size wire for the current (load) requirement of the circuit to prevent the wire from overheating.
  • The number and type of electrical devices connected to a circuit determine the ampacity requirement of the conductor. Usually, a general purpose house circuit is designed for 20 amps. Lighting circuits may be designed for only 15 amps
  • To calculate the load requirement for a circuit, first add up the wattage of all the electrical devices that will be on the circuit. Then, divide the total wattage by the voltage of the system, typically 120 or 240, and that will give you the required current or amps.
 CopperAluminum
Wire Gauge Size60°C (140°F)
NM-B, UF-B
75°C (167°F)
THW, THWN,
SE, USE, XHHW
90°C (194°F)
THWN-2, THHN,
XHHW-2, USE-2
75°C (167°F)
THW, THWN,
SE, USE, XHHW
90°C (194°F)
XHHW-2, THHN,
THWN-2
14152025------
122025302025
103035403035
84050554045
65565755055
47085956575
3851001157585
29511513090100
1---130145100115
1/0---150170120135
2/0---175195135150
3/0---200225155175
4/0---230260180205
250---255290205230
300---285320230260
350---310350250280
500---380430310350
600---420475340385
750---475535385435
1000---545615445500

WARNING! Installation of electrical wire can be hazardous and, if done improperly can result in personal injury or property damage. For safe wiring practices, consult the National Electrical Code®, your local building inspector, or a qualified electrician.

Ampacities are based on the 2017 NEC and do not reflect any temperature correction or ampacity adjustments that may be required. Please consult a qualified electrician or professional engineer to determine the appropriate values for your specific application.

WHERE TO BUY

Cerrowire markets through a number of quality retailers and manufacturer’s representatives.