Maximum Ampacities for Wire

Maximum Ampacities for Wire

The following table shows the allowable ampacities of conductors (wires) in conduit, raceway, cable or directly buried, based on ambient temperature of 30 degrees Celsius (86 degrees Fahrenheit).  National Electrical Code (NEC) allows rounding up cable ampacity to next size standard fuse or breaker.

Wire Size Copper Conductor Temp Rating Aluminum Conductor Temp Rating
75 Degrees Celsius (167 Degrees Fahrenheit) 90 Degrees Celsius (194 Degrees Fahrenheit) 75 Degrees Celsius (167 Degrees Fahrenheit) 90 Degrees Celsius (194 Degrees Fahrenheit)
*14 20 25
*12 25 30 20 25
*10 35 40 30 35
8 50 55 40 45
6 65 75 50 60
4 85 95 65 75
2 115 130 90 100
1 130 150 100 115
1/0 150 170 120 135
2/0 175 195 135 150
3/0 200 225 155 175
4/0 230 260 180 205
  • NEC specifies that the overcurrent protection device not exceed 30A for 10 AWG wire, 20A for 12 AWG wire and 15A for 14 AWG wire.

For ambient temperatures above, multiply the allowable ampacities by  the correction factor listed under the insulation temperature rating below:

Temperature range 75 Degrees Fahrenheit Insulation 90 Degrees Fahrenheit Insulation
31-35 Degrees Celsius 87-95 Degrees Fahrenheit 0.94 0.96
36-40 Degrees Celsius 96-104 Degrees Fahrenheit 0.88 0.91
41-45 Degrees Celsius 105-113 Degrees Fahrenheit 0.82 0.87
46-50 Degrees Celsius 114-122 Degrees Fahrenheit 0.75 0.82
51-55 Degrees Celsius 123-131 Degrees Fahrenheit 0.67 0.76
56-60 Degrees Celsius 132-140 Degrees Fahrenheit 0.58 0.71

Recommended Inverter Cable and Overcurrent Protection

Use this table to decide cable size and fuse or breaker size for common inverter models.  Smaller cable sizes can be used if fuse or breaker size is reduced but this can cause problems if the inverter is run near its maximum output wattage.  Larger cables may be necessary if the distance from the inverter to the battery is greater than 10 feet.

Inverter Voltage Continuous Watts Maximum Inverter Input Amps Fuse Size (amps) Circuit Breaker (amps) Wire Size (AWG)
12 Volt 600
800
1000
1500
2400
2500
2800
3000
80
107
134
200
320
334
382
400
80
110
200
300
400
400
400
400
80
110
175
250
250
250
250
250
2
2
2/0
4/0
4/0
4/0
4/0
4/0
24 Volt 600
800
1000
1500
2400
2500
3000
3500
4000
40
54
67
100
160
167
200
230
265
50
75
80
110
200
200
300
300
300
50
75
100
110
175
175
250
250
250
8
4
2
2/0
2/0
2/0
4/0
4/0
4/0
48Volt 3000
3600
4000
5500
76
90
148
185
110
110
200
400
110
110
175
250
2/0
2/0
2/0
4/0

For more info and recommendations so on pairing the right fuse and cables to your DC to AC power inverter, watch Jeff’s YouTube video below.

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5 Responses to Maximum Ampacities for Wire

  1. Edgar Acosta says:

    Hi Jeff
    Been watching your videos for a few years and you do put out a lot of practical info out there.
    Currently thinking on working on hydro system using one of your pmg 3 phase generators my question is and since your units are really for wind power how do I figure out that rpm say at 40mpg, since I really need is rpm, and not wind speed
    Not sure I’m clear on my question.
    Say for example at 40 miles a hour you pmg is producing 3500 watt what I need is the rpm for that wind speed.
    Hope you can answer my question
    Thanks
    Edgar Acosta

    • crystal says:

      Hi Edgar, thanks for supporting us on YouTube. We appreciate it! The PMGs are great for hydro use and we have hydro configurations for both the 1600 watt and 2000 watt models.

      Shoot us an e-mail over to sales@mwands.com and we’ll get the RPM values for you.

  2. Jose Santiago says:

    Hi, Jeff
    For reasons of safety my turbine ( Freedom PGM 1600w 24v) I have to install about 70′ to 75′ away from the batteries , I have doubts if should keep the cable 10 or increase it to cable 8 by the distance and by temperature although the cable is through conduit, thank for your help.

  3. Wilfred porter says:

    Recently purchased the 24 volt Rebel wind Generator, on examination I could feel a rough not smooth resistance when rotating the PMG. Is that normal

  4. Mike Bearden says:

    I’m confused about the difference in the maximum allowable ampacity of #2 awg vs. #2 welding wire for powering the inverter. Is not welding wire a higher amp rating? Could you clarify? Thank you

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