Section Index Owatonna Steele County Amateur Radio 20-Jul-2007

Wire Ampacity

Sources NFPA 79
Industrial Machinery
NFPA 70
National Electrical Code
Temp
Rating
60 C 75 C Inside
Enclosure
THHN
90 C
THWN
75 C
RUW
60 C
28 - 0.8 0.8 - - -
26 - 1 1 - - -
24 2 2 2 - - -
22 3 3 3 - - -
20 5 5 5 - - -
18 7 7 7 14 - -
16 10 10 10 18 - -
14 15 15 20 25* 20* 20*
12 20 20 25 30* 25* 25*
10 30 30 40 40* 30* 30*
8 40 50 60 55 50 40
6 55 65 80 75 65 55
4 70 85 105 95 85 70
2 95 115 140 130 115 95
*The load current an overcurrent protection shall not exceed 15amps for 14 AWG, 20 amps for 12 AWG, and 30 amps for 10 AWG copper.

NEC 310 Notes to Tables 310-16 through 310-318

Where the number of conductors in a raceway or cable exceed three, the ampacities given shall be reduced as shown in the following table. In addition, other derating factors (e.g., temperature) must be applied. Number of Conductors Percent of Values in Table (above)
4 thru 6 80
7 thru 9 70
10 thru 24 * 70
25 thru 42 * 60
43 and above * 50
* These factors include the effects of a load diversity of 50 percent.


Flexible Cords and Cables

No. of Current
Carrying Conductors
Wire Size - AWG
18 16 14 12 10 8 6 4 2
3 710 15 20 25 35 45 60 80
2 1013 18 25 30 40 55 70 95

NEC 240-4
Flexible cord, including tinsel cord and extension cords, shall be protected against overcurrent in accordance with their ampacities as specified in Table 400-5.

Exception No.1: When a flexible cord or tinsel cord approved for and used with a listed appliance or portable lamp is connected to a branch circuit of Article 210 in accordance with the following:

  • 20 ampere circuits, tinsel cord or No. 28 cord and larger.
  • 30 ampere circuits, No. 16 cord and larger.
Exception No.3: Flexible cord used in tested extension cord sets having No. 16 AWG or larger conductors shall be considered to be protected by 20-ampere branch-circuit overcurrent protection.

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