Heater Hookup Wire
The use of this table for establishing ampacity ratings is an inexact procedure. This table should only be used as a starting point when establishing ratings for any given situation. Values may be lesser or greater than those given in the table because of the influence of installation method, environment, number of conductors, conductor composition and size, ambient temperatures, insulation types, etc. It is recommended that design engineers desiring accurate ampacity data closely study the 1990 National Electrical Code Handbook Article 310-15-310-84. Additional information can be derived from AIEE, paper number 57-660, “The calculation of the temperature rise and load capability of cable systems” by J. H. Neher and M. H. McGrath. This paper was presented to the AIEE general meeting in Montreal, Quebec, Canada on June 24-28,1956 and was published in the “AIEE transactions,” part 3 (power apparatus and systems), Volume 76, October, 1957, pp. 752-772.


Conductor Types:
tc = tinned copper
npc = nickel plated copper
npi = nickel plated iron
A-nickel = Type ‘A” 100% nickel

Current Carrying Capacity Base Temperature at 40°C (Values tabulated are In Amperes)
Wire Gage AWG Conductor Type
200°C 250°C 250°C 250°C 450°C 450°C
tc,npc npc-7% A-nickel npi npc-27% A-nickel
24
7.2
8.0
4.0
3.3
9.0
4.3
22
9.6
10.8
5.0
4.4
12.0
5.6
20
14.0
15.0
7.0
6.0
18.0
8.0
18
18.0
20.0
9.4
8.0
23.0
11.0
16
24.0
26.0
12.0
11.0
30.0
14.0
14
36.0
39.0
18.0
16.0
45.0
21.0
12
45.0
49.0
23.0
20.0
56.0
26.0
10
60.0
66.0
31.0
27.0
75.0
35.0
8
83.0
91.0
-
-
104.0
49.0
6
110.0
121.0
-
-
138.0
65.0

Temperature Correction Factors For ambient temperatures other than 40°C (104°F), multiply the ampacities shown above by the appropriate factor shown below
Ambient Temperature Wire Temperature Rating
°C °F 200°C 250°C 450°C
41-50
106-122
0.97
0.98
0.99
51-60
124-140
0.94
0.95
0.99
61-70
142-158
0.90
0.93
0.96
71-80
160-176
0.87
0.90
0.95
81-90
177-194
0.83
0.87
0.90
91-100
195-212
0.72
0.85
0.92
101-120
213-248
0.71
0.79
0.89
121-140
249-284
0.61
0.71
0.86
141-160
285-320
0.50
0.65
0.84
161-180
321-356
0.35
0.58
0.81
181-200
357-392
-
0.49
0.78
201-225
393-437
-
0.35
0.74
226-250
439-482
-
-
0.69
251-275
483-527
-
-
0.65
276-300
528-572
-
-
0.60
301-325
573-617
-
-
0.55
326-350
618-662
-
-
0.49
351-375
663-707
-
-
0.42
376-400
708-752
-
-
0.34
Example: The current carrying capacity (ampacity) rating of a 16 AWG 200°C npc conductor at 40°C is 24.0 Amps.

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