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Wire Heat Ratings


It's The Law
The Code of Federal Regulations (CFR) 183.425 Conductors

Except for intermittent surges each conductor must not carry a current greater than that specified in Table E for the conductor’s gauge and temperature rating.
For conductors in engine spaces, amperages must be corrected by the appropriate correction factor in note 1 of Table E.

Due to engine heat, the ambient temperature in engine spaces is usually higher than in other spaces of the boat. Wiring in and passing through engine spaces must be able to operate at these higher ambient temperatures. The ampacity values in Table E are based on an ambient temperature of 30° C (86° F) which is considered reasonable for use on boats except in engine spaces. The correction factors in Note 1 in Table E convert the ampacities to Table E to acceptable values in an ambient temperature of 50° C (122° F). This higher temperature has been selected as satisfactory for engine spaces. Note 1 is supplied to eliminate the need for calculating the corrections to Table E. The values are already corrected.

Table E: Temperature Rating of Conductor Insulation

Conductor Ampacity Outside Ampacity Inside
of Engine Space
Size (AWG) of Engine Space (Note 1)
18 20 17
16 25 21
14 35 30
12 45 38
10 60 51
8 80 68
6 120 102
4 160 136
3 180 153
2 210 178
1 245 208
1/0 285 242
2/0 330 280
3/0 385 327
4/0 445 378

*De-rating for engine space is 0.85 for 105° C (221° F) rated wire.

Original article from Marinco website

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