Suppose we direct-buried some 8 AWG cable. It's now under a parking lot, and retrenching it is out of the question. Now, needs have changed and we need to get 50A out of the circuit, which is possible with 8 AWG in the 75C column. The wire is good for it.

What else is needed to qualify to use the 75C column?

Does anything change if this is wired in the interior of a house?

  • Blacktop parking lots can get extremely hot so hopefully the wire is buried a good depth so as not to be so much affected by the surface temperature. How deep is it? How moist is the soil? – Michael Karas Nov 12 '17 at 1:44
  • What type of cable are we talking about here? UF? direct bury multiplex (USE-2 multiconductor)? direct burial MC? – ThreePhaseEel Jul 17 '19 at 1:30
  • @ThreePhaseEel UF-B. – Harper - Reinstate Monica Jul 17 '19 at 2:05

UF can't beat the heat

Unfortunately for you, UF cable is like NM in that it can't be run at any higher temperatures than 60°C:

340.80 Ampacity. The ampacity of Type UF cable shall be that of 60°C (140°F) conductors in accordance with 310.15.

Now, if this were a tri-rated (USE-2/RHH/RHW-2) multiplex cable, or a direct burial MC cable, it would be something of a different story, but that's beyond the scope of this answer.

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