It seems that using #8 wire for 50 Amp breakers is a common practice when so many electrical charts say #6 wire should be used. Any rule of thumb pointers out there for the inspection or report? Thanks.
It also depends on the application. #8 on a 50 amp feeding an HVAC unit or a motor would likely be code compliant.
Although their conductors are rated for 90° C, for NM cable, SE cable, or AC cable embedded in insulation, you must use the 60° C column of NEC Table 310.16 to find their ampacity. The requirements for interior SE cable installations in Article 338 send you over to Article 334 (NM cable) to determine their ampacity.
I’m not an HI so I will defer to Joe’s advice. However, for an AC unit the conductor size does not have to match the circuit breaker size. You would need to know the Minimum Circuit Ampacity (MCA) of the unit and the Maximum CB or Fuse size. This information is listed on the nameplate of the unit. The conductors are sized according to the MCA and they can be protected by any size OCPD from the MCA up to the maximum. Take a look at the example nameplate below. [MCA 23.3 amps, Max fuse or CB 30 amps]. It would be permissible to have #12 conductors protected by a 30 amp CB or fuse.
