Sizing wire and circuit breaker for air conditioner

[Carultch]

If you have a 45 amp breaker you need wire that can handle 45 amps you cannot put 10 nm on a 45 amp breaker put the 30 amp breaker in with 10 wire if anything


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You generally select the largest permissible OCPD, to avoid nuisance tripping. If you are uncomfortable with the special exception for HVAC equipment, increase the wire size to match the maximum circuit breaker, rather than the other way around. Not that you have to do this, as the code is clear that the unit's nameplate overrides the general NEC rules for the relationship between OCPD and circuit amps. Obviously, if you are an inspector, you can't call it a violation when there is no doubt that the installer followed the rules as written.

As others have said, HVAC equipment is a special case that deviates from standard Article 240 rules for overcurrent protection, typically due to the unit having internal overload protection.