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1) The National Electrical Code recommends that the voltage drop be less than 3% over the distance of the run.
2) Using 190 feet with 10 AWG Stranded copper conductors at a 30 amp load with 240 volts results in a 13.7 voltage drop or a 5.7% which is not acceptable.
3) Using 190 feet with 8 AWG Stranded copper conductors at a 30 amp load with 240 volts results in a 8.6 voltage drop or a 3.6 % voltage drop which is also not acceptable.
4) Using 190 feet with 6 AWG Stranded copper conductors at a 30 amp load with 240 volts results in a 5.4 voltage drop or a 2.3% voltage drop which is acceptable.
5) Using 190 feet with 6 AWG Stranded copper conductors at a 40 amp load with 240 volts results in a 7.2 voltage drop or a 3% voltage drop which is acceptable.
6) The condensers will have a "Minimum Circuit Ampacity (MCA)" rating on the nameplate of the condenser which I assume is the 30 amp value.
Therefore, due to the length of the run being 190 feet, the branch circuit conductors need to be sized as 6 AWG Stranded copper using a 30 amp double pole circuit breaker in order to satisfy the National Electrical Code recommendation.
Remember, that a 30 amp breaker calls for a minimum of 10 AWG conductors, but since the run length is long (190 feet) you have more resistance per foot in a 10 AWG conductor versus a 6 AWG conductor. The thicker the conductor, the less resistance per foot, thus the less voltage drop in order to agree with the NEC 3% recommendation.
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