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# We recently had two air conditioning units installed at our

We recently had two air conditioning units installed at our church. The Installers wanted the electrician to run separate 40 amps lines for each unit. Although the electrician ran the two lines, he used 10/3 and 30 amps breakers. Each 4 ton air unit calls for 30 amps, but each of the 10/3 lines run about 190 feet, so will these units still need 40 amp breakers? Should the electrician have used 8/3 and 40 amp breakers due to the long run?

Hello.....my name is XXXXX XXXXX I will be happy to assist you with your electrical question. My goal is to exceed your expectations on Just Answer!

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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