I recently got a bid from an A/C guy to install a RHEEM RA1436WJ1NA 3 ton 14 seer unit. He says the permit will require a 10/3 30 amp circuit to the disconnect. Since I am the one running the circuit.....I understand the #10 and 30 amp DP, but why do I need a neutral.....10/2 w ground is correct is it not? Why run a 10/3 only to cap the neutral at each end? thanks in advance