I installed a new outlet tonight for a 230/208v 15 amp window air conditioner. I used romex 12/2, a 15amp 250v outlet and a double pole 240 breaker(GE). Once everything was wired and connected(before the A/C unit was connected) I turned the power back on and the breaker tripped immediately. I reset it and it tripped again. What did I do wrong or is there a possibility of faulty equipment?