wiring a 30 Amp Power Outlet 30A Circuit Breaker {{UPDATE}}

As others have said, it's going to be prewired (as are the 50/100A panels).

FWIW, I am running 10 awg Romex for 125' to my 30A outlet and then I use a 50' 10awg extension cord. I loose 2~3 volts at full power (leaving me 116VAC or more). So personally, I would just use the standard 10awg Romex unless your voltage at the panel is very low.