Re: 600Amp. 120/240v service entrance
If the total calculated load is 510 amps or lower (i.e., twice the 255 amp rating at 75C), yes. Otherwise, no. Furthermore, if you don't have a calculation (or other evidence) that shows the load to be below the 600 amp setpoint of the overcurrent protection, then you need conductors rated for every bit of that 600 amps. That would be a minimum of a pair of 350's.