Mike, Your right its not just a double up of current rating, Need to apply a grouping factor quite rigidly as both cables would be carrying equal current and subject to simultaneouse overload condition. Believe its also important that both cables are of equal length otherwise Earth loop impedance calcs get screwed up! Have used paralell cables in the past but cheated I have always used a computer program and had it verified by cable manufacturer,s.
Put some details up Mike and lets see what we can come up with. Whats the CPD? Length of run? Installation Method? Max ambient Temperature?
