Report 15 foot rule? In Electrical Questions Posted November 24, 2010 I think he meant the 10-ft feeder tap rule [240.21((1)] — You don't have to install an OCPD at the tap point of a feeder tap if its length doesn't exceed 10 ft and if it meets the following requirements: The ampacity of the tap conductor is not less than the computed load in accordance with Art. 220, and not less than the rating of the device supplied by the tap conductors or the OCPD at the termination of the tap conductors. The tap conductors aren't extended beyond the equipment they supply. The tap conductors are installed in a raceway if they leave the enclosure. The tap conductors have an ampacity of no less than 10% of the ampacity of the OCPD from which the conductors are tapped. You would still need 100A (like your #2) rated wire for the 100A sub-panel or put a 50A main in the sub-panel and use the #8.