When the grounded conductor is to be spliced in a 12-inch by 12-inch junction box, there shall be at least ? of free conductor left for splicing.

6" - 300.14 There should be a  6" free conductor left for splicingWhy there should be 6" splicing?You must leave the junction box with at least six inches of free conductor wiring when running electrical cables from the box to the box for connecting needs.Actually, 6-8 inches can be left when running the electric cables, additionally even if the grounded conductor is to be spliced in a 12-inch by 12-inch.Conductor splicing: A splice, which can be finished using either the crimping or soldering method, is the joining of two or more conductors in a way that produces a permanent electrical termination and mechanical link.Hence we can conclude that 6 inches is fine for the conductor splicing