The 3 A per-contact current rating is the maximum at 25°C ambient with all circuits loaded. Above 85°C ambient, derate per the standard AMPMODU curve.
Board-to-Board or Cable — What This Header Connects To
This is an unshrouded breakaway header, style listed as Board to Board or Cable. For board-to-board stacking, the 0.318" (8.08mm) mating pin length and 0.090" (2.29mm) insulation height give a mated stack height around 0.408" (10.37mm) plus the receptacle body. For wire-to-board, use the matching crimp receptacle and housing.
For a pin-compatible alternative within the same series, check the 6-146277-5 variant (typically tin-plated mating surface, lower cycle life).