User blog comment:Ficus7/Allowed Technology/@comment-24171828-20140913160116/@comment-14850713-20140914174251

The exploding ERA does not deflect an incoming round. A HEAT round works by firing a jet of molten steel into armor, causing it to rupture. The ERA counteracts this using the explosion of the ERA block (triggered when it was hit) to disrupt the jet. The ERA itself is useless against sabot or AP rounds as these will just punch right through. That's why it is always used as an outer layer in conjunction with the main tank armor.