The arm has 8 slots, so pre-civil war, there was no way to add more than 2. However this was overlooked so far in the PTS. The slot where the third energy port is has not been upgraded to render a ppc weapon, therefore, even if you have 3 ppc's slotted in that arm, and even though it shows 3 ppcs on the weapon groups tab; when you enter a game, there are only 2 ppcs in your loadout.
This also yields some bugs while saving your loadout, as the game is conflicted in how many ppc's you have.
Edit- My bad there is another topic stating the same information.
Edited by VESSILY, 04 July 2017 - 11:37 AM.