Triumvirate

The Triumvirate is a Legendary Source for the in Diablo III. It requires character level 60 to drop.

As of patch 2.2.0, it gained a unique affix that greatly boosts the Arcane Orb in tandem with Electrocute, Magic Missile, Spectral Blade or Shock Pulse. The stacks generated by Triumvirate are not consumed upon cast, and refresh with each application. This Source is especially deadly when combined with Delsere's Magnum Opus and Unstable Scepter. Stacks are granted on cast, even if that cast does not hit an enemy.

Originally, it used to offer the highest bonus (excluding Firebird's Eye) to elemental skill damage, Arcane, Fire and Lightning at once, having more Primary affixes than permitted. For non-Cold, non-Magic Missile Wizards, it would be arguably the best choice if they do not have a set Source to equip in the off-hand.