Multiple EE strikes will overwrite each other. The effect lasts 5 seconds or until being overwritten.
If you hit an enemy with two different elements at the same time it will give -50% Resistance to third element and +25% to both elements used. A hit carrying all three elements types will give +25% to all elemental Resistances.
Totem skills trigger EE as they are treated as your hits. Minion's hits do not count as yours so do not trigger EE.
Multiple attacks that hit simultaneously are still processed independently, so the first hit that is processed will trigger EE that affects the other hits. 
As long as you are careful to not use the same element twice in a row, EE can greatly boost damage. Try to use a combination of skills that alternates between two elements or cycles through all three:
- + is a basic example
- An area skill like sets up enemies for a high-damage skill like
- Use two gems and link each to , , or
Elemental Equilibrium is located in the center of the tree, just above the Scion's starting area.
|Class||Distance from start|
- Chris (January 23, 2013 2:31 AM). "0.10.0 Patch Notes". Official Path of Exile Forum. Retrieved July 27, 2013.
- Mark_GGG (July 16, 2012 3:30 AM). "Elemental Equilibrium". Official Path of Exile Forum. Retrieved April 2, 2013.
- Mark_GGG (July 10, 2014 5:45 PM). "Mechanics Question: Elemental Equilibrium and Remote Mines". Official Path of Exile Forum. Retrieved August 24, 2014.