Unfortunately elemental equilibrium doesn't work that way (it is not explained very clearly in the game). When you have EE and hit an enemy with an attack, they gain +25% resistance to each element you hit them with and -50% resist to each element that you did not hit them with. The buff lasts 5 seconds or until the next EE buff is applied.
If you hit them with fire only, they get:
+25% resist fire
-50% resist lightning
-50% resist cold
If you hit them with fire and cold (but not lightning), they get:
+25% resist fire
+25% resist cold
-50% resist lightning
The way to get the benefit is to alternate hits. If you go fire->lightning->fire->lightning then each hit after the first will get the benefit of -50% resists.
Sadly, if you hit with all 3 elements it doesn't do you any good at all, they get this...
+25% resist fire
+25% resist cold
+25% resist lightning
... because there are no elements that you didn't hit them with, so they get no -50% buffs.
Also worth noting is that totem abilities do trigger EE and minion attacks do not trigger EE.
The wiki description is actually correct right now, based on current dev posts:
http://en.pathofexilewiki.com/wiki/E...al_Equilibrium