Passive tree node: What does "Endless Circuit" do? Does it interact with Cast when Shock?

So I've been having fun with Invoker and this node really get me confused.

"25% chance on Consuming a Shock on an Enemy to reapply it"

I get the roughly idea that it gives 25% chance to reapply shock.
What I don't understand is that, do you required to have some way to actively consume shock (ie: Siphoning Strike), so you can trigger this node?
Or you just gain the ability to consume shock for all attacks after you get this node?

Also, does reapplying shock this way gives energy to Cast when Shock?

Lightning Conduit (last Lightning gem on the sorc tree) consumes shocks.