The added cooldown portion is NOT added on top of the trigger cooldown
Cast while Channelling does not have a cooldown to add to, so the cast time adds to 0 seconds and results in a total cooldown time exactly matching the cast time (assuming no modifiers to cooldown recovery rate).
Cast while Channelling tries to trigger the spell every 0.x seconds while you channel. If the skill is on cooldown at that time, that will fail.
If the cast time (and thus cooldown) of Lightning Conduit is shorter than the time between attempted CwC triggers, it will trigger at the CwC trigger rate, because each time CwC tries to trigger it, it will be off cooldown and ready to go..
If the cast time (and thus cooldown) of Lightning Conduit is longer than the time between attempted CwC triggers (but shorter than twice that time), it will trigger at half CwC trigger rate, because every second time CwC tries to trigger it, it will ...
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