Primus Conduit - Revisited (From RK Wiki)
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The Primus Conduit can increase the firing rate of the following defenses
Watch Tower
Spell Tower
Catapult (increases attack speed)
Sky Watcher
Bunker (reduces cooldown)
Arrow Launcher
Flare Tower
If you dont see the rays of light jumping out from a conduit, it isn´t working right (not connected). Don't waste this valuable asset of your defense. Use it wisely.
Catapult Level 5 Connected and Not Connected Numbers
Watch Tower Level 8 Connected and Not Connected Numbers
Placement of Conduit
Defenses must directly connect to at least 2 tiles of the Primus Conduit edge in order to receive the increase. You can connect a defense to 2 Primus Conduits at the same time, which will give you a multiplied increase in fire speed.
Catapult is boosted by 2 Primus Conduits (charged amount is multiplied by 2 conduits)
Partly taken from here