CirTec is a magic Runeword created by combining a Cir Rune of Ritual and a Tec Rune of Invocation.
How to Create CirTec
You can create CirTec by adding the magic Cir Rune of Ritual and the magic Tec Rune of Invocation to a two-socketed Helm, Chest Armor, Pants, or Two-Handed Weapon.
Cir - Cast the same non-Channeled Skill 3 times in a row. (50)
Tec - Invoke the Barbarian's Earthquake, dealing damage to enemies within. (100)
Overflow
CirTec can not overflow because the amount of Offering you receive from the Cir Rune exactly fills the required Offering of the Tec Rune.
Overflow occurs when your Ritual generates more Offering than required for the Invocation. The overflow effect is proportional to the amount Offering overflows.