Overload enchantment

Overload enchantments are enchantments that fit in their own personal enchantment slot called Overload Slots, were introduced in Module 3: Curse of Icewind Dale.

Overload enchantments cannot be refined, and vanish when their timers run out. The timer runs only in-combat.

Overload slots are found on most Head and Arms pieces.

In Module 6: Elemental Evil, and 7: Strongholds additional armors were introduced that also hold overload slots in Head and Arms pieces, and Companion Only equipment with overload slots

Also introduced in Strongholds were Slayer and Ward enchantments that cause you to deal extra damage / take less damage from a specific class of enemy.

Black Ice Enchantments
Black ice overload enchantments are earned from Kessell's Retreat reward chests, and from Icewind Dale Campaign task Black Ice Enchantments. Also you can craft them at the Black Ice Forge within Caer-Konig.
 * Used to be crafted in Black Ice Shaping in order to make lesser and greater versions until it was discontinued.

Draconic Glyph Enchantments
Lesser Draconic Glyphs are quite rare, only coming from Dragon Scale Merchant within Protector's Enclave, and Siege of Neverwinter merchant Siege Defense Coordinator. Greater Draconic Glyphs are obtained from The Shores of Tuern Skirmish, Lair of Lostmauth Dungeon, and Rise of Tiamat Trial.

Hell Pit Enchantments
Hell Pit overload enchantments are purchased with within the Challenge Tab from Soul Collector event store merchant during the Hell Pit event.

Slayer Enchantments
Slayer Enchantments can be bought at The Gemmonger in the Guild Stronghold Marketplace. There are player enchantments and companion only enchantments, with a rank 1 and rank 2 varieties.

Ward Enchantments
Ward Enchantments can be bought at The Gemmonger in the Guild Stronghold Marketplace. There are player enchantments and companion only enchantments, with a rank 1 and rank 2 varieties.