Electric Coils (as named in the Metroid Prime 2: Echoes internal data) are conduits of electrical energy present in the Sanctuary Fortress. They are connected to an energy system that powers the Dynamo Works, although they also obstruct progression by bioforms small enough to fit into the maze portion of the Works. The coils are extremely hazardous to such bioforms.
Samus Aran uses the coils against the Spider Guardian during the battle with it. Using its Spider Ball powers against it, Samus is required to stun the creature using her Bombs until the Spider Guardian's movement is slowed down and it flashes green. She has a limited amount of time to activate a Bomb Slot that alters the course of the Spider Guardian, and leads it straight into an Electric Coil. The coils are destroyed as the Spider Guardian touches it, and it moves further into the Works. This process is repeated twice, until Samus enters the fourth phase of the battle where she is required to drive the Guardian into three coils. Once it is electrocuted by the final coil, the Guardian dies and releases the Spider Ball for Samus to recollect after it was stolen from her by the Ing.
If Samus Sequence Breaks to acquire a Power Bomb before fighting its Guardian, and uses one on the Spider Guardian, it will instantly destroy the creature but not the Electric Coils, leaving her trapped in the Dynamo Works unless the game file is restarted.