Why does only half of my electrical outlet work?

When only one plug receptacle on a duplex wall outlet works while the other half remains dead, the malfunction is typically caused by a broken internal contact tab or a split-circuit wiring setup. In many residential kitchens, bathrooms, and dining areas, duplex outlets are wired as split-circuits where the small brass break-off tab connecting the top and bottom hot terminal screws is intentionally removed so each half can be controlled independently by separate switches or circuits. Alternatively, physical wear can break an internal spring contact inside one half. You can troubleshoot split-circuit wiring safely by isolating power at the circuit breaker. You can verify that your corrective action is successful when removing the wall plate, checking the brass tab, and replacing a damaged receptacle restores full power to both plug slots.