Siemens 3UG4511-1AQ20 Monitoring Relay

Siemens 3UG4511-1AQ20 is an analog monitoring relay in the 3UG family designed for phase-sequence monitoring in three-phase power networks, with a continuous operating range of 420 to 690 V AC at 50/60 Hz, making it suitable for high-voltage industrial applications. The unit incorporates a single changeover (SPDT) contact that provides a definitive status output to control logic or interlocks, enabling motor controllers and starters to respond quickly to a misphased condition, while wiring is accomplished via screw terminals for straightforward installation. In Siemens' legacy lineup, 3UG4511-1AP20 covers a lower voltage range (320–500 V) and is documented as having 1 changeover contact, with 3UG5511-1AR20 listed as the recommended successor; the AQ20 version thus represents the higher-voltage variant in this family. Common applications include protecting motors, pumps, and conveyors by verifying correct phase sequence before energization, enabling safe start-up sequences in switchgear and control panels, and providing a simple, reliable interface for PLCs and automation systems that require phase-order confirmation.